spring-cloud-static/spring-cloud-kubernetes/1.0.0.RC2/spring-cloud-kubernetes.xml

<?xml version="1.0" encoding="UTF-8"?>
<?asciidoc-toc?>
<?asciidoc-numbered?>
<book xmlns="http://docbook.org/ns/docbook" xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en">
<info>
<title>Spring Cloud Kubernetes</title>
<date>2018-12-21</date>
</info>
<chapter xml:id="_why_do_you_need_spring_cloud_kubernetes">
<title>Why do you need Spring Cloud Kubernetes?</title>
<simpara>Spring Cloud Kubernetes provide Spring Cloud common interfaces implementations to consume Kubernetes native services.
The main objective of the projects provided in this repository is to facilitate the integration of Spring Cloud/Spring Boot applications running inside Kubernetes.</simpara>
</chapter>
<chapter xml:id="_discoveryclient_for_kubernetes">
<title>DiscoveryClient for Kubernetes</title>
<simpara>This project provides an implementation of <link xl:href="https://github.com/spring-cloud/spring-cloud-commons/blob/master/spring-cloud-commons/src/main/java/org/springframework/cloud/client/discovery/DiscoveryClient.java">Discovery Client</link>
for <link xl:href="http://kubernetes.io">Kubernetes</link>.
This allows you to query Kubernetes endpoints <emphasis role="strong">(see <link xl:href="http://kubernetes.io/docs/user-guide/services/">services</link>)</emphasis> by name.
A service is typically exposed by the Kubernetes API server as a collection of endpoints which represent <literal>http</literal>, <literal>https</literal> addresses that a client can
access from a Spring Boot application running as a pod. This discovery feature is also used by the Spring Cloud Kubernetes Ribbon project
to fetch the list of the endpoints defined for an application to be load balanced.</simpara>
<simpara>This is something that you get for free just by adding the following dependency inside your project:</simpara>
<programlisting language="xml" linenumbering="unnumbered">&lt;dependency&gt;
    &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
    &lt;artifactId&gt;spring-cloud-starter-kubernetes&lt;/artifactId&gt;
    &lt;version&gt;${latest.version}&lt;/version&gt;
&lt;/dependency&gt;</programlisting>
<simpara>To enable loading of the <literal>DiscoveryClient</literal>, add <literal>@EnableDiscoveryClient</literal> to the according configuration or application class like this:</simpara>
<programlisting language="java" linenumbering="unnumbered">@SpringBootApplication
@EnableDiscoveryClient
public class Application {
  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }
}</programlisting>
<simpara>Then you can inject the client in your code simply by:</simpara>
<programlisting language="java" linenumbering="unnumbered">@Autowired
private DiscoveryClient discoveryClient;</programlisting>
<simpara>If for any reason you need to disable the <literal>DiscoveryClient</literal> you can simply set the following property in <literal>application.properties</literal>:</simpara>
<screen>spring.cloud.kubernetes.discovery.enabled=false</screen>
<simpara>Some Spring Cloud components use the <literal>DiscoveryClient</literal> in order to obtain info about the local service instance. For
this to work you need to align the Kubernetes service name with the <literal>spring.application.name</literal> property.</simpara>
</chapter>
<chapter xml:id="_kubernetes_native_service_discovery">
<title>Kubernetes native service discovery</title>
<simpara>Kubernetes itself is capable of (server side) service discovery (see: <link xl:href="https://kubernetes.io/docs/concepts/services-networking/service/#discovering-services">https://kubernetes.io/docs/concepts/services-networking/service/#discovering-services</link>).
Using native kubernetes service discovery ensures compatibility with additional tooling, like: istio <link xl:href="https://istio.io">https://istio.io</link> (service mesh, capable of load balancing, ribbon, circuit breaker, failover and much more).</simpara>
<simpara>The caller service just needs to refer to names resolvable in particular kubernetes cluster then. Simplest implementation might use the spring <literal>RestTemplate</literal> referring to fully qualified domain name (FQDN) <literal><link xl:href="http://{service-name}.{namespace}.svc.{cluster}.local:{service-port}">http://{service-name}.{namespace}.svc.{cluster}.local:{service-port}</link></literal>.</simpara>
<simpara>Additionally, hystrix can be used for:</simpara>
<itemizedlist>
<listitem>
<simpara>circuit breaker implementation on the caller side, just by annotating the spring boot application class: <literal>@EnableCircuitBreaker</literal></simpara>
</listitem>
<listitem>
<simpara>and for the fallback functionality, annotating the respective method via: <literal>@HystrixCommand(fallbackMethod=</literal> does the job.</simpara>
</listitem>
</itemizedlist>
</chapter>
<chapter xml:id="_kubernetes_propertysource_implementations">
<title>Kubernetes PropertySource implementations</title>
<simpara>The most common approach to configure your Spring Boot application is to create an <literal>application.properties|yaml</literal> or
an <literal>application-profile.properties|yaml</literal> file containing key-value pairs providing customization values to your
application or Spring Boot starters. Users may override these properties by specifying system properties or environment
variables.</simpara>
<section xml:id="_configmap_propertysource">
<title>ConfigMap PropertySource</title>
<simpara>Kubernetes provides a resource named <link xl:href="http://kubernetes.io/docs/user-guide/configmap/">ConfigMap</link> to externalize the
parameters to pass to your application in the form of key-value pairs or embedded <literal>application.properties|yaml</literal> files.
