Configuring routes startup ordering and autostartup

Since Camel 2.1

Camel now supports configuring two aspects:

auto startup
order of starting routes

Configuring whether Camel should be auto started or not in XML DSL

The old option shouldStartContext have been removed and replaced with this new autoStartup option instead. What it allows is to configure Camel to not auto start when Spring starts.

For example the route below we have configured autoStartup=false to prevent Camel starting when Spring starts.

    <camelContext id="myCamel" xmlns="http://camel.apache.org/schema/spring" autoStartup="false">
        <route>
            <from uri="direct:start"/>
            <to uri="mock:result"/>
        </route>
    </camelContext>

So how do you start Camel then?

The autoStartup option on the <camelContext> is only used once, so you can manually start Camel later by invoking its start method as shown below:

    ApplicationContext ac = ...
    SpringCamelContext camel = (SpringCamelContext) ac.getBean("myCamel");

    // now start Camel manually
    camel.start();

Configuring whether a route should be started or not in XML DSL

You can use the autoStartup option to configure if a given route should be started when Camel starts. By default a route is auto started.

You can disable or enable it as follows.

In XML DSL you define it as follows:

<route autoStartup="false">
   <from uri="activemq:queue:special"/>
   <to uri="file://backup"/>
</route>

And to explicit state it should be started:

<route autoStartup="true">
   <from uri="activemq:queue:special"/>
   <to uri="file://backup"/>
</route>

Configuring whether a route should be started or not in Java DSL

You can use the autoStartup option to configure if a given route should be started when Camel starts. By default a route is auto started.

You can disable or enable it as follows:

from("activemq:queue:special").noAutoStartup().to("file://backup");

Configuring whether a route should be started or not, using a boolean or String, in Java DSL

Since Camel 2.9

To startup based on a boolean, String or Property, do one of the following:

boolean startupRoute = true;
from("activemq:queue:special").autoStartup(startupRoute).to("file://backup");
...
String startupRoute = "true";
from("activemq:queue:special").autoStartup(startupRoute).to("file://backup");
...
from("activemq:queue:special").autoStartup("{{startupRouteProperty}}").to("file://backup");

Configuring starting order for routes

You can also configure the order in which routes are started. Previously Camel started the routes in a non deterministic order. Now you have fine grained control in which order the routes should be started. There is a new attribute startupOrder which is an Integer that states the order. Camel then sorts the routes before starting time. The routes with the lowest startupOrder are started first and the ones with the highest are started last.

All startupOrder defined must be unique among all routes in your CamelContext. Otherwise if there are clashes in startupOrder numbers among routes, the routes will fail to start up throwing org.apache.camel.FailedToStartRouteException.

Normally you should also use numbers that are lower than 1000, as routes without an explicit startupOrder definition will have a number starting from 1000 auto assigned. So view numbers from 1000 upwards as reserved internally for Camel itself.

However, you can also utilise much higher numbers than 1000 (to avoid collisions with those auto assigned numbers) to specify the last routes to start up. Normally the usage of numbers starting from 10000 should be safe for the purpose.

In terms of the startupOrder there are no strict rules that it must start from 1 and increment by 1. You can for example use: 100, 200, 205, 89 if you like. Only rule of thumb is that the numbers must be unique.

Why do you want to control the starting order?

It can help in cases where routes are inter dependent on each other and also help with graceful shutting down Camel as Camel can stop the routes in the correct order as well.

Stopping routes

Camel 2.2: Camel will stop the routes in the same order that they were started.

Camel 2.3: Camel will stop the routes in the reverse order that they were started.

Examples

Let’s try a couple of examples.

Simple example

    from("seda:foo").startupOrder(1).to("mock:result");
    from("direct:start").startupOrder(2).to("seda:foo");

And the same example with XML DSL:

    <route startupOrder="1">
        <from uri="seda:foo"/>
        <to uri="mock:result"/>
    </route>

    <route startupOrder="2">
        <from uri="direct:start"/>
        <to uri="seda:foo"/>
    </route>

In this example we have two routes in which we have started that the direct:start route should be started after the seda:foo route. As direct:start is consider the input and we want that seda:foo route to be up and running beforehand.

You can also mix and match routes with and without startupOrder define.

Routes with startupOrder mixed with routes without

    from("seda:foo").startupOrder(1).to("mock:result");
    from("direct:start").startupOrder(2).to("seda:foo");

    from("direct:bar").to("seda:bar");

And the same example with XML DSL:

    <route startupOrder="1">
        <from uri="seda:foo"/>
        <to uri="mock:result"/>
    </route>

    <route startupOrder="2">
        <from uri="direct:start"/>
        <to uri="seda:foo"/>
    </route>

    <route>
        <from uri="direct:bar"/>
        <to uri="seda:bar"/>
    </route>

In the route above we have not define a startupOrder on the last route direct:bar in which Camel will auto assign a number for it, in which this case will be 1000. So therefore the route will be started last.

So you can use this to your advantage to only assign a startupOrder on the routes which really needs it.

Routes to start up last

    // use auto assigned startup ordering
    from("direct:start").to("seda:foo");

    // should start first
    from("seda:foo").startupOrder(1).to("mock:result");

    // should start last after the default routes
    from("direct:bar").startupOrder(12345).to("seda:bar");

    // use auto assigned startup ordering
    from("seda:bar").to("mock:other");

In the example above the order of startups of routes should be:

seda://foo
direct://start
seda://bar
direct://bar

Shutdown

Camel 2.2: Camel will shutdown the routes in the same order that they were started.

Camel 2.3: Camel will shutdown the routes in the reverse order that they were started.