ZooKeeper Master

Since Camel 2.19

Only consumer is supported

The zookeeper-master: endpoint provides a way to ensure only a single consumer in a cluster consumes from a given endpoint; with automatic fails over if that JVM dies.

This can be beneficial if you need to consume from some legacy back end that 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

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 that 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.

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

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.

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.

Component Options

The ZooKeeper Master component supports 8 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 (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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

maximumConnectionTimeout (consumer)

Timeout in millis to use when connecting to the zookeeper ensemble.

10000

int

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

zooKeeperUrl (consumer)

The url for the zookeeper ensemble.

localhost:2181

String

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

containerIdFactory (advanced)

To use a custom ContainerIdFactory for creating container ids.

ContainerIdFactory

curator (advanced)

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

CuratorFramework

zooKeeperPassword (security)

The password to use when connecting to the zookeeper ensemble.

String

Endpoint Options

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 (consumer)

Required The name of the cluster group to use.

String

consumerEndpointUri (consumer)

Required The consumer endpoint to use in master/slave mode.

String

Query Parameters (3 parameters)

Name Description Default Type

bridgeErrorHandler (consumer (advanced))

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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

ExchangePattern

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 the 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");

Spring Boot Auto-Configuration

When using zookeeper-master with 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-zookeeper-master-starter</artifactId>
  <version>x.x.x</version>
  <!-- use the same version as your Camel core version -->
</dependency>

The component supports 9 options, which are listed below.

Name Description Default Type

camel.component.zookeeper-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.zookeeper-master.bridge-error-handler

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. 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.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.

ContainerIdFactory

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.

CuratorFramework

camel.component.zookeeper-master.enabled

Whether to enable auto configuration of the zookeeper-master component. This is enabled by default.

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.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
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