Deploying Java EE Application to Docker Swarm Cluster

What is Docker Swarm?

Docker Swarm provides native clustering to Docker. Clustering using Docker Swarm 0.2.0 provide a basic introduction to Docker Swarm, and how to create a simple three node cluster. As a refresher, the key components of Docker Swarm are shown below:

In short, Swarm Manager is a pre-defined Docker Host, and is a single point for all administration. Additional Docker hosts are identified as Nodes and communicate with the Manager using TCP. By default, Swarm uses hosted Discovery Service, based on Docker Hub, using tokens to discover nodes that are part of a cluster. Each node runs a Node Agent that registers the referenced Docker daemon, monitors it, and updates the Discovery Service with the node’s status. The containers run on a node.

That blog provide complete details, but a quick summary to create the cluster is shown below:

# Create cluster
TOKEN=`docker run swarm create`
# Creating Swarm master
docker-machine create -d virtualbox --swarm --swarm-master --swarm-discovery token://$TOKEN swarm-master
# Creating swarm node 01
docker-machine create -d virtualbox --swarm --swarm-discovery token://$TOKEN swarm-node-01
Create swarm node 02
docker-machine create -d virtualbox --swarm --swarm-discovery token://$TOKEN swarm-node-02

Listing the cluster shows:

NAME            ACTIVE   DRIVER       STATE     URL                         SWARM
swarm-master             virtualbox   Running   tcp://   swarm-master (master)
swarm-node-01            virtualbox   Running   tcp://   swarm-master
swarm-node-02   *        virtualbox   Running   tcp://   swarm-master

It has one master and two nodes.

Deploy a Java EE application to Docker Swarm

All hosts in the cluster are accessible using a single, virtual host. Swarm serves the standard Docker API, so any tool that communicates with a single Docker host communicate can scale to multiple Docker hosts by communicating to this virtual host.

Docker Container Linking Across Multiple Hosts explains how to link containers across multiple Docker hosts. It deploys a Java EE 7 application to WildFly on one Docker host, and connects it with a MySQL container running on a different Docker host. We can deploy both of these containers using the virtual host, and they will then be deployed to the Docker Swarm cluster.

Lets get started!

MySQL on Docker Swarm

  1. Start the MySQL container
    docker run --name mysqldb -e MYSQL_USER=mysql -e MYSQL_PASSWORD=mysql -e MYSQL_DATABASE=sample -e MYSQL_ROOT_PASSWORD=supersecret -p 3306:3306 -d mysql
  2. Status of the container can be seen as:
    CONTAINER ID        IMAGE               COMMAND                CREATED             STATUS              PORTS                           NAMES
    b49d627a0431        mysql:latest        "/ mysq   5 minutes ago       Up 4 minutes>3306/tcp   swarm-node-01/mysqldb

    It shows the container is running on swarm-node-01.

    Make sure you are connected to the Docker Swarm cluster using eval $(docker-machine env --swarm swarm-master).

  3. Find IP address of the host where this container is started:
    ~> docker inspect --format '{{ .Node.Ip }}' $(docker ps -q --filter 'name=*mysqldb*')

    Note IP address of the node where MySQL server is running. This will be used when starting WildFly application server later.

    ps: Filtering by name seem to not return accurate results (#10897).

WildFly on Docker Swarm

  1. Start WildFly application server by passing the IP address of the host and the port on which MySQL server is running:
    ~> docker run --name mywildfly -e MYSQL_HOST= -e MYSQL_PORT=3306 -p 8080:8080 -d arungupta/wildfly-mysql-javaee7:host
  2. Status of the container can be seen as:
    ~> docker ps
    CONTAINER ID        IMAGE                                  COMMAND                CREATED             STATUS              PORTS                           NAMES
    ab5717083812        arungupta/wildfly-mysql-javaee7:host   "/opt/jboss/wildfly/   25 minutes ago      Up 25 minutes>8080/tcp   swarm-node-02/mywildfly   
    b49d627a0431        mysql:latest                           "/ mysq   34 minutes ago      Up 33 minutes>3306/tcp   swarm-node-01/mysqldb

    It shows the container is running on swarm-node-02. IP address of the host is also shown in the PORTS column.

    As explained in Tech Tip #69, JDBC URL of the data source uses the specified IP address and port for connecting with the MySQL server. However passing IP address is very brittle as the MySQL server may restart on a different Docker host. This is filed as #773.

  3. Access the application at:
    ~> curl
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?><collection><employee><id>1</id><name>Penny</name></employee><employee><id>2</id><name>Sheldon</name></employee><employee><id>3</id><name>Amy</name></employee><employee><id>4</id><name>Leonard</name></employee><employee><id>5</id><name>Bernadette</name></employee><employee><id>6</id><name>Raj</name></employee><employee><id>7</id><name>Howard</name></employee><employee><id>8</id><name>Priya</name></employee></collection>

    This is using the IP address of the host where the container is started.


Arun Gupta

Arun is a technology enthusiast, avid runner, author of a best-selling book, globe trotter, a community guy, Java Champion, JavaOne Rockstar, JUG Leader, Minecraft Modder, Devoxx4Kids-er, and a Red Hatter.
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