The <link xl:href="./spring-cloud-kubernetes-config">Spring Cloud Kubernetes Config</link> project makes Kubernetes `ConfigMap`s available
during application bootstrapping and triggers hot reloading of beans or Spring context when changes are detected on
observed `ConfigMap`s.</simpara>
<simpara>The default behavior is to create a <literal>ConfigMapPropertySource</literal> based on a Kubernetes <literal>ConfigMap</literal> which has <literal>metadata.name</literal> of either the name of
your Spring application (as defined by its <literal>spring.application.name</literal> property) or a custom name defined within the
<literal>bootstrap.properties</literal> file under the following key <literal>spring.cloud.kubernetes.config.name</literal>.</simpara>
<simpara>However, more advanced configuration are possible where multiple ConfigMaps can be used
This is made possible by the <literal>spring.cloud.kubernetes.config.sources</literal> list.
For example one could define the following ConfigMaps</simpara>
<programlisting language="yaml" linenumbering="unnumbered">spring:
  application:
    name: cloud-k8s-app
  cloud:
    kubernetes:
      config:
        name: default-name
        namespace: default-namespace
        sources:
         # Spring Cloud Kubernetes will lookup a ConfigMap named c1 in namespace default-namespace
         - name: c1
         # Spring Cloud Kubernetes will lookup a ConfigMap named default-name in whatever namespace n2
         - namespace: n2
         # Spring Cloud Kubernetes will lookup a ConfigMap named c3 in namespace n3
         - namespace: n3
           name: c3</programlisting>
<simpara>In the example above, it <literal>spring.cloud.kubernetes.config.namespace</literal> had not been set,
then the ConfigMap named <literal>c1</literal> would be looked up in the namespace that the application runs</simpara>
<simpara>Any matching <literal>ConfigMap</literal> that is found, will be processed as follows:</simpara>
<itemizedlist>
<listitem>
<simpara>apply individual configuration properties.</simpara>
</listitem>
<listitem>
<simpara>apply as <literal>yaml</literal> the content of any property named <literal>application.yaml</literal></simpara>
</listitem>
<listitem>
<simpara>apply as properties file the content of any property named <literal>application.properties</literal></simpara>
</listitem>
</itemizedlist>
<simpara>The single exception to the aforementioned flow is when the <literal>ConfigMap</literal> contains a <emphasis role="strong">single</emphasis> key that indicates
the file is a YAML or Properties file. In that case the name of the key does NOT have to be <literal>application.yaml</literal> or
<literal>application.properties</literal> (it can be anything) and the value of the property will be treated correctly.
This features facilitates the use case where the <literal>ConfigMap</literal> was created using something like:</simpara>
<simpara><literal>kubectl create configmap game-config --from-file=/path/to/app-config.yaml</literal></simpara>
<simpara>Example:</simpara>
<simpara>Let&#8217;s assume that we have a Spring Boot application named <literal>demo</literal> that uses properties to read its thread pool
configuration.</simpara>
<itemizedlist>
<listitem>
<simpara><literal>pool.size.core</literal></simpara>
</listitem>
<listitem>
<simpara><literal>pool.size.maximum</literal></simpara>
</listitem>
</itemizedlist>
<simpara>This can be externalized to config map in <literal>yaml</literal> format:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  pool.size.core: 1
  pool.size.max: 16</programlisting>
<simpara>Individual properties work fine for most cases but sometimes embedded <literal>yaml</literal> is more convenient. In this case we will
use a single property named <literal>application.yaml</literal> to embed our <literal>yaml</literal>:</simpara>
<literallayout class="monospaced"> ```yaml
kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yaml: |-
    pool:
      size:
        core: 1
        max:16</literallayout>
<screen>The following also works:

 ```yaml
kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  custom-name.yaml: |-
    pool:
      size:
        core: 1
        max:16</screen>
<simpara>Spring Boot applications can also be configured differently depending on active profiles which will be merged together
when the ConfigMap is read. It is possible to provide different property values for different profiles using an
<literal>application.properties|yaml</literal> property, specifying profile-specific values each in their own document
(indicated by the <literal>---</literal> sequence) as follows:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">kind: ConfigMap
apiVersion: v1
metadata:
  name: demo
data:
  application.yml: |-
    greeting:
      message: Say Hello to the World
    farewell:
      message: Say Goodbye
    ---
    spring:
      profiles: development
    greeting:
      message: Say Hello to the Developers
    farewell:
      message: Say Goodbye to the Developers
    ---
    spring:
      profiles: production
    greeting:
      message: Say Hello to the Ops</programlisting>
<simpara>In the above case, the configuration loaded into your Spring Application with the <literal>development</literal> profile will be:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">  greeting:
    message: Say Hello to the Developers
  farewell:
    message: Say Goodbye to the Developers</programlisting>
<simpara>whereas if the <literal>production</literal> profile is active, the configuration will be:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">  greeting:
    message: Say Hello to the Ops
  farewell:
    message: Say Goodbye</programlisting>
<simpara>If both profiles are active, the property which appears last within the configmap will overwrite preceding values.</simpara>
<simpara>To tell to Spring Boot which <literal>profile</literal> should be enabled at bootstrap, a system property can be passed to the Java
command launching your Spring Boot application using an env variable that you will define with the OpenShift
<literal>DeploymentConfig</literal> or Kubernetes <literal>ReplicationConfig</literal> resource file as follows:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">apiVersion: v1
kind: DeploymentConfig
spec:
  replicas: 1
  ...
    spec:
      containers:
      - env:
        - name: JAVA_APP_DIR
          value: /deployments
        - name: JAVA_OPTIONS
          value: -Dspring.profiles.active=developer</programlisting>
<simpara><emphasis role="strong">Notes:</emphasis>
- check the security configuration section, to access config maps from inside a pod you need to have the correct
Kubernetes service accounts, roles and role bindings.</simpara>
<simpara>Another option for using ConfigMaps, is to mount them into the Pod running the Spring Cloud Kubernetes application
and have Spring Cloud Kubernetes read them from the file system.
