Spring Cloud Zookeeper

Table of Contents

1. Install Zookeeper
2. Service Discovery with Zookeeper
2.1. How to activate
2.2. Registering with Zookeeper
2.3. Using the DiscoveryClient
3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components
3.1. Ribbon with Zookeeper
4. Spring Cloud Zookeeper and Service Registry
4.1. Instance Status
5. Zookeeper Dependencies
5.1. Using the Zookeeper Dependencies
5.2. How to activate Zookeeper Dependencies
5.3. Setting up Zookeeper Dependencies
5.3.1. Aliases
5.3.2. Path
5.3.3. Load balancer type
5.3.4. Content-Type template and version
5.3.5. Default headers
5.3.6. Obligatory dependencies
5.3.7. Stubs
5.4. Configuring Spring Cloud Zookeeper Dependencies
6. Spring Cloud Zookeeper Dependency Watcher
6.1. How to activate
6.2. Registering a listener
6.3. Presence Checker
7. Distributed Configuration with Zookeeper
7.1. How to activate
7.2. Customizing
7.3. ACLs

This project provides Zookeeper integrations for Spring Boot apps through autoconfiguration and binding to the Spring Environment and other Spring programming model idioms. With a few simple annotations you can quickly enable and configure the common patterns inside your application and build large distributed systems with Zookeeper based components. The patterns provided include Service Discovery and Configuration. Intelligent Routing (Zuul) and Client Side Load Balancing (Ribbon), Circuit Breaker (Hystrix) are provided by integration with Spring Cloud Netflix.

1. Install Zookeeper

Please see the installation documentation for instructions on how to install Zookeeper.

2. Service Discovery with Zookeeper

Service Discovery is one of the key tenets of a microservice based architecture. Trying to hand configure each client or some form of convention can be very difficult to do and can be very brittle. Curator(A java library for Zookeeper) provides Service Discovery services via Service Discovery Extension. Spring Cloud Zookeeper leverages this extension for service registration and discovery.

2.1 How to activate

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


You still need to include org.springframework.boot:spring-boot-starter-web for web functionality.

2.2 Registering with Zookeeper

When a client registers with Zookeeper, it provides meta-data about itself such as host and port, id and name.

Example Zookeeper client:

public class Application {

    public String home() {
        return "Hello world";

    public static void main(String[] args) {
        new SpringApplicationBuilder(Application.class).web(true).run(args);


(i.e. utterly normal Spring Boot app). If Zookeeper is located somewhere other than localhost:2181, the configuration is required to locate the server. Example:


      connect-string: localhost:2181


If you use Spring Cloud Zookeeper Config, the above values will need to be placed in bootstrap.yml instead of application.yml.

The default service name, instance id and port, taken from the Environment, are ${spring.application.name}, the Spring Context ID and ${server.port} respectively.

Having spring-cloud-starter-zookeeper-discovery on the classpath makes the app into both a Zookeeper "service" (i.e. it registers itself) and a "client" (i.e. it can query Zookeeper to locate other services).

If you would like to disable the Zookeeper Discovery Client you can set spring.cloud.zookeeper.discovery.enabled to false.

2.3 Using the DiscoveryClient

Spring Cloud has support for Feign (a REST client builder) and also Spring RestTemplate using the logical service names instead of physical URLs.

You can also use the org.springframework.cloud.client.discovery.DiscoveryClient which provides a simple API for discovery clients that is not specific to Netflix, e.g.

private DiscoveryClient discoveryClient;

public String serviceUrl() {
    List<ServiceInstance> list = discoveryClient.getInstances("STORES");
    if (list != null && list.size() > 0 ) {
        return list.get(0).getUri().toString();
    return null;

3. Using Spring Cloud Zookeeper with Spring Cloud Netflix Components

Spring Cloud Netflix supplies useful tools that work regardless of which DiscoveryClient implementation is used. Feign, Turbine, Ribbon and Zuul all work with Spring Cloud Zookeeper.

3.1 Ribbon with Zookeeper

Spring Cloud Zookeeper provides an implementation of Ribbon’s ServerList. When the spring-cloud-starter-zookeeper-discovery is used, Ribbon is auto-configured to use the ZookeeperServerList by default.

4. Spring Cloud Zookeeper and Service Registry

Spring Cloud Zookeeper implements the ServiceRegistry interface allowing developers to register arbitrary service in a programmatic way.

