Chapter 358. 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.

358.1. 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.

358.2. URI format

zookeeper-master:name:endpoint[?options]

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

358.3. Options

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

NameDescriptionDefaultType

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:

358.3.1. Path Parameters (2 parameters):

NameDescriptionDefaultType

groupName

Required The name of the cluster group to use

 

String

consumerEndpointUri

Required The consumer endpoint to use in master/slave mode

 

String

358.3.2. Query Parameters (4 parameters):

NameDescriptionDefaultType

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

358.4. 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 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"