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Bilgin Ibryam is a software engineer with Master's degree in Computer Science and currently working for Red Hat in London. He is also the author of "Instant Apache Camel Message Routing" book, an open source enthusiast, Apache OFBiz, and Apache Camel committer. In his spare time, he enjoys contributing to open source projects and blogging at ofbizian.com. Bilgin is a DZone MVB and is not an employee of DZone and has posted 21 posts at DZone. You can read more from them at their website. View Full User Profile

A Camel Demo for Amazon's Simple Worklfow Service

01.13.2014
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In a previous post I explained why AWS SWF service is good and announced the new Camel SWF component. Now the component documentation is ready and here is a simple, fully working demo. It consist of three independent standalone Camel routes:

A workflow producer allows us to interact with a workflow. It can start a new workflow execution, query its state, send signals to a running workflow, or terminate and cancel it. In our demo, the WorkflowProducer starts a route that schedules 10 workflow executions where the each execution receives as an argument a number.

package com.ofbizian.swf.demo;

import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.main.Main;

public class WorkflowProducer {

    public static String COMMON_OPTIONS =
        "accessKey=XXX"
        + "&secretKey=XXX"
        + "&domainName=demo"
        + "&workflowList=demo-wlist"
        + "&activityList=demo-alist"
        + "&version=1.0"
        + "&clientConfiguration.endpoint=swf.eu-west-12.amazonaws.com";

    public static void main(String[] args) throws Exception {
        Main main = new Main();
        main.enableHangupSupport();
        WorkflowProducerRoute route = new WorkflowProducerRoute();
        main.addRouteBuilder(route);
        main.run();
    }

    static class WorkflowProducerRoute extends RouteBuilder {

        @Override
        public void configure() throws Exception {

            from("timer://workflowProducer?repeatCount=10")
                    .setBody(property("CamelTimerCounter"))
                    .to("aws-swf://workflow?" + COMMON_OPTIONS + "&eventName=calculator")
                    .log("SENT WORKFLOW TASK ${body}");
        }
    }
}

Once a workflow execution is scheduled, we need a process that will decide what are the next steps for it. In Camel it is done using a Workflow Consumer. A workflow consumer represents the workflow logic. When it is started, it will start polling workflow decision tasks and process them. In addition to processing decision tasks, a workflow consumer route, will also receive signals (send from a workflow producer) or state queries. The primary purpose of a workflow consumer is to schedule activity tasks for execution using activity producers. Actually activity tasks can be scheduled only from a thread started by a workflow consumer.

package com.ofbizian.swf.demo;

import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.component.aws.swf.SWFConstants;
import org.apache.camel.main.Main;

public class WorkflowConsumer {

    public static void main(String[] args) throws Exception {
        Main main = new Main();
        main.enableHangupSupport();
        WorkflowConsumerRoute route = new WorkflowConsumerRoute();
        main.addRouteBuilder(route);
        main.run();
    }

    static class WorkflowConsumerRoute extends RouteBuilder {

        @Override
        public void configure() throws Exception {

            from("aws-swf://workflow?" + WorkflowProducer.COMMON_OPTIONS + "&eventName=calculator")

                    .choice()
                        .when(header(SWFConstants.ACTION).isEqualTo(SWFConstants.SIGNAL_RECEIVED_ACTION))
                            .log("Signal received ${body}")

                        .when(header(SWFConstants.ACTION).isEqualTo(SWFConstants.GET_STATE_ACTION))
                            .log("State asked ${body}")

                        .when(header(SWFConstants.ACTION).isEqualTo(SWFConstants.EXECUTE_ACTION))

                            .setBody(simple("${body[0]}"))
                            .log("EXECUTION TASK RECEIVED ${body}")

                            .filter(simple("${body} > 5"))
                                .to("aws-swf://activity?" + WorkflowProducer.COMMON_OPTIONS + "&eventName=incrementor");
        }
    }

}

The logic in our demo decider is simple: if the incoming argument is greater than 5, we schedule a task for execution. Otherwise the workflow will complete as there are no other tasks to be executed. Notice that it also has branches for handing signal and state query events.

The final peace of our distributed (since it consists of three independent applications) workflow application is the ActivityConsumer that actually performs some calculations. It has the simplest possible implementation: increments the given argument and returns it.

package com.ofbizian.swf.demo;

import org.apache.camel.builder.RouteBuilder;
import org.apache.camel.main.Main;

public class ActivityConsumer {

    public static void main(String[] args) throws Exception {
        Main main = new Main();
        main.enableHangupSupport();
        ActivityConsumerRoute route = new ActivityConsumerRoute();
        main.addRouteBuilder(route);
        main.run();
    }

    static class ActivityConsumerRoute extends RouteBuilder {

        @Override
        public void configure() throws Exception {
from("aws-swf://activity?" + WorkflowProducer.COMMON_OPTIONS + "&eventName=incrementor")
                    .setBody(simple("${body[0]}"))
                    .log("RECEIVED ACTIVITY TASK ${body}")
                    .setBody(simple("${body}++"));
        }
    }
}

All you need to do to run this demo is to create the appropriate workflow domain and add your key/secret to the route.

Published at DZone with permission of Bilgin Ibryam, author and DZone MVB. (source)

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