There is plenty of material on microservices, just google it! I gave a presentation on refactoring monolith to microservices at Devoxx Belgium a couple of years back and it has good reviews:

This blog will show how Docker simplifies creation and shutting down of a microservice. All code used in this blog is at github.com/arun-gupta/couchbase-javaee.

Microservice Definition using Compose

Docker 1.13 introduced a v3 of Docker Compose. The changes in the syntax are minimal but the key difference is addition of deploy attribute. This attribute allows to specify replicas, rolling update and restart policy for the container. Our microservice will start a WldFly application server with a Java EE application pre-deployed. This application will talk to a Couchbase database to CRUD application data. Here is the Compose definition:

In this Compose file:

  1. Two services in this Compose are defined by the name db and web attributes
  2. Image name for each service defined using image attribute
  3. The arungupta/couchbase:travel image starts Couchbase server, configures it using Couchbase REST API, and loads travel-sample bucket with ~32k JSON documents.
  4. The arungupta/couchbase-javaee:travel image starts WildFly and deploys application WAR file built from https://github.com/arun-gupta/couchbase-javaee. Clone that project if you want to build your own image.
  5. envrionment attribute defines environment variables accessible by the application deployed in WildFly. COUCHBASE_URI refers to the database service. This is used in the application code as shown at https://github.com/arun-gupta/couchbase-javaee/blob/master/src/main/java/org/couchbase/sample/javaee/Database.java.
  6. Port forwarding is achieved using ports attribute
  7. depends_on attribute in Compose definition file ensures the container start up order. But application-level start up needs to be ensured by the applications running inside container. In our case, WildFly starts up rather quickly but takes a few seconds for the database to start up. This means the Java EE application deployed in WildFly is not able to communicate with the database. This outlines a best practice when building micro services applications: you must code defensively and ensure in your application initialization that the micro services you depend on have started, without assuming startup order. This is shown in the database initialization code at https://github.com/arun-gupta/couchbase-javaee/blob/master/src/main/java/org/couchbase/sample/javaee/Database.java. It performs the following checks:

    1. Bucket exists
    2. Query service of Couchbase is up and running
    3. Sample bucket is fully loaded

This application can be started using docker-compose up -d command on a single host. Or a cluster of Docker engines in swarm-mode using docker stack deploy command.

Setup Docker Swarm-mode

Initialize Swarm mode using the following command:

This starts a Swarm Manager. By default, manager node are also worker but can be configured to be manager-only.
Find some information about this one-node cluster using the command docker info command:

This cluster has 1 node, and that is manager. Alternatively, a multi-host cluster can be easily setup using Docker for AWS.

Deploy Microservice

The microservice can be started as:

This shows the output:

WildFly and Couchbase services are started on this node. Each service has a single container. If the Swarm mode is enabled on multiple nodes then the containers will be distributed across multiple nodes.
A new overlay network is created. This allows multiple containers on different hosts to communicate with each other.

Verify that the WildFly and Couchbase services are running using docker service ls:

Logs for the service can be seen using docker service logs -f webapp_web:

Make sure to wait for the last log statement to show.

Access Microservice

Get 10 airlines from the microservice:

This shows the results as:

Docker for Java Developers workshop is a self-paced hands-on lab and allows you to get started with Docker easily. Get a single resource:

Create a new resource:

Update a resource:

Delete a resource:

Detailed output from each of these commands is at github.com/arun-gupta/couchbase-javaee.

Delete Microservice

The microservice can be removed using  the command docker stack rm webapp:

Want to get started with Couchbase? Look at Couchbase Starter Kits. Want to learn more about running Couchbase in containers?

Author

Posted by Arun Gupta, VP, Developer Advocacy, Couchbase

Arun Gupta is the vice president of developer advocacy at Couchbase. He has built and led developer communities for 10+ years at Sun, Oracle, and Red Hat. He has deep expertise in leading cross-functional teams to develop and execute strategy, planning and execution of content, marketing campaigns, and programs. Prior to that he led engineering teams at Sun and is a founding member of the Java EE team. Gupta has authored more than 2,000 blog posts on technology. He has extensive speaking experience in more than 40 countries on myriad topics and is a JavaOne Rock Star for three years in a row. Gupta also founded the Devoxx4Kids chapter in the US and continues to promote technology education among children. An author of several books on technology, an avid runner, a globe trotter, a Java Champion, a JUG leader, NetBeans Dream Team member, and a Docker Captain, he is easily accessible at @arungupta.

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