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Chapter 208. 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.
208.1. 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.
from("master:cheese:jms:foo").to("activemq:wine");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.
208.2. URI format
master:namespace:endpoint[?options]
Where endpoint is any Camel endpoint you want to run in master/slave mode.
208.3. 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:
master:namespace:delegateUri
with the following path and query parameters:
208.3.1. 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 |
208.3.2. 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 options 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 |
208.4. 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: ${file:name}")
.delay(delay)
.log(name + " - Done file: ${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
208.5. Implementations
Camel provide the following ClusterService implementations:
- camel-atomix
- camel-consul
- camel-file
- camel-kubernetes
- camel-zookeeper
208.6. See Also
- Configuring Camel
- Component
- Endpoint
- Getting Started
