Clustering

Since Camel 2.20

Experimental feature

In Camel 2.20 we have introduced the following cluster related SPI:

  • Cluster Service

    A regular Camel service that manages cluster resources such as views (see below)

  • Cluster View

    Represent a view of the cluster with its own set of isolated resources. As today views provide supports for:

    • Leader Election

    • Topology events like members joining/leaving the cluster)

  • Cluster Member

    Represent a member of the cluster.

Cluster SPI Set-Up

A Cluster Service is just like any other camel service so set it up you only need to register your implementations to the camel context:

MyClusterServiceImpl service = new MyClusterServiceImpl();

context.addService(service);

The configuration of the Cluster Service depends on the implementation you have choosed. Out of the box camel provides the following implementations:

Type Module Class

atomix

camel-atomix

org.apache.camel.component.atomix.cluster.AtomixClusterService

consul

camel-consul

org.apache.camel.component.consul.cluster.ConsulClusterService

file

camel-core

org.apache.camel.component.file.cluster.FileLockClusterService

kubernetes

camel-kubernetes

org.apache.camel.component.kubernetes.cluster.KubernetesClusterService

zookeeper

camel-zookeeper

org.apache.camel.component.zookeeper.cluster.ZooKeeperClusterService

On Spring/Blueprint all the Cluster Service instances are automatically added to the camel context.

Configuration examples:

  • Spring Boot

    camel.component.file.cluster.service.enabled = true
camel.component.file.cluster.service.id = ${random.uuid}
camel.component.file.cluster.service.root = ${java.io.tmpdir}

  • Spring XML

    <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="
         http://www.springframework.org/schema/beans
         http://www.springframework.org/schema/beans/spring-beans.xsd
         http://camel.apache.org/schema/spring
         http://camel.apache.org/schema/spring/camel-spring.xsd">


  <bean id="zx" class="org.apache.camel.component.zookeeper.cluster.ZooKeeperClusterService">
    <property name="id" value="node-1"/>
    <property name="basePath" value="/camel/cluster"/>
    <property name="nodes" value="localhost:2181"/>
  </bean>

  <camelContext xmlns="http://camel.apache.org/schema/spring" autoStartup="false">
    ...
  </camelContext>

</beans>

Cluster SPI Usage

The Cluster SPI is leveraged by the folowing new implementations:

  • ClusteredRoutePolicy

    This is an implementation of a RoutePolicy that starts the routes it is associated to when the Cluster View it uses takes the leadership

    context.addRoutes(new RouteBuilder {
    @Override
    public void configure() throws Exception {
        // Create the route policy
        RoutePolicy policy = ClusteredRoutePolicy.forNamespace("my-ns");

        // bind the policy to one or more routes
        from("timer:clustered?delay=1000&period=1000")
            .routePolicy(policy)
            .log("Route ${routeId} is running ...");
    }
});

    To apply the same policy to all the rooutes a dedicated RoutePolicyFactory can be used:

    // add the clustered route policy factory to context
context.addRoutePolicyFactory(ClusteredRoutePolicyFactory.forNamespace("my-ns"));

context.addRoutes(new RouteBuilder {
    @Override
    public void configure() throws Exception {
        // bind the policy to one or more routes
        from("timer:clustered?delay=1000&period=1000")
            .log("Route ${routeId} is running ...");
    }
});

  • ClusteredRouteController

    This is an implementation of the RouteController SPI that lets the camel context start then starts/stops the routes when the leadership is taken/lost. This is well integrated with spring-boot apps so assuming you have tour routes set-up like:

    @Bean
public RouteBuilder routeBuilder() {
    return new RouteBuilder() {
        @Override
        public void configure() throws Exception {
            from("timer:heartbeat?period=10000")
                .routeId("heartbeat")
                .log("HeartBeat route (timer) ...");
            from("timer:clustered?period=5000")
                .routeId("clustered")
                .log("Clustered route (timer) ...");
        }
    };
}

    You can then leverage spring-boot configuration to make them clustered:

    # enable the route controller
camel.clustered.controller.enabled = true

# define the default namespace for routes
camel.clustered.controller.namespace = my-ns

# exlude the route with id 'heartbeat' from the clustered ones
camel.clustered.controller.routes[heartbeat].clustered = false

  • Master Component

    The master component is similar to a ClusteredRoutePolicy but it works on consumer level so it ensure the only a single endpoint in a cluster is consuming resources at any point in time. Set it up is very easy and all you need is to prefix singleton endpoints according to the master component syntax:

    master:namespace:delegateUri

    A concrete example:

    @Bean
public RouteBuilder routeBuilder() {
    return new RouteBuilder() {
        @Override
        public void configure() throws Exception {
            from("timer:heartbeat?period=10000")
                .routeId("heartbeat")
                .log("HeartBeat route (timer) ...");
            from("master:my-ns:timer:clustered?period=5000")
                .routeId("clustered")
                .log("Clustered route (timer) ...");
        }
    };
}
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