JGroups

Since Camel 2.13

Both producer and consumer are supported

JGroups is a toolkit for reliable multicast communication. The jgroups: component provides exchange of messages between Camel infrastructure and JGroups 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</artifactId>
    <!-- use the same version as your Camel core version -->
    <version>x.y.z</version>
</dependency>

URI format 

jgroups:clusterName[?options]

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

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 component supports the following options which are listed below.

Name Description Default Type

channel (common)

Channel to use.

JChannel

channelProperties (common)

Specifies configuration properties of the JChannel used by the endpoint.

String

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

enableViewMessages (consumer)

If set to true, the consumer endpoint will receive org.jgroups.View messages as well (not only org.jgroups.Message instances). By default only regular messages are consumed by the endpoint.

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

deserializationFilter (security)

Sets an ObjectInputFilter pattern (jdk.serialFilter syntax) applied as a defense-in-depth check on the class of the message body deserialized by org.jgroups.Message.getObject(). The pattern is evaluated after JGroups has deserialized the payload, so this option alone does not prevent gadget-chain execution that happens inside the JGroups receive path; to block such attacks, also configure the JVM-wide -Djdk.serialFilter and secure the channel with AUTH and encryption. When this option is not set and no JVM-wide filter is configured, a conservative default filter denying java.net. and otherwise allowing java., javax. and org.apache.camel. is applied. Use to accept any type.

String

Endpoint Options

The JGroups endpoint is configured using URI syntax: 

jgroups:clusterName

With the following path and query parameters:

Path Parameters

Name Description Default Type

clusterName (common)

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

String

Query Parameters

Name Description Default Type

channelProperties (common)

Specifies configuration properties of the JChannel used by the endpoint.

String

enableViewMessages (consumer)

If set to true, the consumer endpoint will receive org.jgroups.View messages as well (not only org.jgroups.Message instances). By default only regular messages are consumed by the endpoint.

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

deserializationFilter (security)

Sets an ObjectInputFilter pattern (jdk.serialFilter syntax) applied as a defense-in-depth check on the class of the message body deserialized by org.jgroups.Message.getObject(). The pattern is evaluated after JGroups has deserialized the payload, so this option alone does not prevent gadget-chain execution that happens inside the JGroups receive path; to block such attacks, also configure the JVM-wide -Djdk.serialFilter and secure the channel with AUTH and encryption. When this option is not set and no JVM-wide filter is configured, a conservative default filter denying java.net. and otherwise allowing java., javax. and org.apache.camel. is applied. Use to accept any type.

String

Message Headers

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

Name Description Default Type

CamelJGroupsChannelAddress (common)

Constant: HEADER_JGROUPS_CHANNEL_ADDRESS

Address (org.jgroups.Address) of the channel associated with the endpoint.

Address

CamelJGroupsDest (common)

Constant: HEADER_JGROUPS_DEST

Consumer: The org.jgroups.Address instance extracted by org.jgroups.Message.getDest() method of the consumed message. Producer: The custom destination org.jgroups.Address of the message to be sent.

Address

CamelJGroupsSrc (common)

Constant: HEADER_JGROUPS_SRC

Consumer : The org.jgroups.Address instance extracted by org.jgroups.Message.getSrc() method of the consumed message. Producer: The custom source org.jgroups.Address of the message to be sent.

Address

CamelJGroupsOriginalMessage (common)

Constant: HEADER_JGROUPS_ORIGINAL_MESSAGE

The original org.jgroups.Message instance from which the body of the consumed message has been extracted.

Message

Security

The jgroups consumer converts an incoming cluster message into the exchange body by calling org.jgroups.Message.getObject() , which Java-deserializes the payload carried by the message. Deserialization is performed by JGroups on its own receive path, and the bodies a consumer receives originate from any peer that has joined the cluster.

The default JGroups protocol stack ( udp.xml ) multicasts over UDP and does not authenticate or encrypt peers: any host able to reach the cluster’s multicast group or bind port can join and send messages. Treat cluster peers as part of your trust boundary and harden the deployment accordingly.

  • Authenticate and encrypt the channel. Supply a hardened JGroups configuration through the channelProperties option and add the AUTH protocol together with SYM_ENCRYPT or ASYM_ENCRYPT , so that only trusted peers can join and message contents are protected on the wire. See the JGroups documentation for the protocol-stack reference.

  • Constrain deserialization at the JVM. Set a JVM-wide JEP-290 serialization filter ( -Djdk.serialFilter=…​ or ObjectInputFilter.Config.setSerialFilter(…​) ) to restrict which classes may be deserialized from the network. Because JGroups deserializes messages inside its own receive path, the JVM-wide filter is the mechanism that constrains that deserialization.

  • Restrict the accepted body types in Camel. The consumer applies a JEP-290 ObjectInputFilter pattern to the type of the message body before the exchange is routed, and refuses bodies whose type is not allowed. This is a defense-in-depth allow-list applied after JGroups has deserialized the message; it complements, but does not replace, the JVM-wide jdk.serialFilter and the channel authentication and encryption above.

The consumer deserialization filter

The class check is applied by default. When the deserializationFilter option is not configured, the JVM-wide jdk.serialFilter is honoured if it is set, otherwise the shared Camel default allow-list is applied: it permits standard Java and Apache Camel types, denies java.net.** , and rejects everything else.