The ServiceInstanceRegistration class offers a builder() method to create a Registration object that can be used by the ServiceRegistry.

private ZookeeperServiceRegistry serviceRegistry;

public void registerThings() {
    ZookeeperRegistration registration = ServiceInstanceRegistration.builder()

4.1 Instance Status

Netflix Eureka supports having instances registered with the server that are OUT_OF_SERVICE and not returned as active service instances. This is very useful for behaviors such as blue/green deployments. The Curator Service Discovery recipe does not support this behavior. Taking advantage of the flexible payload has let Spring Cloud Zookeeper implement OUT_OF_SERVICE by updating some specific metadata and then filtering on that metadata in the Ribbon ZookeeperServerList. The ZookeeperServerList filters out all non-null instance statuses that do not equal UP. If the instance status field is empty, it is considered UP for backwards compatibility. To change the status of an instance POST OUT_OF_SERVICE to the ServiceRegistry instance status actuator endpoint.

$ echo -n OUT_OF_SERVICE | http POST http://localhost:8081/service-registry/instance-status
NOTE: The above example uses the `http` command from https://httpie.org

5. Zookeeper Dependencies

5.1 Using the Zookeeper Dependencies

Spring Cloud Zookeeper gives you a possibility to provide dependencies of your application as properties. As dependencies you can understand other applications that are registered in Zookeeper and which you would like to call via Feign (a REST client builder) and also Spring RestTemplate.

You can also benefit from the Zookeeper Dependency Watchers functionality that lets you control and monitor what is the state of your dependencies and decide what to do with that.

5.2 How to activate Zookeeper Dependencies

  • Including a dependency on org.springframework.cloud:spring-cloud-starter-zookeeper-discovery will enable auto-configuration that will setup Spring Cloud Zookeeper Dependencies.
  • If you have to have the spring.cloud.zookeeper.dependencies section properly set up - check the subsequent section for more details then the feature is active
  • You can have the dependencies turned off even if you’ve provided the dependencies in your properties. Just set the property spring.cloud.zookeeper.dependency.enabled to false (defaults to true).

5.3 Setting up Zookeeper Dependencies

Let’s take a closer look at an example of dependencies representation:


spring.application.name: yourServiceName
      path: /path/where/newsletter/has/registered/in/zookeeper
      loadBalancerType: ROUND_ROBIN
      contentTypeTemplate: application/vnd.newsletter.$version+json
      version: v1
            - value1
            - value2
      required: false
      stubs: org.springframework:foo:stubs
      path: /path/where/mailing/has/registered/in/zookeeper
      loadBalancerType: ROUND_ROBIN
      contentTypeTemplate: application/vnd.mailing.$version+json
      version: v1
      required: true

Let’s now go through each part of the dependency one by one. The root property name is spring.cloud.zookeeper.dependencies.

5.3.1 Aliases

Below the root property you have to represent each dependency has by an alias due to the constraints of Ribbon (the application id has to be placed in the URL thus you can’t pass any complex path like /foo/bar/name). The alias will be the name that you will use instead of serviceId for DiscoveryClient, Feign or RestTemplate.

In the aforementioned examples the aliases are newsletter and mailing. Example of Feign usage with newsletter would be:

public interface NewsletterService {
        @RequestMapping(method = RequestMethod.GET, value = "/newsletter")
        String getNewsletters();

5.3.2 Path

Represented by path yaml property.

Path is the path under which the dependency is registered under Zookeeper. Like presented before Ribbon operates on URLs thus this path is not compliant with its requirement. That is why Spring Cloud Zookeeper maps the alias to the proper path.

5.3.3 Load balancer type

Represented by loadBalancerType yaml property.

If you know what kind of load balancing strategy has to be applied when calling this particular dependency then you can provide it in the yaml file and it will be automatically applied. You can choose one of the following load balancing strategies

  • STICKY - once chosen the instance will always be called
  • RANDOM - picks an instance randomly
  • ROUND_ROBIN - iterates over instances over and over again

5.3.4 Content-Type template and version

Represented by contentTypeTemplate and version yaml property.

If you version your api via the Content-Type header then you don’t want to add this header to each of your requests. Also if you want to call a new version of the API you don’t want to roam around your code to bump up the API version. That’s why you can provide a contentTypeTemplate with a special $version placeholder. That placeholder will be filled by the value of the version yaml property. Let’s take a look at an example.

