2.10. Controlling Start-Up and Shutdown of Routes
Overview
By default, routes are automatically started when your Apache Camel application (as represented by the
CamelContext instance) starts up and routes are automatically shut down when your Apache Camel application shuts down. For non-critical deployments, the details of the shutdown sequence are usually not very important. But in a production environment, it is often crucial that existing tasks should run to completion during shutdown, in order to avoid data loss. You typically also want to control the order in which routes shut down, so that dependencies are not violated (which would prevent existing tasks from running to completion).
For this reason, Apache Camel provides a set of features to support graceful shutdown of applications. Graceful shutdown gives you full control over the stopping and starting of routes, enabling you to control the shutdown order of routes and enabling current tasks to run to completion.
Setting the route ID
It is good practice to assign a route ID to each of your routes. As well as making logging messages and management features more informative, the use of route IDs enables you to apply greater control over the stopping and starting of routes.
For example, in the Java DSL, you can assign the route ID,
myCustomerRouteId, to a route by invoking the routeId() command as follows:
from("SourceURI").routeId("myCustomRouteId").process(...).to(TargetURI);
In the XML DSL, set the
route element's id attribute, as follows:
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring">
<route id="myCustomRouteId" >
<from uri="SourceURI"/>
<process ref="someProcessorId"/>
<to uri="TargetURI"/>
</route>
</camelContext>Disabling automatic start-up of routes
By default, all of the routes that the CamelContext knows about at start time will be started automatically. If you want to control the start-up of a particular route manually, however, you might prefer to disable automatic start-up for that route.
To control whether a Java DSL route starts up automatically, invoke the
autoStartup command, either with a boolean argument (true or false) or a String argument (true or false). For example, you can disable automatic start-up of a route in the Java DSL, as follows:
from("SourceURI")
.routeId("nonAuto")
.autoStartup(false)
.to(TargetURI);
You can disable automatic start-up of a route in the XML DSL by setting the
autoStartup attribute to false on the route element, as follows:
<camelContext id="CamelContextID" xmlns="http://camel.apache.org/schema/spring">
<route id="nonAuto" autoStartup="false">
<from uri="SourceURI"/>
<to uri="TargetURI"/>
</route>
</camelContext>Manually starting and stopping routes
You can manually start or stop a route at any time in Java by invoking the
startRoute() and stopRoute() methods on the CamelContext instance. For example, to start the route having the route ID, nonAuto, invoke the startRoute() method on the CamelContext instance, context, as follows:
// Java
context.startRoute("nonAuto");
To stop the route having the route ID,
nonAuto, invoke the stopRoute() method on the CamelContext instance, context, as follows:
// Java
context.stopRoute("nonAuto");Startup order of routes
By default, Apache Camel starts up routes in a non-deterministic order. In some applications, however, it can be important to control the startup order. To control the startup order in the Java DSL, use the
startupOrder() command, which takes a positive integer value as its argument. The route with the lowest integer value starts first, followed by the routes with successively higher startup order values.
For example, the first two routes in the following example are linked together through the
seda:buffer endpoint. You can ensure that the first route segment starts after the second route segment by assigning startup orders (2 and 1 respectively), as follows:
Example 2.5. Startup Order in Java DSL
from("jetty:http://fooserver:8080")
.routeId("first")
.startupOrder(2)
.to("seda:buffer");
from("seda:buffer")
.routeId("second")
.startupOrder(1)
.to("mock:result");
// This route's startup order is unspecified
from("jms:queue:foo").to("jms:queue:bar");
Or in Spring XML, you can achieve the same effect by setting the
route element's startupOrder attribute, as follows:
Example 2.6. Startup Order in XML DSL
<route id="first" startupOrder="2">
<from uri="jetty:http://fooserver:8080"/>
<to uri="seda:buffer"/>
</route>
<route id="second" startupOrder="1">
<from uri="seda:buffer"/>
<to uri="mock:result"/>
</route>
<!-- This route's startup order is unspecified -->
<route>
<from uri="jms:queue:foo"/>
<to uri="jms:queue:bar"/>
</route>
Each route must be assigned a unique startup order value. You can choose any positive integer value that is less than 1000. Values of 1000 and over are reserved for Apache Camel, which automatically assigns these values to routes without an explicit startup value. For example, the last route in the preceding example would automatically be assigned the startup value, 1000 (so it starts up after the first two routes).
Shutdown sequence
When a
CamelContext instance is shutting down, Apache Camel controls the shutdown sequence using a pluggable shutdown strategy. The default shutdown strategy implements the following shutdown sequence:
- Routes are shut down in the reverse of the start-up order.
- Normally, the shutdown strategy waits until the currently active exchanges have finshed processing. The treatment of running tasks is configurable, however.
- Overall, the shutdown sequence is bound by a timeout (default, 300 seconds). If the shutdown sequence exceeds this timeout, the shutdown strategy will force shutdown to occur, even if some tasks are still running.
Shutdown order of routes
Routes are shut down in the reverse of the start-up order. That is, when a start-up order is defined using the
startupOrder() command (in Java DSL) or startupOrder attribute (in XML DSL), the first route to shut down is the route with the highest integer value assigned by the start-up order and the last route to shut down is the route with the lowest integer value assigned by the start-up order.
For example, in Example 2.5, “Startup Order in Java DSL”, the first route segment to be shut down is the route with the ID,
first, and the second route segment to be shut down is the route with the ID, second. This example illustrates a general rule, which you should observe when shutting down routes: the routes that expose externally-accessible consumer endpoints should be shut down first, because this helps to throttle the flow of messages through the rest of the route graph.
Note
Apache Camel also provides the option
shutdownRoute(Defer), which enables you to specify that a route must be amongst the last routes to shut down (overriding the start-up order value). But you should rarely ever need this option. This option was mainly needed as a workaround for earlier versions of Apache Camel (prior to 2.3), for which routes would shut down in the same order as the start-up order.
Shutting down running tasks in a route
If a route is still processing messages when the shutdown starts, the shutdown strategy normally waits until the currently active exchange has finished processing before shutting down the route. This behavior can be configured on each route using the
shutdownRunningTask option, which can take either of the following values:
-
ShutdownRunningTask.CompleteCurrentTaskOnly - (Default) Usually, a route operates on just a single message at a time, so you can safely shut down the route after the current task has completed.
-
ShutdownRunningTask.CompleteAllTasks - Specify this option in order to shut down batch consumers gracefully. Some consumer endpoints (for example, File, FTP, Mail, iBATIS, and JPA) operate on a batch of messages at a time. For these endpoints, it is more appropriate to wait until all of the messages in the current batch have completed.
For example, to shut down a File consumer endpoint gracefully, you should specify the
CompleteAllTasks option, as shown in the following Java DSL fragment:
// Java
public void configure() throws Exception {
from("file:target/pending")
.routeId("first").startupOrder(2)
.shutdownRunningTask(ShutdownRunningTask.CompleteAllTasks)
.delay(1000).to("seda:foo");
from("seda:foo")
.routeId("second").startupOrder(1)
.to("mock:bar");
}
The same route can be defined in the XML DSL as follows:
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
<!-- let this route complete all its pending messages when asked to shut down -->
<route id="first"
startupOrder="2"
shutdownRunningTask="CompleteAllTasks">
<from uri="file:target/pending"/>
<delay><constant>1000</constant></delay>
<to uri="seda:foo"/>
</route>
<route id="second" startupOrder="1">
<from uri="seda:foo"/>
<to uri="mock:bar"/>
</route>
</camelContext>Shutdown timeout
The shutdown timeout has a default value of 300 seconds. You can change the value of the timeout by invoking the
setTimeout() method on the shutdown strategy. For example, you can change the timeout value to 600 seconds, as follows:
// Java // context = CamelContext instance context.getShutdownStrategy().setTimeout(600);
Integration with custom components
If you are implementing a custom Apache Camel component (which also inherits from the
org.apache.camel.Service interface), you can ensure that your custom code receives a shutdown notification by implementing the org.apache.camel.spi.ShutdownPrepared interface. This gives the component an opportunity execute custom code in preparation for shutdown.
