Configuring Routes Startup Ordering and Auto-startup

Camel supports configuring two aspects:

auto-startup
order of starting routes

Auto-startup

The autoStartup option allows is to configure Camel to not auto start routes when Camel starts.

The auto startup can be configured on two levels:

Camel context: Globally
Route: Individually per route

For example, the CamelContext below we have configured autoStartup=false to prevent Camel starting all the routes on startup.

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

So how do you start the routes?

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

For example, when using Spring, you can get hold of the CamelContext via the Spring ApplicationContext:

ApplicationContext ac = ...
CamelContext camel = ac.getBean("myCamel", CamelContext.class);

// now start all the routes
camel.getRouteController().startAllRoutes();

The routes can also be started via JMX (requires camel-management JAR to be on the classpath) by invoking the startAllRoutes operation on the CamelContext MBean.

Auto-startup per route level

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

In XML DSL, you disable auto startup 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>

And in Java DSL you can configure auto startup on CamelContext as follows:

camelContext.setAutoStartup(false);

And on route level you can disable it via noAutoStartup:

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

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

// using a boolean
from("activemq:queue:special").autoStartup(false)
    .to("file://backup");

// using a string
from("activemq:queue:special").autoStartup("false")
    .to("file://backup");

// using property placeholders
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 use 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. The 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.

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

Let’s try a couple of examples.

Startup ordering example

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

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

And the same example with XML DSL:

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

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

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. Because direct:start is considered the input, and we want seda:foo route to be up and running beforehand.

Using startOrder together with non startOrder

You can also mix and match routes with and without startupOrder defined. The first two routes below have start order defined, and the last route has not.

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:

<routes>
    <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>
</routes>

In the route above we have not defined 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. 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.

Configuring routes to start up last

You can use a high number in startupOrder to have a specific route startup last as shown below:

// 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 route startups should be:

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

Shutting down routes

Apache Camel will shut down the routes in the reverse order that they were started.

See more at Graceful Shutdown.