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

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 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 (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

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.

false

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

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.

false

boolean

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

lazyStartProducer (producer (advanced))

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

Message Headers

The JGroups raft component supports 12 message header(s), which is/are listed below:

Name Description Default Type

JGROUPSRAFT_LOG_SIZE (consumer)

Constant: HEADER_JGROUPSRAFT_LOG_SIZE

The Raft log size in number of entries.

int

JGROUPSRAFT_COMMIT_INDEX (consumer)

Constant: HEADER_JGROUPSRAFT_COMMIT_INDEX

The commit index.

int

JGROUPSRAFT_CURRENT_TERM (consumer)

Constant: HEADER_JGROUPSRAFT_CURRENT_TERM

The current raft term.

int

JGROUPSRAFT_IS_LEADER (consumer)

Constant: HEADER_JGROUPSRAFT_IS_LEADER

Whether the node is the Raft Leader or not.

boolean

JGROUPSRAFT_LAST_APPLIED (consumer)

Constant: HEADER_JGROUPSRAFT_LAST_APPLIED

The index of the last log entry that was appended to the log.

int

JGROUPSRAFT_LEADER_ADDRESS (consumer)

Constant: HEADER_JGROUPSRAFT_LEADER_ADDRESS

The Address ot Raft Leader or not.

Address

JGROUPSRAFT_RAFT_ID (consumer)

Constant: HEADER_JGROUPSRAFT_RAFT_ID

The Raft id of the node.

String

JGROUPSRAFT_EVENT_TYPE (consumer)

Constant: HEADER_JGROUPSRAFT_EVENT_TYPE

The event type.

Enum values:

  • LEADER

  • FOLLOWER

  • APPLY

  • READ_CONTENT_FROM

  • WRITE_CONTENT_TO

JGroupsRaftEventType

JGROUPSRAFT_SET_OFFSET (producer)

Constant: HEADER_JGROUPSRAFT_SET_OFFSET

Offset to use in the byte buffer to be set().

Integer

JGROUPSRAFT_SET_LENGTH (producer)

Constant: HEADER_JGROUPSRAFT_SET_LENGTH

Length to use in the byte buffer to be set().

Integer

JGROUPSRAFT_SET_TIMEOUT (producer)

Constant: HEADER_JGROUPSRAFT_SET_TIMEOUT

Timeout to be used in set() operation.

Long

JGROUPSRAFT_SET_TIMEUNIT (producer)

Constant: HEADER_JGROUPSRAFT_SET_TIMEUNIT

Timeunit to be used in set() operation.

Enum values:

  • NANOSECONDS

  • MICROSECONDS

  • MILLISECONDS

  • SECONDS

  • MINUTES

  • HOURS

  • DAYS

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 8 options, which are listed below.

Name Description Default Type

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 (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.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.raft.StateMachine type.

StateMachine
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