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Multiple Containers Using Docker Compose

Docker Compose is a tool for defining and running complex applications with Docker. With Compose, you define a multi-container application in a single file, then spin your application up in a single command which does everything that needs to be done to get it running.
— github.com/docker/compose

An application using Docker containers will typically consist of multiple containers. With Docker Compose, there is no need to write shell scripts to start your containers. All the containers are defined in a configuration file using services, and then docker-compose script is used to start, stop, and restart the application and all the services in that application, and all the containers within that service. The complete list of commands is:

Command Purpose

build

Build or rebuild services

help

Get help on a command

kill

Kill containers

logs

View output from containers

port

Print the public port for a port binding

ps

List containers

pull

Pulls service images

restart

Restart services

rm

Remove stopped containers

run

Run a one-off command

scale

Set number of containers for a service

start

Start services

stop

Stop services

up

Create and start containers

Docker Compose applications can use “classic” container linking that is confined to a single host. Alternatively, it can use multi-host networking introduced in Docker 1.9.

Single Host Container Linking

Configuration File

  1. Entry point to Compose is docker-compose.yml. Lets use the following file:

    mysqldb:
  image: mysql
  environment:
    MYSQL_DATABASE: sample
    MYSQL_USER: mysql
    MYSQL_PASSWORD: mysql
    MYSQL_ROOT_PASSWORD: supersecret
mywildfly:
  image: arungupta/wildfly-mysql-javaee7
  links:
    - mysqldb:db
  ports:
    - 8080:8080

    1. Two services defined by the name mysqldb and mywildfly

    2. Image name for each service defined using image

    3. Environment variables for the MySQL container are defined in environment

    4. MySQL container is linked with WildFly container using links

    5. Port forwarding is achieved using ports

Start Services

  1. All services can be started, in detached mode, by giving the command:

    docker-compose up -d

    And this shows the output as:

    Creating attendees_mysqldb_1...
Creating attendees_mywildfly_1...

    An alternate compose file name can be specified using -f.

    An alternate directory where the compose file exists can be specified using -p.

  2. Started services can be verified as:

    > docker-compose ps
        Name                       Command               State                Ports
-------------------------------------------------------------------------------------------------
attendees_mysqldb_1     /entrypoint.sh mysqld            Up      3306/tcp
attendees_mywildfly_1   /opt/jboss/wildfly/customi ...   Up      0.0.0.0:8080->8080/tcp, 9990/tcp

    This provides a consolidated view of all the services started, and containers within them.

    Alternatively, the containers in this application, and any additional containers running on this Docker host can be verified by using the usual docker ps command:

    > docker ps
CONTAINER ID        IMAGE                                    COMMAND                CREATED             STATUS              PORTS                              NAMES
3598e545bd2f        arungupta/wildfly-mysql-javaee7:latest   "/opt/jboss/wildfly/   59 seconds ago      Up 58 seconds       0.0.0.0:8080->8080/tcp, 9990/tcp   attendees_mywildfly_1
b8cf6a3d518b        mysql:latest                             "/entrypoint.sh mysq   2 minutes ago       Up 2 minutes        3306/tcp                           attendees_mysqldb_1

  3. Service logs can be seen as:

    > docker-compose logs
Attaching to attendees_mywildfly_1, attendees_mysqldb_1
mywildfly_1 | => Starting WildFly server
mywildfly_1 | => Waiting for the server to boot
mywildfly_1 | =========================================================================
mywildfly_1 |
mywildfly_1 |   JBoss Bootstrap Environment
mywildfly_1 |
mywildfly_1 |   JBOSS_HOME: /opt/jboss/wildfly
mywildfly_1 |
mywildfly_1 |   JAVA: /usr/lib/jvm/java/bin/java
mywildfly_1 |
mywildfly_1 |   JAVA_OPTS:  -server -Xms64m -Xmx512m -XX:MaxPermSize=256m -Djava.net.preferIPv4Stack=true -Djboss.modules.system.pkgs=org.jboss.byteman -Djava.awt.headless=true
mywildfly_1 |

. . .

