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Add some documentation on DiscoveryClient

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and how to use it. In particular you can't use it before the
ApplicationContext is past phase=0 of lifecycle startup.

Fixes gh-48
This commit is contained in:
Dave Syer
2014-11-05 17:23:54 +00:00
parent d944145ce3
commit bebcf66041
1 changed files with 37 additions and 2 deletions
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39
docs/src/main/asciidoc/spring-cloud-netflix.adoc
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@@ -60,10 +60,43 @@ registry to locate other services). The instance behaviour is driven
by `eureka.instance.*` configuration keys, but the defaults will be
fine if you ensure that your application has a
`spring.application.name` (this is the default for the Eureka service
ID, or VIP).
ID, or VIP).
See {github-code}/spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/eureka/EurekaInstanceConfigBean.java[EurekaInstanceConfigBean] and {github-code}/spring-cloud-netflix-core/src/main/java/org/springframework/cloud/netflix/eureka/EurekaClientConfigBean.java[EurekaClientConfigBean] for more details of the configurable options.
=== Using the DiscoveryClient
Once you have an app that is `@EnableEurekaClient` you can use it to
discover service instances from the <<spring-cloud-eureka-server,
Eureka Server>>. One way to do that is to use the native `DiscoveryClient`, e.g.
----
@Autowired
private DiscoveryClient discoveryClient;
public String serviceUrl() {
InstanceInfo instance = discoveryClient.getNextServerFromEureka("STORES", false);
return instance.getHomePageUrl();
}
----
[TIP]
====
Don't use the `DiscoveryClient` in `@PostConstruct` method (or
anywhere where the `ApplicationContext` might not be started yet). It
is initialized in a `SmartLifecycle` (with `phase=0`) so the earliest
you can rely on it being available is in another `SmartLifecycle` with
higher phase.
=== Alternatives to the DiscoveryClient
You don't have to use the raw Netflix `DiscoveryClient` and usually it
is more convenient to use it behind a wrapper of some sort. Spring
Cloud has support for <<spring-cloud-feign, Feign>> (a REST client
builder) and also <<spring-cloud-ribbon, Spring `RestTemplate`>> using
the logical Eureka service identifiers (VIPs) instead of physical
URLs.
=== Why is it so Slow to Register a Service?
Being an instance also involves a periodic heartbeat to the registry
@@ -77,7 +110,7 @@ production it's probably better to stick with the default because
there are some computations internally in the server that make
assumptions about the lease renewal period.
[[spring-cloud-eureka-server]]
== Service Discovery: Eureka Server
Example eureka server:
@@ -319,6 +352,7 @@ turbine:
The clusterName can be customized by a SPEL expression in `turbine.clusterNameExpression`. For example, `turbine.clusterNameExpression=aSGName` would get the clustername from the AWS ASG name.
[[spring-cloud-feign]]
== Declarative REST Client: Feign
https://github.com/Netflix/feign[Feign] is a declarative web service client. It makes writing web service clients easier. To use Feign create an interface and annotate it. It has pluggable annotation support including Feign annotations and JAX-RS annotations. Feign also supports pluggable encoders and decoders. Spring Cloud adds support for Spring MVC annotations and for using the same `HttpMessageConverters` used by default in Spring Web. Spring Cloud integrates Ribbon and Eureka to provide a load balanced http client when using Feign.
@@ -357,6 +391,7 @@ public interface StoreClient {
}
----
[[spring-cloud-ribbon]]
== Client Side Load Balancer: Ribbon
Usage of `LoadBalancerClient` directly: