ZooKeeper Master Component

Available as of Camel version 2.19

The zookeeper-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.

Using the master endpoint

Just prefix any camel endpoint with zookeeper-master:someName: where someName is a logical name and is used to acquire the master lock. e.g.

from("zookeeper-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.

URI format

zookeeper-master:name:endpoint[?options]

Where endpoint is any Camel endpoint you want to run in master/slave mode.

Options

The ZooKeeper Master component supports 7 options, which are listed below.

Name Description Default Type

containerIdFactory (consumer)

To use a custom ContainerIdFactory for creating container ids.

ContainerIdFactory

zkRoot (consumer)

The root path to use in zookeeper where information is stored which nodes are master/slave etc. Will by default use: /camel/zookeepermaster/clusters/master

/camel/zookeepermaster/clusters/master

String

curator (advanced)

To use a custom configured CuratorFramework as connection to zookeeper ensemble.

CuratorFramework

maximumConnection Timeout (consumer)

Timeout in millis to use when connecting to the zookeeper ensemble

10000

int

zooKeeperUrl (consumer)

The url for the zookeeper ensemble

localhost:2181

String

zooKeeperPassword (security)

The password to use when connecting to the zookeeper ensemble

String

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 ZooKeeper Master endpoint is configured using URI syntax:

zookeeper-master:groupName:consumerEndpointUri

with the following path and query parameters:

Path Parameters (2 parameters):

Name Description Default Type

groupName

Required The name of the cluster group to use

String

consumerEndpointUri

Required The consumer endpoint to use in master/slave mode

String

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

Spring Boot Auto-Configuration

When using Spring Boot make sure to use the following Maven dependency to have support for auto configuration:

<dependency>
  <groupId>org.apache.camel</groupId>
  <artifactId>camel-zookeeper-master-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 8 options, which are listed below.

Name Description Default Type

camel.component.zookeeper-master.container-id-factory

To use a custom ContainerIdFactory for creating container ids. The option is a org.apache.camel.component.zookeepermaster.ContainerIdFactory type.

String

camel.component.zookeeper-master.curator

To use a custom configured CuratorFramework as connection to zookeeper ensemble. The option is a org.apache.curator.framework.CuratorFramework type.

String

camel.component.zookeeper-master.enabled

Enable zookeeper-master component

true

Boolean

camel.component.zookeeper-master.maximum-connection-timeout

Timeout in millis to use when connecting to the zookeeper ensemble

10000

Integer

camel.component.zookeeper-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.zookeeper-master.zk-root

The root path to use in zookeeper where information is stored which nodes are master/slave etc. Will by default use: /camel/zookeepermaster/clusters/master

/camel/zookeepermaster/clusters/master

String

camel.component.zookeeper-master.zoo-keeper-password

The password to use when connecting to the zookeeper ensemble

String

camel.component.zookeeper-master.zoo-keeper-url

The url for the zookeeper ensemble

localhost:2181

String

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 zookeeper master component in the clustered group named myGroup
    // to run a master/slave mode in the following Camel url
    from("zookeeper-master:myGroup:" + url)
        .log(name + " - Received file: ${file:name}")
        .delay(delay)
        .log(name + " - Done file:     ${file:name}")
        .to("file:target/outbox");

ZooKeeper will by default connect to localhost:2181, but you can configure this on the component level.

    MasterComponent master = new MasterComponent();
    master.setZooKeeperUrl("myzookeeper:2181");

However you can also configure the url of the ZooKeeper ensemble using environment variables.

export ZOOKEEPER_URL = "myzookeeper:2181"

Master RoutePolicy

You can also use a RoutePolicy to control routes in master/slave mode.

When doing so you must configure the route policy with

  • url to zookeeper ensemble

  • name of cluster group

  • important and set the route to not auto startup

A little example

    MasterRoutePolicy master = new MasterRoutePolicy();
    master.setZooKeeperUrl("localhost:2181");
    master.setGroupName("myGroup");

    // its import to set the route to not auto startup
    // as we let the route policy start/stop the routes when it becomes a master/slave etc
    from("file:target/inbox?delete=true").noAutoStartup()
        // use the zookeeper master route policy in the clustered group
        // to run this route in master/slave mode
        .routePolicy(master)
        .log(name + " - Received file: ${file:name}")
        .delay(delay)
        .log(name + " - Done file:     ${file:name}")
        .to("file:target/outbox");