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
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 component supports 6 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
Channel to use. |
JChannel |
||
Specifies configuration properties of the JChannel used by the endpoint. |
String |
||
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 |
|
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 |
|
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 |
|
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 endpoint is configured using URI syntax:
jgroups:clusterName
with the following path and query parameters:
Query Parameters (6 parameters)
Name | Description | Default | Type |
---|---|---|---|
Specifies configuration properties of the JChannel used by the endpoint. |
String |
||
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 |
|
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 |
|
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 |
||
Sets the exchange pattern when the consumer creates an exchange. Enum values:
|
ExchangePattern |
||
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 component supports 4 message header(s), which is/are listed below:
Name | Description | Default | Type |
---|---|---|---|
JGROUPS_CHANNEL_ADDRESS (common) Constant: |
Address (org.jgroups.Address) of the channel associated with the endpoint. |
Address |
|
Constant: |
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 |
|
Constant: |
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 |
|
JGROUPS_ORIGINAL_MESSAGE (common) Constant: |
The original org.jgroups.Message instance from which the body of the consumed message has been extracted. |
Message |
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.
// Capture messages from cluster named
// 'clusterName' and send them to Camel route.
from("jgroups:clusterName").to("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.
// Send message to the cluster named 'clusterName'
from("direct:start").to("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 given node has become a coordinator of the cluster. The snippet
below demonstrates how to collect only messages received by the master
node.
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 than
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 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.
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
In order to send message to the JGroups cluster use producer endpoint, just as demonstrated on the snippet below.
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 on the messages coming from the given cluster, just as demonstrated on the code fragment below.
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 only regular messages are consumed by the endpoint.
mockEndpoint.setExpectedMessageCount(1);
mockEndpoint.message(0).body().isInstanceOf(org.jgroups.View.class);
...
from("jgroups:clusterName?enableViewMessages=true").to(mockEndpoint);
...
mockEndpoint.assertIsSatisfied();
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`.
JGroupsLockClusterService service = new JGroupsLockClusterService();
service.setId("uniqueNodeId");
...
context.addService(service);
from("master:mycluster:jetty:http://localhost:8080/orders").to("jms:orders");
Spring Boot Auto-Configuration
When using jgroups 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-starter</artifactId>
<version>x.x.x</version>
<!-- use the same version as your Camel core version -->
</dependency>
The component supports 11 options, which are listed below.
Name | Description | Default | Type |
---|---|---|---|
Sets if the jgroups lock cluster service should be enabled or not, default is false. |
false |
Boolean |
|
Cluster Service ID. |
String |
||
JGroups Cluster name. |
String |
||
JGrups configuration File name. |
String |
||
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 |
|
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 |
|
Channel to use. The option is a org.jgroups.JChannel type. |
JChannel |
||
Specifies configuration properties of the JChannel used by the endpoint. |
String |
||
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 |
|
Whether to enable auto configuration of the jgroups component. This is enabled by default. |
Boolean |
||
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 |