This behavior is controlled by the <literal>spring.cloud.kubernetes.config.paths</literal> property and can be used in
addition to or instead of the mechanism described earlier.
Multiple (exact) file paths can be specified in <literal>spring.cloud.kubernetes.config.paths</literal> by using the <literal>,</literal> delimiter</simpara>
<table frame="all" rowsep="1" colsep="1">
<title>Properties:</title>
<tgroup cols="4">
<colspec colname="col_1" colwidth="25*"/>
<colspec colname="col_2" colwidth="25*"/>
<colspec colname="col_3" colwidth="25*"/>
<colspec colname="col_4" colwidth="25*"/>
<thead>
<row>
<entry align="left" valign="top">Name</entry>
<entry align="left" valign="top">Type</entry>
<entry align="left" valign="top">Default</entry>
<entry align="left" valign="top">Description</entry>
</row>
</thead>
<tbody>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.config.enabled</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>true</simpara></entry>
<entry align="left" valign="top"><simpara>Enable Secrets PropertySource</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.config.name</simpara></entry>
<entry align="left" valign="top"><simpara>String</simpara></entry>
<entry align="left" valign="top"><simpara>${spring.application.name}</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the name of ConfigMap to lookup</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.config.namespace</simpara></entry>
<entry align="left" valign="top"><simpara>String</simpara></entry>
<entry align="left" valign="top"><simpara>Client namespace</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the Kubernetes namespace where to lookup</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.config.paths</simpara></entry>
<entry align="left" valign="top"><simpara>List</simpara></entry>
<entry align="left" valign="top"><simpara>null</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the paths where ConfigMaps are mounted</simpara></entry>
</row>
</tbody>
<tfoot>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.config.enableApi</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>true</simpara></entry>
<entry align="left" valign="top"><simpara>Enable/Disable consuming ConfigMaps via APIs</simpara></entry>
</row>
</tfoot>
</tgroup>
</table>
</section>
<section xml:id="_secrets_propertysource">
<title>Secrets PropertySource</title>
<simpara>Kubernetes has the notion of [Secrets](<link xl:href="https://kubernetes.io/docs/concepts/configuration/secret/">https://kubernetes.io/docs/concepts/configuration/secret/</link>) for storing
sensitive data such as password, OAuth tokens, etc. This project provides integration with <literal>Secrets</literal> to make secrets
accessible by Spring Boot applications. This feature can be explicitly enabled/disabled using the <literal>spring.cloud.kubernetes.secrets.enabled</literal> property.</simpara>
<simpara>The <literal>SecretsPropertySource</literal> when enabled will lookup Kubernetes for <literal>Secrets</literal> from the following sources:
1. reading recursively from secrets mounts
2. named after the application (as defined by <literal>spring.application.name</literal>)
3. matching some labels</simpara>
<simpara>Please note that by default, consuming Secrets via API (points 2 and 3 above) <emphasis role="strong">is not enabled</emphasis> for security reasons
 and it is recommend that containers share secrets via mounted volumes. Otherwise proper RBAC security configurations must be provided
 to make sure that unauthorized access to Secrets occurs.</simpara>
<simpara>If the secrets are found their data is made available to the application.</simpara>
<simpara><emphasis role="strong">Example:</emphasis></simpara>
<simpara>Let&#8217;s assume that we have a spring boot application named <literal>demo</literal> that uses properties to read its database
configuration. We can create a Kubernetes secret using the following command:</simpara>
<screen>oc create secret generic db-secret --from-literal=username=user --from-literal=password=p455w0rd</screen>
<simpara>This would create the following secret (shown using <literal>oc get secrets db-secret -o yaml</literal>):</simpara>
<programlisting language="yaml" linenumbering="unnumbered">apiVersion: v1
data:
  password: cDQ1NXcwcmQ=
  username: dXNlcg==
kind: Secret
metadata:
  creationTimestamp: 2017-07-04T09:15:57Z
  name: db-secret
  namespace: default
  resourceVersion: "357496"
  selfLink: /api/v1/namespaces/default/secrets/db-secret
  uid: 63c89263-6099-11e7-b3da-76d6186905a8
type: Opaque</programlisting>
<simpara>Note that the data contains Base64-encoded versions of the literal provided by the create command.</simpara>
<simpara>This secret can then be used by your application for example by exporting the secret&#8217;s value as environment variables:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">apiVersion: v1
kind: Deployment
metadata:
  name: ${project.artifactId}
spec:
   template:
     spec:
       containers:
         - env:
            - name: DB_USERNAME
              valueFrom:
                 secretKeyRef:
                   name: db-secret
                   key: username
            - name: DB_PASSWORD
              valueFrom:
                 secretKeyRef:
                   name: db-secret
                   key: password</programlisting>
<simpara>You can select the Secrets to consume in a number of ways:</simpara>
<orderedlist numeration="arabic">
<listitem>
<simpara>By listing the directories where secrets are mapped:
<literal>`
-Dspring.cloud.kubernetes.secrets.paths=/etc/secrets/db-secret,etc/secrets/postgresql
</literal>`</simpara>
<literallayout class="monospaced">If you have all the secrets mapped to a common root, you can set them like:</literallayout>
<literallayout class="monospaced">```
-Dspring.cloud.kubernetes.secrets.paths=/etc/secrets
```</literallayout>
</listitem>
<listitem>
<simpara>By setting a named secret:
<literal>`
-Dspring.cloud.kubernetes.secrets.name=db-secret
</literal>`</simpara>
</listitem>
<listitem>
<simpara>By defining a list of labels:
<literal>`
-Dspring.cloud.kubernetes.secrets.labels.broker=activemq
-Dspring.cloud.kubernetes.secrets.labels.db=postgresql
</literal>`</simpara>
</listitem>
</orderedlist>
<table frame="all" rowsep="1" colsep="1">
<title>Properties:</title>
<tgroup cols="4">
<colspec colname="col_1" colwidth="25*"/>