A route that exchanges its own classes over the cluster must widen the filter through the deserializationFilter option, listing the packages it accepts: 

from("jgroups:clusterName?deserializationFilter=com.example.model.**;java.**;!*")
  .to("seda:queue");

The snippet below accepts only String bodies from the cluster, on top of a hardened, authenticated and encrypted channel supplied through channelProperties : 

from("jgroups:clusterName?channelProperties=secure-udp.xml&deserializationFilter=java.lang.String;!*")
  .to("seda:queue");

Setting deserializationFilter=* accepts any type and so opts out of the check.

A refused message is not routed. It is reported to the consumer’s ExceptionHandler , which logs it at WARN level by default, and is passed to the route error handler when bridgeErrorHandler=true is set.

Usage

Using jgroups component on the consumer side of the route will capture messages received by the JChannel associated with the endpoint and forward them to the Camel route. JGroups consumer processes incoming messages asynchronously .

  • Java

  • XML

  • YAML 

from("jgroups:clusterName").to("seda:queue");
<route>
  <from uri="jgroups:clusterName"/>
  <to uri="seda:queue"/>
</route>
- route:
    from:
      uri: jgroups:clusterName
      steps:
        - to:
            uri: seda:queue

Using jgroups component on the producer side of the route will forward body of the Camel exchanges to the JChannel instance managed by the endpoint.

  • Java

  • XML

  • YAML 

from("direct:start").to("jgroups:clusterName");
<route>
  <from uri="direct:start"/>
  <to uri="jgroups:clusterName"/>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - to:
            uri: jgroups:clusterName

Predefined filters

JGroups component comes with predefined filters factory class named JGroupsFilters.

If you would like to consume only view changes notifications sent to coordinator of the cluster (and ignore these sent to the "slave" nodes), use the JGroupsFilters.dropNonCoordinatorViews() filter. This filter is particularly useful when you want a single Camel node to become the master in the cluster, because messages passing this filter notifies you when a given node has become a coordinator of the cluster. The snippet below demonstrates how to collect only messages received by the master node.

Java-only: Java static import and filter EIP 
import static org.apache.camel.component.jgroups.JGroupsFilters.dropNonCoordinatorViews;
...
from("jgroups:clusterName?enableViewMessages=true").
  filter(dropNonCoordinatorViews()).
  to("seda:masterNodeEventsQueue");

Predefined expressions

JGroups component comes with predefined expressions factory class named JGroupsExpressions.

If you would like to create delayer that would affect the route only if the Camel context has not been started yet, use the JGroupsExpressions.delayIfContextNotStarted(long delay) factory method. The expression created by this factory method will return given delay value only if the Camel context is in the state different from started . This expression is particularly useful if you would like to use JGroups component for keeping singleton (master) route within the cluster. Control Bus start command won’t initialize the singleton route if the Camel Context hasn’t been yet started. So you need to delay a startup of the master route, to be sure that it has been initialized after the Camel Context startup. Because such a scenario can happen only during the initialization of the cluster, we don’t want to delay startup of the slave node becoming the new master - that’s why we need a conditional delay expression.

The snippet below demonstrates how to use conditional delaying with the JGroups component to delay the initial startup of master node in the cluster.

Java-only: Java static imports with conditional delay expression 
import static java.util.concurrent.TimeUnit.SECONDS;
import static org.apache.camel.component.jgroups.JGroupsExpressions.delayIfContextNotStarted;
import static org.apache.camel.component.jgroups.JGroupsFilters.dropNonCoordinatorViews;
...
from("jgroups:clusterName?enableViewMessages=true").
  filter(dropNonCoordinatorViews()).
  threads().delay(delayIfContextNotStarted(SECONDS.toMillis(5))). // run in separated and delayed thread. Delay only if the context hasn't been started already.
  to("controlbus:route?routeId=masterRoute&action=start&async=true");

from("timer://master?repeatCount=1").routeId("masterRoute").autoStartup(false).to(masterMockUri);

Examples

Sending (receiving) messages to (from) the JGroups cluster

To send a message to the JGroups cluster, use producer endpoint, just as demonstrated in the snippet below.

Java-only: Java test API (ProducerTemplate) 
from("direct:start").to("jgroups:myCluster");
...
producerTemplate.sendBody("direct:start", "msg")

To receive the message from the snippet above (on the same, or the other physical machine), listen to the messages coming from the given cluster, just as demonstrated on the code fragment below.

Java-only: Java test API (MockEndpoint assertions) 
mockEndpoint.setExpectedMessageCount(1);
mockEndpoint.message(0).body().isEqualTo("msg");
...
from("jgroups:myCluster").to("mock:messagesFromTheCluster");
...
mockEndpoint.assertIsSatisfied();

Receive cluster view change notifications

The snippet below demonstrates how to create the consumer endpoint listening to the notifications regarding cluster membership changes. By default, the endpoint consumes only regular messages.

Java-only: Java test API (MockEndpoint assertions) 
mockEndpoint.setExpectedMessageCount(1);
mockEndpoint.message(0).body().isInstanceOf(org.jgroups.View.class);
...
from("jgroups:clusterName?enableViewMessages=true").to(mockEndpoint);
...
mockEndpoint.assertIsSatisfied();