JGroups raft

Since Camel 2.24

Both producer and consumer are supported

JGroups-raft is a Raft implementation in JGroups. The jgroups-raft: component provides interoperability between camel and a JGroups-raft clusters.

Maven users will need to add the following dependency to their pom.xml for this component.

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-jgroups-raft</artifactId>
    <!-- use the same version as your Camel core version -->
    <version>x.y.z</version>
</dependency>

URI format

jgroups-raft:clusterName[?options]

Where clusterName represents the name of the JGroups-raft cluster the component should connect to.

Options

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. 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.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL as a type safe way of configuring endpoints.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

Component Options

The JGroups raft component supports 7 options, which are listed below.

Name Description Default Type

channelProperties (common)

Specifies configuration properties of the RaftHandle JChannel used by the endpoint (ignored if raftHandle ref is provided).

raft.xml

String

raftHandle (common)

RaftHandle to use.

RaftHandle

raftId (common)

Required Unique raftId to use.

String

stateMachine (common)

StateMachine to use.

NopStateMachine

StateMachine

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.

boolean

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

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

Endpoint Options

The JGroups raft endpoint is configured using URI syntax:

jgroups-raft:clusterName

with the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

clusterName (common)

Required The name of the JGroupsraft cluster the component should connect to.

String

Query Parameters (5 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.

boolean

enableRoleChangeEvents (consumer)

If set to true, the consumer endpoint will receive roleChange event as well (not just connecting and/or using the state machine). By default it is set to 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

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

boolean

Headers

Header Constant Since version

Description

JGROUPSRAFT_COMMIT_INDEX

JGroupsRaftEndpoint.HEADER_JGROUPSRAFT_COMMIT_INDEX

Consumer : The commit index (int).

JGROUPSRAFT_CURRENT_TERM

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_CURRENT_TERM

Consumer : The current raft term (int).

JGROUPSRAFT_IS_LEADER

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_IS_LEADER

Consumer: Whether the node is the Raft Leader or not (boolean).

JGROUPSRAFT_LAST_APPLIED

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_LAST_APPLIED

Consumer: The index of the last log entry that was appended to the log (int).

JGROUPSRAFT_LEADER_ADDRESS

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_LEADER_ADDRESS

Consumer: The Address ot Raft Leader or not (org.jgroups.Address).

JGROUPSRAFT_LOG_SIZE

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_LOG_SIZE

Consumer: The Raft log size in number of entries (int).

JGROUPSRAFT_LOG_SIZE_BYTE

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_LOG_SIZE_BYTE

Consumer: The Raft log size in bytes (int).

JGROUPSRAFT_RAFT_ID

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_RAFT_ID

Consumer: The Raft id of the node (String).

JGROUPSRAFT_EVENT_TYPE

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_EVENT_TYPE

Consumer: The event type, one of org.apache.camel.component.jgroups.raft.JGroupsRaftEventType ENUM.

JGROUPSRAFT_SET_OFFSET

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_SET_OFFSET

Producer: Offset to use in the byte[] buffer to be set().

JGROUPSRAFT_SET_LENGTH

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_SET_LENGTH

Producer: Length to use in the byte[] buffer to be set().

JGROUPSRAFT_SET_TIMEOUT

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_SET_TIMEOUT

Producer: Timeout to be used in set() operation.

JGROUPSRAFT_SET_TIMEUNIT

JGroupsRaftEndpoint.`HEADER_JGROUPSRAFT_SET_TIMEUNIT

Usage

Using jgroups-raft component with enableRoleChangeEvents=true on the consumer side of the route will capture change in JGroups-raft role and forward them to the Camel route. JGroups-raft consumer processes incoming messages asynchronously.

// Capture raft role changes from cluster named
// 'clusterName' and send them to Camel route.
from("jgroups-raft:clusterName?enableRoleChangeEvents=true").to("seda:queue");

Using jgroups-raft component on the producer side of the route will use the body of the camel exchange (which must be a byte[]) to perform a setX() operation on the raftHandle associated with the endpoint..

// perform a setX() operation to the cluster named 'clusterName' shared state machine
from("direct:start").to("jgroups-raft:clusterName");

Examples

Receive cluster view change notifications

The snippet below demonstrates how to create the consumer endpoint listening to the change role events. By default this option is off.

...
from("jgroups-raft:clusterName?enableRoleChangeEvents=true").to(mock:mockEndpoint);
...

Keeping singleton route within the cluster

The snippet below demonstrates how to keep the singleton consumer route in the cluster of Camel Contexts. As soon as the master node dies, one of the slaves will be elected as a new master and started. In this particular example we want to keep singleton jetty instance listening for the requests on address` http://localhost:8080/orders`.

JGroupsRaftClusterService service = new JGroupsRaftClusterService();
service.setId("raftId");
service.setRaftId("raftId");
service.setJgroupsClusterName("clusterName");
...
context.addService(service);

from("master:mycluster:jetty:http://localhost:8080/orders").to("jms:orders");

Spring Boot Auto-Configuration

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

The component supports 13 options, which are listed below.

Name Description Default Type

camel.cluster.jgroups-raft.enabled

Sets if the jgroups raft cluster service should be enabled or not, default is false.

false

Boolean

camel.cluster.jgroups-raft.id

Cluster Service ID

String

camel.cluster.jgroups-raft.jgroups-raft-cluster-name

JGroups Cluster name

String

camel.cluster.jgroups-raft.jgroups-raft-config

JGrups-raft configuration File name

String

camel.cluster.jgroups-raft.raft-id

JGroups-raft ID

String

camel.component.jgroups-raft.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.jgroups-raft.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.jgroups-raft.channel-properties

Specifies configuration properties of the RaftHandle JChannel used by the endpoint (ignored if raftHandle ref is provided).

raft.xml

String

camel.component.jgroups-raft.enabled

Whether to enable auto configuration of the jgroups-raft component. This is enabled by default.

Boolean

camel.component.jgroups-raft.lazy-start-producer

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

Boolean

camel.component.jgroups-raft.raft-handle

RaftHandle to use. The option is a org.jgroups.raft.RaftHandle type.

RaftHandle

camel.component.jgroups-raft.raft-id

Unique raftId to use.

String

camel.component.jgroups-raft.state-machine

StateMachine to use. The option is a org.jgroups.protocols.raft.StateMachine type.

StateMachine
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