Distributed Configuration with Zookeeper

Zookeeper provides a hierarchical namespace that lets clients 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, to mimic the Spring Cloud Config order of resolving properties. For example, an application with a name of testApp and with the dev profile has the following property sources created for it:

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 in the config/application namespace apply to all applications that use zookeeper for configuration. Properties in the config/testApp namespace are available only to the instances of the service named testApp.

Configuration is currently read on startup of the application. Sending a HTTP POST request to /refresh causes the configuration to be reloaded. Watching the configuration namespace (which Zookeeper supports) is also available.

Activating

Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-config enables autoconfiguration that sets up Spring Cloud Zookeeper Config.

When working with version 3.4 of Zookeeper you need to change the way you include the dependency as described here.

Spring Boot Config Data Import

Spring Boot 2.4 introduced a new way to import configuration data via the spring.config.import property. This is now the default way to get configuration from Zookeeper.

To optionally connect to Zookeeper for configuration set the following in application.properties:

application.properties

spring.config.import=optional:zookeeper:

This will connect to Zookeeper at the default location of "localhost:2181". Removing the optional: prefix will cause Zookeeper Config to fail if it is unable to connect to Zookeeper. To change the connection properties of Zookeeper Config either set spring.cloud.zookeeper.connect-string or add the connect string to the spring.config.import statement such as, spring.config.import=optional:zookeeper:myhost:2818. The location in the import property has precedence over the connect-string property.

Zookeeper Config will try to load values from four automatic contexts based on spring.cloud.zookeeper.config.name (which defaults to the value of the spring.application.name property) and spring.cloud.zookeeper.config.default-context (which defaults to application). If you want to specify the contexts rather than using the computed ones, you can add that information to the spring.config.import statement.

application.properties

spring.config.import=optional:zookeeper:myhost:2181/contextone;/context/two

This will optionally load configuration only from /contextone and /context/two.

A bootstrap file (properties or yaml) is not needed for the Spring Boot Config Data method of import via spring.config.import.

Customizing

Zookeeper Config may be customized by setting the following properties:

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.

If you have set spring.cloud.bootstrap.enabled=true or spring.config.use-legacy-processing=true, or included spring-cloud-starter-bootstrap, then the above values will need to be placed in bootstrap.yml instead of application.yml.

Access Control Lists (ACLs)

You can add authentication information for Zookeeper ACLs by calling the addAuthInfo method of a CuratorFramework bean. One way to accomplish this is to provide your own CuratorFramework bean, as shown in the following example:

@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’s default configuration.

Alternatively, you can add your credentials from a class that depends on the existing CuratorFramework bean, as shown in the following example:

@BoostrapConfiguration
public class DefaultCuratorFrameworkConfig {

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

}

The creation of this bean 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 that you set as the value of the org.springframework.cloud.bootstrap.BootstrapConfiguration property in the resources/META-INF/spring.factories file, as shown in the following example:

resources/META-INF/spring.factories

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