<colspec colname="col_2" colwidth="25*"/>
<colspec colname="col_3" colwidth="25*"/>
<colspec colname="col_4" colwidth="25*"/>
<thead>
<row>
<entry align="left" valign="top">Name</entry>
<entry align="left" valign="top">Type</entry>
<entry align="left" valign="top">Default</entry>
<entry align="left" valign="top">Description</entry>
</row>
</thead>
<tbody>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.secrets.enabled</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>true</simpara></entry>
<entry align="left" valign="top"><simpara>Enable Secrets PropertySource</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.secrets.name</simpara></entry>
<entry align="left" valign="top"><simpara>String</simpara></entry>
<entry align="left" valign="top"><simpara>${spring.application.name}</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the name of the secret to lookup</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.secrets.namespace</simpara></entry>
<entry align="left" valign="top"><simpara>String</simpara></entry>
<entry align="left" valign="top"><simpara>Client namespace</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the Kubernetes namespace where to lookup</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.secrets.labels</simpara></entry>
<entry align="left" valign="top"><simpara>Map</simpara></entry>
<entry align="left" valign="top"><simpara>null</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the labels used to lookup secrets</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.secrets.paths</simpara></entry>
<entry align="left" valign="top"><simpara>List</simpara></entry>
<entry align="left" valign="top"><simpara>null</simpara></entry>
<entry align="left" valign="top"><simpara>Sets the paths where secrets are mounted (example 1)</simpara></entry>
</row>
</tbody>
<tfoot>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.secrets.enableApi</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>false</simpara></entry>
<entry align="left" valign="top"><simpara>Enable/Disable consuming secrets via APIs (examples 2 and 3)</simpara></entry>
</row>
</tfoot>
</tgroup>
</table>
<simpara><emphasis role="strong">Notes:</emphasis>
- The property <literal>spring.cloud.kubernetes.secrets.labels</literal> behaves as defined by
<link xl:href="https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-Configuration-Binding#map-based-binding">Map-based binding</link>.
- The property <literal>spring.cloud.kubernetes.secrets.paths</literal> behaves as defined by
<link xl:href="https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-Configuration-Binding#collection-based-binding">Collection-based binding</link>.
- Access to secrets via API may be restricted for security reasons, the preferred way is to mount secret to the POD.</simpara>
<simpara>Example of application using secrets (though it hasn&#8217;t been updated to use the new <literal>spring-cloud-kubernetes</literal> project):
<link xl:href="https://github.com/fabric8-quickstarts/spring-boot-camel-config">spring-boot-camel-config</link></simpara>
</section>
<section xml:id="_propertysource_reload">
<title>PropertySource Reload</title>
<simpara>Some applications may need to detect changes on external property sources and update their internal status to reflect the new configuration.
The reload feature of Spring Cloud Kubernetes is able to trigger an application reload when a related <literal>ConfigMap</literal> or
<literal>Secret</literal> changes.</simpara>
<simpara>This feature is disabled by default and can be enabled using the configuration property <literal>spring.cloud.kubernetes.reload.enabled=true</literal>
 (eg. in the <emphasis role="strong">application.properties</emphasis> file).</simpara>
<simpara>The following levels of reload are supported (property <literal>spring.cloud.kubernetes.reload.strategy</literal>):
- <emphasis role="strong"><literal>refresh</literal> (default)</emphasis>: only configuration beans annotated with <literal>@ConfigurationProperties</literal> or <literal>@RefreshScope</literal> are reloaded.
This reload level leverages the refresh feature of Spring Cloud Context.
- <emphasis role="strong"><literal>restart_context</literal></emphasis>: the whole Spring <emphasis>ApplicationContext</emphasis> is gracefully restarted. Beans are recreated with the new configuration.
- <emphasis role="strong"><literal>shutdown</literal></emphasis>: the Spring <emphasis>ApplicationContext</emphasis> is shut down to activate a restart of the container.
 When using this level, make sure that the lifecycle of all non-daemon threads is bound to the ApplicationContext
 and that a replication controller or replica set is configured to restart the pod.</simpara>
<simpara>Example:</simpara>
<simpara>Assuming that the reload feature is enabled with default settings (<emphasis role="strong"><literal>refresh</literal></emphasis> mode), the following bean will be refreshed when the config map changes:</simpara>
<programlisting language="java" linenumbering="unnumbered">@Configuration
@ConfigurationProperties(prefix = "bean")
public class MyConfig {

    private String message = "a message that can be changed live";

    // getter and setters

}</programlisting>
<simpara>A way to see that changes effectively happen is creating another bean that prints the message periodically.</simpara>
<programlisting language="java" linenumbering="unnumbered">@Component
public class MyBean {

    @Autowired
    private MyConfig config;

    @Scheduled(fixedDelay = 5000)
    public void hello() {
        System.out.println("The message is: " + config.getMessage());
    }
}</programlisting>
<simpara>The message printed by the application can be changed using a <literal>ConfigMap</literal> as follows:</simpara>
<programlisting language="yaml" linenumbering="unnumbered">apiVersion: v1
kind: ConfigMap
metadata:
  name: reload-example
data:
  application.properties: |-
    bean.message=Hello World!</programlisting>
<simpara>Any change to the property named <literal>bean.message</literal> in the <literal>ConfigMap</literal> associated to the pod will be reflected in the
output. More generally speaking, changes associated to properties prefixed with the value defined by the <literal>prefix</literal>
field of the <literal>@ConfigurationProperties</literal> annotation will be detected and reflected in the application.
[Associating a <literal>ConfigMap</literal> to a pod](#configmap-propertysource) is explained above.</simpara>
<simpara>The full example is available in [spring-cloud-kubernetes-reload-example](spring-cloud-kubernetes-examples/kubernetes-reload-example).</simpara>
<simpara>The reload feature supports two operating modes:
- <emphasis role="strong">event (default)</emphasis>: watches for changes in config maps or secrets using the Kubernetes API (web socket).
Any event will produce a re-check on the configuration and a reload in case of changes.
The <literal>view</literal> role on the service account is required in order to listen for config map changes. A higher level role (eg. <literal>edit</literal>) is required for secrets
(secrets are not monitored by default).
- <emphasis role="strong">polling</emphasis>: re-creates the configuration periodically from config maps and secrets to see if it has changed.
The polling period can be configured using the property <literal>spring.cloud.kubernetes.reload.period</literal> and defaults to <emphasis role="strong">15 seconds</emphasis>.
It requires the same role as the monitored property source.
This means, for example, that using polling on file mounted secret sources does not require particular privileges.</simpara>
<table frame="all" rowsep="1" colsep="1">
<title>Properties:</title>
<tgroup cols="4">
<colspec colname="col_1" colwidth="25*"/>
<colspec colname="col_2" colwidth="25*"/>
<colspec colname="col_3" colwidth="25*"/>
<colspec colname="col_4" colwidth="25*"/>
<thead>
<row>
<entry align="left" valign="top">Name</entry>
<entry align="left" valign="top">Type</entry>
<entry align="left" valign="top">Default</entry>
<entry align="left" valign="top">Description</entry>
</row>
</thead>
<tbody>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.reload.enabled</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>false</simpara></entry>
<entry align="left" valign="top"><simpara>Enables monitoring of property sources and configuration reload</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.reload.monitoring-config-maps</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>true</simpara></entry>
<entry align="left" valign="top"><simpara>Allow monitoring changes in config maps</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.reload.monitoring-secrets</simpara></entry>
<entry align="left" valign="top"><simpara>Boolean</simpara></entry>
<entry align="left" valign="top"><simpara>false</simpara></entry>
<entry align="left" valign="top"><simpara>Allow monitoring changes in secrets</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.reload.strategy</simpara></entry>
<entry align="left" valign="top"><simpara>Enum</simpara></entry>
<entry align="left" valign="top"><simpara>refresh</simpara></entry>
<entry align="left" valign="top"><simpara>The strategy to use when firing a reload (<emphasis role="strong">refresh</emphasis>, <emphasis role="strong">restart_context</emphasis>, <emphasis role="strong">shutdown</emphasis>)</simpara></entry>
</row>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.reload.mode</simpara></entry>
<entry align="left" valign="top"><simpara>Enum</simpara></entry>
<entry align="left" valign="top"><simpara>event</simpara></entry>
<entry align="left" valign="top"><simpara>Specifies how to listen for changes in property sources (<emphasis role="strong">event</emphasis>, <emphasis role="strong">polling</emphasis>)</simpara></entry>
</row>
</tbody>
<tfoot>
<row>
<entry align="left" valign="top"><simpara>spring.cloud.kubernetes.reload.period</simpara></entry>
<entry align="left" valign="top"><simpara>Duration</simpara></entry>
<entry align="left" valign="top"><simpara>15s</simpara></entry>
<entry align="left" valign="top"><simpara>The period for verifying changes when using the <emphasis role="strong">polling</emphasis> strategy</simpara></entry>
</row>
</tfoot>
</tgroup>
</table>
<simpara><emphasis role="strong">Notes</emphasis>:
- Properties under <emphasis role="strong">spring.cloud.kubernetes.reload.</emphasis> should not be used in config maps or secrets: changing such properties at runtime may lead to unexpected results;
- Deleting a property or the whole config map does not restore the original state of the beans when using the <emphasis role="strong">refresh</emphasis> level.</simpara>
</section>
</chapter>
<chapter xml:id="_ribbon_discovery_in_kubernetes">
<title>Ribbon discovery in Kubernetes</title>
<simpara>Spring Cloud client applications calling a microservice should be interested on relying on a client load-balancing
feature in order to automatically discover at which endpoint(s) it can reach a given service. This mechanism has been
implemented within the [spring-cloud-kubernetes-ribbon](spring-cloud-kubernetes-ribbon/pom.xml) project where a
Kubernetes client will populate a <link xl:href="https://github.com/Netflix/ribbon">Ribbon</link> <literal>ServerList</literal> containing information
about such endpoints.</simpara>
<simpara>The implementation is part of the following starter that you can use by adding its dependency to your pom file:</simpara>
<programlisting language="xml" linenumbering="unnumbered">&lt;dependency&gt;
    &lt;groupId&gt;org.springframework.cloud&lt;/groupId&gt;
    &lt;artifactId&gt;spring-cloud-starter-kubernetes-ribbon&lt;/artifactId&gt;
    &lt;version&gt;${latest.version}&lt;/version&gt;
&lt;/dependency&gt;</programlisting>
<simpara>When the list of the endpoints is populated, the Kubernetes client will search the registered endpoints living in
the current namespace/project matching the service name defined using the Ribbon Client annotation:</simpara>
<programlisting language="java" linenumbering="unnumbered">@RibbonClient(name = "name-service")</programlisting>
<simpara>You can configure Ribbon&#8217;s behavior by providing properties in your <literal>application.properties</literal> (via your application&#8217;s
