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78. 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 not currently implemented.
78.1 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.
78.2 Customizing
Zookeeper Config may be customized by setting the following properties:
bootstrap.yml.
spring:
cloud:
zookeeper:
config:
enabled: true
root: configuration
defaultContext: apps
profileSeparator: '::'
enabled
: Setting this value tofalse
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.
78.3 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