Question

I’m trying to start a Camel route on GAE and am running into one brick wall after the next. First I tried a route that looked like this:

from("direct:start")
    .process(new Processor() {
        @Override
        public void process(Exchange exchange) {
            logger.info("I made it!");
        }
    })
    .to("direct:end");

But that doesn’t do anything. Being new to both Camel and GAE, I suspect that’s because the direct component doesn’t act as a consumer for the beginning of a route. So then I tried kicking off a timer:

from("timer://runOnce?repeatCount=1")
    .process(new Processor() {
        @Override
        public void process(Exchange exchange) {
            logger.info("I made it!");
        }
    })
    .to("direct:end");

Only to get a nasty error from GAE:

Error: access denied (java.lang.RuntimePermission modifyThreadGroup)

And it turns out you can’t create new Thread instances on GAE, and that’s exactly what the Timer component does.

So then I tried kicking the route off with a bean:

public class DummyBean {
    public void kickoffRoute() { return; }
}

// Inside the method that creates and starts the Camel route
SimpleRegistry reg = new SimpleRegistry();
DummyBean bean = new DummyBean();
reg.put("dummy", bean);

CamelContext camel = new DefaultCamelContext(reg);
camel.disableJMX();

// Inside my RouteBuilder
from("bean:dummy")
    .process(new Processor() {
        @Override
        public void process(Exchange exchange) {
            logger.info("I made it!");
        }
    })
    .to("direct:end");

I ran this, only to get the same “access denied” error as from before with the Timer.

All I’m trying to do is kick off a route from inside GAE so I can start getting familiar with both technologies (Camel & GAE). But for the life of me, I can’t figure out how to do this – every Camel component seems to create threads, which are illegal on GAE! So I ask:

1. How do you even kickoff a route (an initial producer – Timer, or otherwise) on GAE? I see there is a Camel-GAE component, and I’m certainly willing to read up on it and learn how to use it, so that I could have routes starting with, say, a ghttp:///startRoute endpoint, but I’m really just starting out here and am hoping for an easier component/endpoint to work with.
2. If both Timer and Bean components create threads, and this is disallowed on GAE, I have a sick feeling in my stomach that most/all Camel components are disallowed on GAE. Is this the case?!?! If so, how do you build useful/meaningful routes on GAE? Or is there some GAE “trick” to getting Camel to run and create threads? For instance, I know GAE backends do not suffer the same threading restrictions as frontend instances, etc.

Thanks in advance!

Answer 1

Camel is built to run on Java environments using Java SE 6/7 with whatever that implies in file system access, thread creation, possibilities to open ports etc.

Google App Engine has, as you realised, several restrictions. That does not make Camel unusable at all. You can use a lot of the routing features, producers endpoints (.to(..)), transformations, etc etc.

In fact, in Java EE Application Servers, there are similar restrictions, but that does not prevent usage of camel.

If you really are up for it, and need to do everything camel inside GAE, it’s perhaps possible to make jack in Camels pluggable threading models into GAE.

Disclaimer: I have never used GAE tasks, but there is some documentations here

https://developers.google.com/appengine/docs/java/taskqueue/
http://camel.apache.org/threading-model.html

You can also try to start the events by whatever feature you have in GAE and just use a producer template to kick start a Camel route.