Spring Cloud Config

Spring Cloud Config provides server and client-side support for externalized configuration in a distributed system. With the Config Server you have a central place to manage external properties for applications across all environments. The concepts on both client and server map identically to the Spring Environment and PropertySource abstractions, so they fit very well with Spring applications, but can be used with any application running in any language. As an application moves through the deployment pipeline from dev to test and into production you can manage the configuration between those environments and be certain that applications have everything they need to run when they migrate. The default implementation of the server storage backend uses git so it easily supports labelled versions of configuration environments, as well as being accessible to a wide range of tooling for managing the content. It is easy to add alternative implementations and plug them in with Spring configuration.

Features

Spring Cloud Config Server features:

HTTP, resource-based API for external configuration (name-value pairs, or equivalent YAML content)
Encrypt and decrypt property values (symmetric or asymmetric)
Embeddable easily in a Spring Boot application using @EnableConfigServer

Config Client features (for Spring applications):

Bind to the Config Server and initialize Spring Environment with remote property sources
Encrypt and decrypt property values (symmetric or asymmetric)
@RefreshScope for Spring @Beans that want to be re-initialized when configuration changes
Management endpoints:
- /env/ for updating Environment and rebinding @ConfigurationProperties
- /refresh for refreshing the @RefreshScope beans
- /restart for restarting the Spring context (disabled by default)
- /pause and /resume for calling the Lifecycle methods (stop() and start() on the ApplicationContext)
Bootstrap appplication context: a parent context for the main application that can be trained to do anything (by default it binds to the Config Server, and decrypts property values)

Quick Start

Start the server:

$ cd spring-cloud-config-server
$ mvn spring-boot:run

The server is a Spring Boot application so you can build the jar file and run that (java -jar …) or pull it down from a Maven repository. Then try it out as a client:

$ curl localhost:8888/foo/development
{"name":"development","label":"master","propertySources":[
  {"name":"https://github.com/scratches/config-repo/foo-development.properties","source":{"bar":"spam"}},
  {"name":"https://github.com/scratches/config-repo/foo.properties","source":{"foo":"bar"}}
]}

The default strategy for locating property sources is to clone a git repository (at "spring.platform.config.server.uri") and use it to initialize a mini SpringApplication. The mini-application’s Environment is used to enumerate property sources and publish them via a JSON endpoint. The service has resources in the form:

/{application}/{profile}[/{label}]

where the "application" is injected as the "spring.config.name" in the SpringApplication (i.e. what is normally "application" in a regular Spring Boot app), "profile" is an active profile (or comma-separated list of properties), and "label" is an optional git label (defaults to "master").

Client Side Usage

To use these features in an application, just build it as a Spring Boot application that depends on spring-cloud-config-client (e.g. see the test cases for the config-client, or the sample app). When it runs it will pick up the external configuration from the default local config server on port 8888 if it is running. To modify the startup behaviour you can change the location of the config server using bootstrap.properties (like application.properties but for the bootstrap phase of an application context), e.g.

spring.platform.config.uri: http://myconfigserver.com

The bootstrap properties will show up in the /env endpoint as a high-priority property source, e.g.

$ curl localhost:8080/env
{
  "profiles":[],
  "configService:https://github.com/scratches/config-repo/bar.properties":{"foo":"bar"},
  "servletContextInitParams":{},
  "systemProperties":{...},
  ...
}

(a property source called "configService:<URL of remote repository>/<file name>" contains the property "foo" with value "bar" and is highest priority).

Sample Application

There is a sample application here. It is a Spring Boot application so you can run it using the usual mechanisms (for instance "mvn spring-boot:run"). When it runs it will look for the config server on "http://localhost:8888" by default, so you could run the server as well to see it all working together.

The sample has a test case where the config server is also started in the same JVM (with a different port), and the test asserts that an environment property from the git configuration repo is present. To change the location of the config server just set "spring.platform.config.uri" in "bootstrap.yml" (or via System properties etc.).

The test case has a main() method that runs the server in the same way (watch the logs for its port), so you can run the whole system in one process and play with it (e.g. right click on the main in your IDE and run it). The main() method uses target/config for the working directory of the git repository, so you can make local changes there and see them reflected in the running app.

$ curl localhost:8080/env/foo
bar
$ vi target/config/bar.properties
.. change value of "foo", optionally commit
$ curl localhost:8080/refresh
["foo"]
$ curl localhost:8080/env/foo
baz

The refresh endpoint reports that the "foo" property changed.

Last updated 2014-09-26 11:35:20 BST

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README.md Unescape Escape

Spring Cloud Config

Features

Quick Start

Client Side Usage

Sample Application

README.md