Having the following contentTypeTemplate:


and the following version:


Will result in setting up of a Content-Type header for each request:


5.3.5 Default headers

Represented by headers map in yaml

Sometimes each call to a dependency requires setting up of some default headers. In order not to do that in code you can set them up in the yaml file. Having the following headers section:

        - text/html
        - application/xhtml+xml
        - no-cache

Results in adding the Accept and Cache-Control headers with appropriate list of values in your HTTP request.

5.3.6 Obligatory dependencies

Represented by required property in yaml

If one of your dependencies is required to be up and running when your application is booting then it’s enough to set up the required: true property in the yaml file.

If your application can’t localize the required dependency during boot time it will throw an exception and the Spring Context will fail to set up. In other words your application won’t be able to start if the required dependency is not registered in Zookeeper.

You can read more about Spring Cloud Zookeeper Presence Checker in the following sections.

5.3.7 Stubs

You can provide a colon separated path to the JAR containing stubs of the dependency. Example

stubs: org.springframework:foo:stubs

means that for a particular dependencies can be found under:

  • groupId: org.springframework
  • artifactId: foo
  • classifier: stubs - this is the default value

This is actually equal to

stubs: org.springframework:foo

since stubs is the default classifier.

5.4 Configuring Spring Cloud Zookeeper Dependencies

There is a bunch of properties that you can set to enable / disable parts of Zookeeper Dependencies functionalities.

  • spring.cloud.zookeeper.dependencies - if you don’t set this property you won’t benefit from Zookeeper Dependencies
  • spring.cloud.zookeeper.dependency.ribbon.enabled (enabled by default) - Ribbon requires explicit global configuration or a particular one for a dependency. By turning on this property runtime load balancing strategy resolution is possible and you can profit from the loadBalancerType section of the Zookeeper Dependencies. The configuration that needs this property has an implementation of LoadBalancerClient that delegates to the ILoadBalancer presented in the next bullet
  • spring.cloud.zookeeper.dependency.ribbon.loadbalancer (enabled by default) - thanks to this property the custom ILoadBalancer knows that the part of the URI passed to Ribbon might actually be the alias that has to be resolved to a proper path in Zookeeper. Without this property you won’t be able to register applications under nested paths.
  • spring.cloud.zookeeper.dependency.headers.enabled (enabled by default) - this property registers such a RibbonClient that automatically will append appropriate headers and content types with version as presented in the Dependency configuration. Without this setting of those two parameters will not be operational.
  • spring.cloud.zookeeper.dependency.resttemplate.enabled (enabled by default) - when enabled will modify the request headers of @LoadBalanced annotated RestTemplate so that it passes headers and content type with version set in Dependency configuration. Wihtout this setting of those two parameters will not be operational.

6. Spring Cloud Zookeeper Dependency Watcher

The Dependency Watcher mechanism allows you to register listeners to your dependencies. The functionality is in fact an implementation of the Observator pattern. When a dependency changes its state (UP or DOWN) then some custom logic can be applied.

6.1 How to activate

Spring Cloud Zookeeper Dependencies functionality needs to be enabled to profit from Dependency Watcher mechanism.

6.2 Registering a listener

In order to register a listener you have to implement an interface org.springframework.cloud.zookeeper.discovery.watcher.DependencyWatcherListener and register it as a bean. The interface gives you one method:

    void stateChanged(String dependencyName, DependencyState newState);

If you want to register a listener for a particular dependency then the dependencyName would be the discriminator for your concrete implementation. newState will provide you with information whether your dependency has changed to CONNECTED or DISCONNECTED.

6.3 Presence Checker

Bound with Dependency Watcher is the functionality called Presence Checker. It allows you to provide custom behaviour upon booting of your application to react accordingly to the state of your dependencies.

The default implementation of the abstract org.springframework.cloud.zookeeper.discovery.watcher.presence.DependencyPresenceOnStartupVerifier class is the org.springframework.cloud.zookeeper.discovery.watcher.presence.DefaultDependencyPresenceOnStartupVerifier which works in the following way.

  • If the dependency is marked us required and it’s not in Zookeeper then upon booting your application will throw an exception and shutdown
  • If dependency is not required the org.springframework.cloud.zookeeper.discovery.watcher.presence.LogMissingDependencyChecker will log that application is missing at WARN level

The functionality can be overriden since the DefaultDependencyPresenceOnStartupVerifier is registered only when there is no bean of DependencyPresenceOnStartupVerifier.

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:


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:


        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:

public class CustomCuratorFrameworkConfig {

  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:

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: