7. Distributed Configuration with Zookeeper
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7. Distributed Configuration with Zookeeper

Zookeeper provides a hierarchical namespace that allows clients to store arbitrary data, such as configuration data. Spring Cloud Zookeeper Config is an alternative to the Config Server and Client. Configuration is loaded into the Spring Environment during the special "bootstrap" phase. Configuration is stored in the /config namespace by default. Multiple PropertySource instances are created based on the application’s name and the active profiles that mimicks the Spring Cloud Config order of resolving properties. For example, an application with the name "testApp" and with the "dev" profile will have the following property sources created:

config/testApp,dev
config/testApp
config/application,dev
config/application

The most specific property source is at the top, with the least specific at the bottom. Properties is the config/application namespace are applicable to all applications using zookeeper for configuration. Properties in the config/testApp namespace are only available to the instances of the service named "testApp".

Configuration is currently read on startup of the application. Sending a HTTP POST to /refresh will cause the configuration to be reloaded. Watching the configuration namespace (which Zookeeper supports) is not currently implemented, but will be a future addition to this project.

7.1 How to activate

Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-config will enable auto-configuration that will setup Spring Cloud Zookeeper Config.

7.2 Customizing

Zookeeper Config may be customized using the following properties:

bootstrap.yml.

spring:
  cloud:
    zookeeper:
      config:
        enabled: true
        root: configuration
        defaultContext: apps
        profileSeparator: '::'

enabled setting this value to "false" disables Zookeeper Config
root sets the base namespace for configuration values
defaultContext sets the name used by all applications
profileSeparator sets the value of the separator used to separate the profile name in property sources with profiles

7.3 ACLs

You can add authentication information for Zookeeper ACLs by calling the addAuthInfo method of a CuratorFramework bean. One way to accomplish this is by providing your own CuratorFramework bean:

@BoostrapConfiguration
public class CustomCuratorFrameworkConfig {

  @Bean
  public CuratorFramework curatorFramework() {
    CuratorFramework curator = new CuratorFramework();
    curator.addAuthInfo("digest", "user:password".getBytes());
    return curator;
  }

}

Consult the ZookeeperAutoConfiguration class to see how the CuratorFramework bean is configured by default.

Alternatively, you can add your credentials from a class that depends on the existing CuratorFramework bean:

@BoostrapConfiguration
public class DefaultCuratorFrameworkConfig {

  public ZookeeperConfig(CuratorFramework curator) {
    curator.addAuthInfo("digest", "user:password".getBytes());
  }

}

This must occur during the boostrapping phase. You can register configuration classes to run during this phase by annotating them with @BootstrapConfiguration and including them in a comma-separated list set as the value of the property org.springframework.cloud.bootstrap.BootstrapConfiguration in the file resources/META-INF/spring.factories:

resources/META-INF/spring.factories.

org.springframework.cloud.bootstrap.BootstrapConfiguration=\
my.project.CustomCuratorFrameworkConfig,\
my.project.DefaultCuratorFrameworkConfig