Chapter 96. Master Only consumer is supported 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. 96.1. Dependencies When using master with Red Hat build of Camel Spring Boot make sure to use the following Maven dependency to have support for auto configuration: <dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-master-starter</artifactId> </dependency> 96.2. 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. from("master:cheese:jms:foo").to("activemq:wine"); In this example, there master component ensures that the route is only active in one node, at any given time, in the cluster. So if there are 8 nodes in the cluster, then the master component will elect one route to be the leader, and only this route will be active, and hence only this route will consume messages from jms:foo . In case this route is stopped or unexpected terminated, then the master component will detect this, and re-elect another node to be active, which will then become active and start consuming messages from jms:foo . Note Apache ActiveMQ 5.x has such feature out of the box called Exclusive Consumers . 96.3. URI format Where endpoint is any Camel endpoint you want to run in master/slave mode. 96.4. Configuring Options Camel components are configured on two separate levels: component level endpoint level 96.4.1. Configuring Component Options At the component level, you set general and shared configurations that are, then, inherited by the endpoints. It is the highest configuration level. For example, a component may have security settings, credentials for authentication, urls for network connection and so forth. Some components only have a few options, and others may have many. Because components typically have pre-configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all. You can configure components using: the Component DSL . in a configuration file (application.properties, *.yaml files, etc). directly in the Java code. 96.4.2. Configuring Endpoint Options You usually spend more time setting up endpoints because they have many options. These options help you customize what you want the endpoint to do. The options are also categorized into whether the endpoint is used as a consumer (from), as a producer (to), or both. Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java. A good practice when configuring options is to use Property Placeholders . Property placeholders provide a few benefits: They help prevent using hardcoded urls, port numbers, sensitive information, and other settings. They allow externalizing the configuration from the code. They help the code to become more flexible and reusable. The following two sections list all the options, firstly for the component followed by the endpoint. 96.5. Component Options The Master component supports 4 options, which are listed below. 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 autowiredEnabled (advanced) Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true boolean service (advanced) Inject the service to use. CamelClusterService serviceSelector (advanced) Inject the service selector used to lookup the CamelClusterService to use. Selector 96.6. Endpoint Options The Master endpoint is configured using URI syntax: with the following path and query parameters: 96.6.1. Path Parameters (2 parameters) Name Description Default Type namespace (consumer) Required The name of the cluster namespace to use. String delegateUri (consumer) Required The endpoint uri to use in master/slave mode. String 96.6.2. Query Parameters (3 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 (advanced)) 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 (advanced)) Sets the exchange pattern when the consumer creates an exchange. Enum values: InOnly InOut InOptionalOut ExchangePattern 96.7. 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 96.8. Implementations Camel provides the following ClusterService implementations: camel-consul camel-file camel-infinispan camel-jgroups-raft camel-jgroups camel-kubernetes camel-zookeeper 96.9. Spring Boot Auto-Configuration The component supports 5 options, which are listed below. Name Description Default Type camel.component.master.autowired-enabled Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. true Boolean camel.component.master.bridge-error-handler 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 camel.component.master.enabled Whether to enable auto configuration of the master component. This is enabled by default. Boolean camel.component.master.service Inject the service to use. The option is a org.apache.camel.cluster.CamelClusterService type. CamelClusterService 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. CamelClusterServiceUSDSelector

Commands:
<dependency> <groupId>org.apache.camel.springboot</groupId> <artifactId>camel-master-starter</artifactId> </dependency>
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