Let me share some thoughts on how one can use Docker and Fig to run custom webapps in Tomcat and Postgres.

Tools that we are using

  • Docker - Gives ability to run any App in a container
  • Fig - helps run a combined setup of few Docker containers
  • boot2docker - sets up special Virtual Machine and gives ability to run Docker on Mac OS X
  • Tomcat - Java app server
  • PostgreSQL - SQL Database

What do we want

We want: - run a custom set of Java webapps - custom Tomcat configuration - simulate development environment - Webapps are pre-configured to talk with DB on localhost - in Docker

Installing tools

Configuring

We will use a custom Tomcat docker, that will pre-install postgresql-client and socat. The socat is used for forwarding a local port 5432 to the remote address. Her’s our Dockerfile:

FROM tomcat:7
RUN apt-get update && apt-get install -y curl postgresql-client socat

Next, create the fig.yml:

web:
  build: .
  volumes:
   - tomcat:/usr/local/tomcat
   - startTomcatAll.sh:/start.sh
  command: "sh /start.sh"
  links:
   - db
  ports:
   - "8080:8080"
db:
  image: "postgres:9.4"
  ports:
   - "5432:5432"
  volumes:
   - postgres:/data

Some info: - build tells Fig to build a custom Docker container, and specifies where the Dockerfile is - volumes FROM:TO maps folder from the host OS, into the guest container. In our case, we have a tomcat folder which contains the config and the webapps, and a custom start script. - command executes the custom script upon start. NOTE: The last command should output something, or Fig will stop the container. tail -f catalina.out will do the job. - links tells what other containers shoul be linked. You will also get the environment variables like DB_PORT_5432_TCP, which we will use in our script. - ports tells what ports to map from container into host OS. - image tells what public image from Docker Hub to use.

The start.sh script will look like this:

#!/bin/sh

# Port forwarding: localhost:5432 -> $DB_PORT_5432_TCP:5432
env | grep DB_PORT_5432_TCP= | sed 's/.*_PORT_\([0-9]*\)_TCP=tcp:\/\/\(.*\):\(.*\)/socat TCP4-LISTEN:\1,fork,reuseaddr TCP4:\2:\3 \&/' | sh

# Check the DB connection by listing tables
psql -h localhost -U postgres -l

# Some scripts rely on the operating system...
echo "Ubuntu" > /etc/issue

# Start the custom Tomcat
startTomcat.sh

# Output the log, so Fig can catch this
tail -f /usr/local/tomcat/bin/catalina.out

A side note about Postgres container

A PostgreSQL official Docker container is set to be run from a user postgres. In Mac OS X the volumes are mounted with a current Mac user.

If we will mount a volume that contains the binary database files, when a container starts, Postgres will crash, because the username that is used to run a postgres does not match the username that the database files are.

The possible way to overcome is to tar the files and “untar” them on start of a container.

The other way is to import the SQL dump - psql -f /data/all_dbs.sql -h localhost -U postgre.

If you are on the Mac, you might want to tell boot2docker VM to forward the 5432 port to your Mac. to do so, run

VBoxManage modifyvm "boot2docker-vm" --natpf1 "tcp-port5432,tcp,,5432,,5432";

Starting up

If you’r on a Mac, make sure the boot2docker VM is started - boot2docker start. Next, make sure that the environment is properly set by running $(boot2docker shellinit).

Run fig up and watch the Fig will start the db and web containers and outputs the log into the console. You could run docker build . to build your Dockerfile, but fig will do it for you.

Now you can open your browser on localhost:8080 and see your Tomcat app.

You can connect to any container from other shell by running docker exec -i -t test_web_1 bash (or _db_1)

Cleanup

  • docker images will list all images (-a will list all)
  • docker ps will list running containers (-a for all)
  • fig rm will remove all stopped containers
  • docker images -f dangling=true -q |xargs docker rmi -f - will remove all dangling (not-named) Docker images