mywildfly_1 | 15:40:20,866 INFO  [org.jboss.resteasy.spi.ResteasyDeployment] (MSC service thread 1-2) Deploying javax.ws.rs.core.Application: class org.javaee7.samples.employees.MyApplication
mywildfly_1 | 15:40:20,914 INFO  [org.wildfly.extension.undertow] (MSC service thread 1-2) JBAS017534: Registered web context: /employees
mywildfly_1 | 15:40:21,032 INFO  [org.jboss.as.server] (ServerService Thread Pool -- 28) JBAS018559: Deployed "employees.war" (runtime-name : "employees.war")
mywildfly_1 | 15:40:21,077 INFO  [org.jboss.as] (Controller Boot Thread) JBAS015961: Http management interface listening on http://127.0.0.1:9990/management
mywildfly_1 | 15:40:21,077 INFO  [org.jboss.as] (Controller Boot Thread) JBAS015951: Admin console listening on http://127.0.0.1:9990
mywildfly_1 | 15:40:21,077 INFO  [org.jboss.as] (Controller Boot Thread) JBAS015874: WildFly 8.2.0.Final "Tweek" started in 9572ms - Started 280 of 334 services (92 services are lazy, passive or on-demand)
mysqldb_1   | Running mysql_install_db
mysqldb_1   | 2015-06-05 15:38:31 0 [Note] /usr/sbin/mysqld (mysqld 5.6.25) starting as process 27 ...
mysqldb_1   | 2015-06-05 15:38:31 27 [Note] InnoDB: Using atomics to ref count buffer pool pages

. . .

mysqldb_1   | 2015-06-05 15:38:40 1 [Note] Event Scheduler: Loaded 0 events
mysqldb_1   | 2015-06-05 15:38:40 1 [Note] mysqld: ready for connections.
mysqldb_1   | Version: '5.6.25'  socket: '/var/run/mysqld/mysqld.sock'  port: 3306  MySQL Community Server (GPL)
mysqldb_1   | 2015-06-05 15:40:18 1 [Warning] IP address '172.17.0.24' could not be resolved: Name or service not known

Verify Application

  1. Access the application at http://dockerhost:8080/employees/resources/employees/. This is shown in the browser as:

docker compose output
Figure 1. Output From Servers Run Using Docker Compose

Stop Services

Stop the services as:

docker-compose stop
Stopping attendees_mywildfly_1...
Stopping attendees_mysqldb_1...
Warning

Stopping and starting the containers again will give the following error:

wildfly_1 |
wildfly_1 | 09:11:07,802 ERROR [org.jboss.as.controller.management-operation] (management-handler-thread - 4) JBAS014613: Operation ("add") failed - address: ([
wildfly_1 |     ("subsystem" => "datasources"),
wildfly_1 |     ("jdbc-driver" => "mysql")
wildfly_1 | ]) - failure description: "JBAS014803: Duplicate resource [
wildfly_1 |     (\"subsystem\" => \"datasources\"),
wildfly_1 |     (\"jdbc-driver\" => \"mysql\")
wildfly_1 | ]"

This is expected because the JDBC resource is created during every run of the container. In a real-world application, this would be pre-baked in the configuration already.

Remove Containers

Stop the services as:

docker-compose rm -f
Going to remove attendees_mywildfly_1, attendees_mysqldb_1
Removing attendees_mywildfly_1... done
Removing attendees_mysqldb_1... done

Scale Services

Multi-host Networking

Start a Java EE application with WildFly and MySQL containers.

  1. Create a new directory and name it wildfly-mysql-javaee7.

  2. Create a new file docker-compose.yml and copy the contents from the following:

    mysqldb:
  container_name: "db"
  image: mysql:latest
  environment:
    MYSQL_DATABASE: sample
    MYSQL_USER: mysql
    MYSQL_PASSWORD: mysql
    MYSQL_ROOT_PASSWORD: supersecret
mywildfly:
  image: arungupta/wildfly-mysql-javaee7
  environment:
    - MYSQL_URI=db:3306
  ports:
    - 8080:8080

  3. Run the application as:

    docker-compose --x-networking up -d

    --x-networking will create a bridge network. Docker 1.9 is required to run this application.