Chapter 219. Master Component
Chapter 219. Master Component Available as of Camel version 2.20 The camel-master: endpoint provides a way to ensure only a single consumer in a cluster consumes from a given endpoint; with automatic failover if that JVM dies. This can be very useful if you need to consume from some legacy back end which either doesn't support concurrent consumption or due to commercial or stability reasons you can only have a single connection at any point in time. 219.1. Using the master endpoint Just prefix any camel endpoint with master:someName: where someName is a logical name and is used to acquire the master lock. e.g. The above simulates the [Exclusive Consumers]( http://activemq.apache.org/exclusive-consumer.html ) type feature in ActiveMQ; but on any third party JMS provider which maybe doesn't support exclusive consumers. 219.2. URI format Where endpoint is any Camel endpoint you want to run in master/slave mode. 219.3. Options The Master component supports 3 options, which are listed below. Name Description Default Type service (advanced) Inject the service to use. CamelClusterService serviceSelector (advanced) Inject the service selector used to lookup the CamelClusterService to use. Selector resolveProperty Placeholders (advanced) Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. true boolean The Master endpoint is configured using URI syntax: with the following path and query parameters: 219.3.1. Path Parameters (2 parameters): Name Description Default Type namespace Required The name of the cluster namespace to use String delegateUri Required The endpoint uri to use in master/slave mode String 219.3.2. Query Parameters (4 parameters): Name Description Default Type bridgeErrorHandler (consumer) Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. false boolean exceptionHandler (consumer) To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. ExceptionHandler exchangePattern (consumer) Sets the exchange pattern when the consumer creates an exchange. ExchangePattern synchronous (advanced) Sets whether synchronous processing should be strictly used, or Camel is allowed to use asynchronous processing (if supported). false boolean 219.4. Spring Boot Auto-Configuration The component supports 4 options, which are listed below. Name Description Default Type camel.component.master.enabled Whether to enable auto configuration of the master component. This is enabled by default. Boolean camel.component.master.resolve-property-placeholders Whether the component should resolve property placeholders on itself when starting. Only properties which are of String type can use property placeholders. true Boolean camel.component.master.service Inject the service to use. The option is a org.apache.camel.cluster.CamelClusterService type. String camel.component.master.service-selector Inject the service selector used to lookup the CamelClusterService to use. The option is a org.apache.camel.cluster.CamelClusterService.Selector type. String 219.5. Example You can protect a clustered Camel application to only consume files from one active node. // the file endpoint we want to consume from String url = "file:target/inbox?delete=true"; // use the camel master component in the clustered group named myGroup // to run a master/slave mode in the following Camel url from("master:myGroup:" + url) .log(name + " - Received file: USD{file:name}") .delay(delay) .log(name + " - Done file: USD{file:name}") .to("file:target/outbox"); The master component leverages CamelClusterService you can configure using Java ZooKeeperClusterService service = new ZooKeeperClusterService(); service.setId("camel-node-1"); service.setNodes("myzk:2181"); service.setBasePath("/camel/cluster"); context.addService(service) Xml (Spring/Blueprint) <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="cluster" class="org.apache.camel.component.zookeeper.cluster.ZooKeeperClusterService"> <property name="id" value="camel-node-1"/> <property name="basePath" value="/camel/cluster"/> <property name="nodes" value="myzk:2181"/> </bean> <camelContext xmlns="http://camel.apache.org/schema/spring" autoStartup="false"> ... </camelContext> </beans> Spring boot camel.component.zookeeper.cluster.service.enabled = true camel.component.zookeeper.cluster.service.id = camel-node-1 camel.component.zookeeper.cluster.service.base-path = /camel/cluster camel.component.zookeeper.cluster.service.nodes = myzk:2181 219.6. Implementations Camel provide the following ClusterService implementations: camel-atomix camel-consul camel-file camel-kubernetes camel-zookeeper 219.7. See Also Configuring Camel Component Endpoint Getting Started
from("master:cheese:jms:foo").to("activemq:wine"); master:namespace:endpoint[?options] master:namespace:delegateUri // the file endpoint we want to consume from String url = "file:target/inbox?delete=true"; // use the camel master component in the clustered group named myGroup // to run a master/slave mode in the following Camel url from("master:myGroup:" + url) .log(name + " - Received file: USD{file:name}") .delay(delay) .log(name + " - Done file: USD{file:name}") .to("file:target/outbox"); ZooKeeperClusterService service = new ZooKeeperClusterService(); service.setId("camel-node-1"); service.setNodes("myzk:2181"); service.setBasePath("/camel/cluster"); context.addService(service) <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="cluster" class="org.apache.camel.component.zookeeper.cluster.ZooKeeperClusterService"> <property name="id" value="camel-node-1"/> <property name="basePath" value="/camel/cluster"/> <property name="nodes" value="myzk:2181"/> </bean> <camelContext xmlns="http://camel.apache.org/schema/spring" autoStartup="false"> </camelContext> </beans> camel.component.zookeeper.cluster.service.enabled = true camel.component.zookeeper.cluster.service.id = camel-node-1 camel.component.zookeeper.cluster.service.base-path = /camel/cluster camel.component.zookeeper.cluster.service.nodes = myzk:2181