dedicated <literal>ConfigMap</literal>) using the following format: <literal>&lt;name of your service&gt;.ribbon.&lt;Ribbon configuration key&gt;</literal> where:</simpara>
<itemizedlist>
<listitem>
<simpara><literal>&lt;name of your service&gt;</literal> corresponds to the service name you&#8217;re accessing over Ribbon, as configured using the
<literal>@RibbonClient</literal> annotation (e.g. <literal>name-service</literal> in the example above)</simpara>
</listitem>
<listitem>
<simpara><literal>&lt;Ribbon configuration key&gt;</literal> is one of the Ribbon configuration key defined by
<link xl:href="https://github.com/Netflix/ribbon/blob/master/ribbon-core/src/main/java/com/netflix/client/config/CommonClientConfigKey.java">Ribbon&#8217;s CommonClientConfigKey class</link></simpara>
</listitem>
</itemizedlist>
<simpara>Additionally, the <literal>spring-cloud-kubernetes-ribbon</literal> project defines two additional configuration keys to further
control how Ribbon interacts with Kubernetes. In particular, if an endpoint defines multiple ports, the default
behavior is to use the first one found. To select more specifically which port to use, in a multi-port service, use
the <literal>PortName</literal> key. If you want to specify in which Kubernetes' namespace the target service should be looked up, use
the <literal>KubernetesNamespace</literal> key, remembering in both instances to prefix these keys with your service name and
<literal>ribbon</literal> prefix as specified above.</simpara>
<simpara>Examples that are using this module for ribbon discovery are:</simpara>
<itemizedlist>
<listitem>
<simpara><link xl:href="./spring-cloud-kubernetes-examples/kubernetes-circuitbreaker-ribbon-example">Spring Cloud Circuitbreaker and Ribbon</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://github.com/fabric8-quickstarts/spring-boot-ribbon">fabric8-quickstarts - Spring Boot - Ribbon</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://github.com/fabric8io/kubeflix/tree/master/examples/loanbroker/bank">Kubeflix - LoanBroker - Bank</link></simpara>
</listitem>
</itemizedlist>
<simpara><emphasis role="strong">Note</emphasis>: The Ribbon discovery client can be disabled by setting this key within the application properties file
<literal>spring.cloud.kubernetes.ribbon.enabled=false</literal>.</simpara>
</chapter>
<chapter xml:id="_kubernetes_ecosystem_awareness">
<title>Kubernetes Ecosystem Awareness</title>
<simpara>All of the features described above will work equally well regardless of whether your application is running inside
Kubernetes or not. This is really helpful for development and troubleshooting.
From a development point of view, this is really helpful as you can start your Spring Boot application and debug one
of the modules part of this project. It is not required to deploy it in Kubernetes
as the code of the project relies on the
<link xl:href="https://github.com/fabric8io/kubernetes-client">Fabric8 Kubernetes Java client</link> which is a fluent DSL able to
communicate using <literal>http</literal> protocol to the REST API of Kubernetes Server.</simpara>
<section xml:id="_kubernetes_profile_autoconfiguration">
<title>Kubernetes Profile Autoconfiguration</title>
<simpara>When the application runs as a pod inside Kubernetes a Spring profile named <literal>kubernetes</literal> will automatically get activated.
This allows the developer to customize the configuration, to define beans that will be applied when the Spring Boot application is deployed
within the Kubernetes platform <emphasis role="strong">(e.g. different dev and prod configuration)</emphasis>.</simpara>
</section>
<section xml:id="_istio_awareness">
<title>Istio Awareness</title>
<simpara>When including the <emphasis role="strong">spring-cloud-kubernetes-istio</emphasis> module into the application classpath a new profile will be added to the application,
if the application is running inside a Kubernetes Cluster with <link xl:href="http://istio.io">Istio</link> installed. Then you can use
spring <emphasis role="strong">@Profile("istio")</emphasis> annotations into your Beans and <emphasis role="strong">@Configuration</emphasis>'s.</simpara>
<simpara>The Istio awareness module uses the <emphasis role="strong">me.snowdrop:istio-client</emphasis> to interact with Istio APIs enabling us to discover traffic rules, circuit breakers, etc.
Making it easy for our Spring Boot applications to consume this data to dynamically configure themselves according the environment.</simpara>
</section>
</chapter>
<chapter xml:id="_pod_health_indicator">
<title>Pod Health Indicator</title>
<simpara>Spring Boot uses <link xl:href="https://github.com/spring-projects/spring-boot/blob/master/spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/HealthEndpoint.java">HealthIndicator</link> to expose info about the health of an application.
That makes it really useful for exposing health related information to the user and are also a good fit for use as <link xl:href="https://kubernetes.io/docs/tasks/configure-pod-container/configure-liveness-readiness-probes/">readiness probes</link>.</simpara>
<simpara>The Kubernetes health indicator which is part of the core module exposes the following info:</simpara>
<itemizedlist>
<listitem>
<simpara>pod name, ip address, namespace, service account, node name and its ip address</simpara>
</listitem>
<listitem>
<simpara>flag that indicates if the Spring Boot application is internal or external to Kubernetes</simpara>
</listitem>
</itemizedlist>
</chapter>
<chapter xml:id="_leader_election">
<title>Leader Election</title>
<simpara>&lt;TBD&gt;</simpara>
</chapter>
<chapter xml:id="_security_configurations_inside_kubernetes">
<title>Security Configurations inside Kubernetes</title>
<section xml:id="_namespace">
<title>Namespace</title>
<simpara>Most of the components provided in this project need to know the namespace. For Kubernetes (1.3+) the namespace is made available to pod as part of the service account secret and automatically detected by the client.
For earlier version it needs to be specified as an env var to the pod. A quick way to do this is:</simpara>
<literallayout class="monospaced">env:
- name: "KUBERNETES_NAMESPACE"
  valueFrom:
    fieldRef:
      fieldPath: "metadata.namespace"</literallayout>
</section>
<section xml:id="_service_account">
<title>Service Account</title>
<simpara>For distros of Kubernetes that support more fine-grained role-based access within the cluster, you need to make sure a pod that runs with spring-cloud-kubernetes has access to the Kubernetes API.
For any service accounts you assign to a deployment/pod, you need to make sure it has the correct roles. For example, you can add <literal>cluster-reader</literal> permissions to your <literal>default</literal> service account depending on the project you&#8217;re in:</simpara>
</section>
</chapter>
<chapter xml:id="_examples">
<title>Examples</title>
<simpara>Spring Cloud Kubernetes tries to make it transparent for your applications to consume Kubernetes Native Services
following the Spring Cloud interfaces.</simpara>
<simpara>In your applications, you need to add the <emphasis role="strong">spring-cloud-kubernetes-discovery</emphasis> dependency to your classpath and remove any other dependency that contains a <emphasis role="strong">DiscoveryClient</emphasis> implementation (ie. Eureka Discovery Client).
The same applies for PropertySourceLocator, where you need to add to the classpath the <emphasis role="strong">spring-cloud-kubernetes-config</emphasis> and remove any other dependency that contains a <emphasis role="strong">PropertySourceLocator</emphasis> implementation (ie. Config Server Client).</simpara>
<simpara>The following projects highlight the usage of these dependencies and demonstrate how these libraries can be used from any Spring Boot application.</simpara>
<simpara>List of examples using these projects:</simpara>
<itemizedlist>
<listitem>
<simpara><link xl:href="https://github.com/spring-cloud/spring-cloud-kubernetes/tree/master/spring-cloud-kubernetes-examples">Spring Cloud Kubernetes Examples</link>: the ones located inside this repository.</simpara>
</listitem>
<listitem>
<simpara>Spring Cloud Kubernetes Full Example: Minions and Boss</simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://github.com/salaboy/spring-cloud-k8s-minion">Minion</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://github.com/salaboy/spring-cloud-k8s-boss">Boss</link></simpara>
</listitem>
<listitem>
<simpara>Spring Cloud Kubernetes Full Example: <link xl:href="https://github.com/salaboy/s1p_docs">SpringOne Platform Tickets Service</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://github.com/salaboy/s1p_gateway">Spring Cloud Gateway with Spring Cloud Kubernetes Discovery and Config</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://github.com/salaboy/showcase-admin-tool">Spring Boot Admin with Spring Cloud Kubernetes Discovery and Config</link></simpara>
</listitem>
</itemizedlist>
</chapter>
<chapter xml:id="_other_resources">
<title>Other Resources</title>
<simpara>Here you can find other resources such as presentations(slides) and videos about Spring Cloud Kubernetes.</simpara>
<itemizedlist>
<listitem>
<simpara><link xl:href="https://salaboy.com/2018/09/27/the-s1p-experience/">S1P Spring Cloud on PKS</link></simpara>
</listitem>
<listitem>
<simpara><link xl:href="https://salaboy.com/2018/07/18/ljc-july-18-spring-cloud-docker-k8s/">Spring Cloud, Docker, Kubernetes &#8594; London Java Community July 2018</link></simpara>
</listitem>
</itemizedlist>
<simpara>Please feel free to submit other resources via PR to <link xl:href="http://github.com/spring-cloud/spring-cloud-kubernetes">this repository</link>.</simpara>
</chapter>
<chapter xml:id="_building">
<title>Building</title>
<section xml:id="_basic_compile_and_test">
<title>Basic Compile and Test</title>
<simpara>To build the source you will need to install JDK 1.7.</simpara>
<simpara>Spring Cloud uses Maven for most build-related activities, and you
should be able to get off the ground quite quickly by cloning the
project you are interested in and typing</simpara>
<screen>$ ./mvnw install</screen>
<note>
<simpara>You can also install Maven (&gt;=3.3.3) yourself and run the <literal>mvn</literal> command
in place of <literal>./mvnw</literal> in the examples below. If you do that you also
might need to add <literal>-P spring</literal> if your local Maven settings do not
contain repository declarations for spring pre-release artifacts.</simpara>
</note>
<note>
<simpara>Be aware that you might need to increase the amount of memory
available to Maven by setting a <literal>MAVEN_OPTS</literal> environment variable with
a value like <literal>-Xmx512m -XX:MaxPermSize=128m</literal>. We try to cover this in
the <literal>.mvn</literal> configuration, so if you find you have to do it to make a
build succeed, please raise a ticket to get the settings added to
source control.</simpara>
</note>
<simpara>For hints on how to build the project look in <literal>.travis.yml</literal> if there
is one. There should be a "script" and maybe "install" command. Also
look at the "services" section to see if any services need to be
running locally (e.g. mongo or rabbit).  Ignore the git-related bits
that you might find in "before_install" since they&#8217;re related to setting git
credentials and you already have those.</simpara>
<simpara>The projects that require middleware generally include a
<literal>docker-compose.yml</literal>, so consider using
<link xl:href="http://compose.docker.io/">Docker Compose</link> to run the middeware servers
in Docker containers. See the README in the
<link xl:href="https://github.com/spring-cloud-samples/scripts">scripts demo
repository</link> for specific instructions about the common cases of mongo,
rabbit and redis.</simpara>
<note>
<simpara>If all else fails, build with the command from <literal>.travis.yml</literal> (usually
<literal>./mvnw install</literal>).</simpara>
</note>
</section>
<section xml:id="_documentation">
<title>Documentation</title>
<simpara>The spring-cloud-build module has a "docs" profile, and if you switch
that on it will try to build asciidoc sources from
<literal>src/main/asciidoc</literal>. As part of that process it will look for a
<literal>README.adoc</literal> and process it by loading all the includes, but not
parsing or rendering it, just copying it to <literal>${main.basedir}</literal>
(defaults to <literal>${basedir}</literal>, i.e. the root of the project). If there are
any changes in the README it will then show up after a Maven build as
a modified file in the correct place. Just commit it and push the change.</simpara>
</section>
<section xml:id="_working_with_the_code">
<title>Working with the code</title>
<simpara>If you don&#8217;t have an IDE preference we would recommend that you use
<link xl:href="http://www.springsource.com/developer/sts">Spring Tools Suite</link> or
<link xl:href="http://eclipse.org">Eclipse</link> when working with the code. We use the
<link xl:href="http://eclipse.org/m2e/">m2eclipse</link> eclipse plugin for maven support. Other IDEs and tools
should also work without issue as long as they use Maven 3.3.3 or better.</simpara>
<section xml:id="_importing_into_eclipse_with_m2eclipse">
<title>Importing into eclipse with m2eclipse</title>
<simpara>We recommend the <link xl:href="http://eclipse.org/m2e/">m2eclipse</link> eclipse plugin when working with
eclipse. If you don&#8217;t already have m2eclipse installed it is available from the "eclipse
marketplace".</simpara>
<note>
<simpara>Older versions of m2e do not support Maven 3.3, so once the
projects are imported into Eclipse you will also need to tell
m2eclipse to use the right profile for the projects.  If you
see many different errors related to the POMs in the projects, check
that you have an up to date installation.  If you can&#8217;t upgrade m2e,
add the "spring" profile to your <literal>settings.xml</literal>. Alternatively you can
copy the repository settings from the "spring" profile of the parent
pom into your <literal>settings.xml</literal>.</simpara>
</note>
</section>
<section xml:id="_importing_into_eclipse_without_m2eclipse">
<title>Importing into eclipse without m2eclipse</title>
<simpara>If you prefer not to use m2eclipse you can generate eclipse project metadata using the
following command:</simpara>
<screen>$ ./mvnw eclipse:eclipse</screen>
<simpara>The generated eclipse projects can be imported by selecting <literal>import existing projects</literal>
from the <literal>file</literal> menu.</simpara>
</section>
</section>
</chapter>
<chapter xml:id="_contributing">
<title>Contributing</title>
<simpara>Spring Cloud is released under the non-restrictive Apache 2.0 license,
and follows a very standard Github development process, using Github
tracker for issues and merging pull requests into master. If you want
to contribute even something trivial please do not hesitate, but
follow the guidelines below.</simpara>
<section xml:id="_sign_the_contributor_license_agreement">
<title>Sign the Contributor License Agreement</title>
<simpara>Before we accept a non-trivial patch or pull request we will need you to sign the
<link xl:href="https://cla.pivotal.io/sign/spring">Contributor License Agreement</link>.
Signing the contributor&#8217;s agreement does not grant anyone commit rights to the main
repository, but it does mean that we can accept your contributions, and you will get an
author credit if we do.  Active contributors might be asked to join the core team, and
given the ability to merge pull requests.</simpara>
</section>
<section xml:id="_code_of_conduct">
<title>Code of Conduct</title>
<simpara>This project adheres to the Contributor Covenant <link xl:href="https://github.com/spring-cloud/spring-cloud-build/blob/master/docs/src/main/asciidoc/code-of-conduct.adoc">code of
conduct</link>. By participating, you  are expected to uphold this code. Please report
unacceptable behavior to <link xl:href="mailto:spring-code-of-conduct@pivotal.io">spring-code-of-conduct@pivotal.io</link>.</simpara>
</section>
<section xml:id="_code_conventions_and_housekeeping">
<title>Code Conventions and Housekeeping</title>
<simpara>None of these is essential for a pull request, but they will all help.  They can also be
added after the original pull request but before a merge.</simpara>
<itemizedlist>
<listitem>
<simpara>Use the Spring Framework code format conventions. If you use Eclipse
you can import formatter settings using the
<literal>eclipse-code-formatter.xml</literal> file from the
<link xl:href="https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-dependencies-parent/eclipse-code-formatter.xml">Spring
Cloud Build</link> project. If using IntelliJ, you can use the
<link xl:href="http://plugins.jetbrains.com/plugin/6546">Eclipse Code Formatter
Plugin</link> to import the same file.</simpara>
</listitem>
<listitem>
<simpara>Make sure all new <literal>.java</literal> files to have a simple Javadoc class comment with at least an
<literal>@author</literal> tag identifying you, and preferably at least a paragraph on what the class is
for.</simpara>
</listitem>
<listitem>
<simpara>Add the ASF license header comment to all new <literal>.java</literal> files (copy from existing files
in the project)</simpara>
</listitem>
<listitem>
<simpara>Add yourself as an <literal>@author</literal> to the .java files that you modify substantially (more
than cosmetic changes).</simpara>
</listitem>
<listitem>
<simpara>Add some Javadocs and, if you change the namespace, some XSD doc elements.</simpara>
</listitem>
<listitem>
<simpara>A few unit tests would help a lot as well&#8201;&#8212;&#8201;someone has to do it.</simpara>
</listitem>
<listitem>
<simpara>If no-one else is using your branch, please rebase it against the current master (or
other target branch in the main project).</simpara>
</listitem>
<listitem>
<simpara>When writing a commit message please follow <link xl:href="http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html">these conventions</link>,
if you are fixing an existing issue please add <literal>Fixes gh-XXXX</literal> at the end of the commit
message (where XXXX is the issue number).</simpara>
</listitem>
</itemizedlist>
</section>
</chapter>
</book>