Running Web Application in Linked Docker Containers Environment

Arpit AggarwalDecember 18th, 2015Last Updated: December 17th, 2015

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In post Dockerizing Web Application with Puppet we hosted web application in a single container, this time we will host a web application in a linked docker container environment – one in which our database (mysql) resides leveraged by our web application hosted in another docker container.

Before start, let’s have a brief about Linking Docker containers and how it helps us.

Linking or connecting Docker containers?

Linking Docker containers allows containers to discover each other and securely transfer information between them. Linking set up a conduit between containers allowing recipient container securely access source container preventing exposing the source container to the network.

In this post, recipient container is the spring-application-container which we created in this post and source container is the database container which we create now.

Let’s start with creating database container and linking it with spring-application-container, following below steps:

Step 1: Create directory with any name for me it’s database-container inside directory docker (created in this post), as follows:

$ cd docker
$ mkdir database-container
$ cd database-container
$ touch Dockerfile

Step 2: Copy the below content in docker/database-container/Dockerfile:

FROM ubuntu:latest
MAINTAINER arpitaggarwal "aggarwalarpit.89@gmail.com"
RUN apt-get install -q -y mysql-server
RUN apt-get install -q -y mysql-client
RUN sed -i -e"s/^bind-address\s*=\s*127.0.0.1/bind-address = 0.0.0.0/" /etc/mysql/my.cnf
EXPOSE 3306

RUN sed -i -e”s/^bind-address\s*=\s*127.0.0.1/bind-address = 0.0.0.0/” /etc/mysql/my.cnf specified above is to set the MYSQL bind-address to 0.0.0.0 because it usually only listens on 127.0.0.1 by default.

Step 3: Build the newly created database-container as follows:

$ cd database-container
$ docker build --no-cache=true -t database .

database specified above refers to name of a database-container image.

Step 4: Start database-container assigning a name “db” and MYSQL Server installed as a service inside database-container, as follows:

$ docker run -P -it --name db database /bin/bash

Step 5: Modify the existing spring-application-container Dockerfile to copy the new application to the container which is using database hosted on database-container, as follows:

FROM ubuntu:latest
MAINTAINER arpitaggarwal "aggarwalarpit.89@gmail.com"
RUN apt-get -y update
RUN apt-get -q -y install git
RUN sudo apt-get install -y ruby
RUN apt-get install -y ruby-dev
RUN apt-get -y update
RUN apt-get install -y make
RUN apt-get install -y build-essential
RUN apt-get install -y puppet
RUN gem install librarian-puppet
ADD Puppetfile /
RUN librarian-puppet install
RUN puppet apply --modulepath=/modules -e "include java8 class { 'tomcat':version => '7',java_home => '/usr/lib/jvm/java-8-oracle'}"
RUN apt-get remove -y make puppet build-essential ruby-dev
COPY /spring-mysql/target/spring-mysql.war /var/lib/tomcat7/webapps/
EXPOSE 8080

Step 6: Build the the application inside a docker directory, this time spring-mysql cloned from github:

$ cd docker
$ git clone https://github.com/arpitaggarwal/spring-mysql.git
$ cd spring-mysql
$ mvn clean install

Step 7: Next, start spring-application-container linking it with database-container as follows:

$ docker run -p 8080:8080 -it --name webapp --link db spring-application-container /bin/bash

–link flag specified above create a secure link between spring-application-container with the database-container and exposes connectivity information for the source container to the recipient container in two ways:

a) Environment variables.
b) Updating the /etc/hosts file.

Now we can use exposed environment variables or the entries from host to access the db container. Also, If we restart the source container, the linked containers /etc/hosts files will be automatically updated with the source container’s new IP address, allowing linked communication to continue.

In our application, we used the host entry mechanism to read the IP address of source container, using Java InetAddress.

Step 8: Our application will try to access the mysql database with user as “test” and password as “test” and use the employee table to store the employee details submitted from application, so let’s create it:

$ mysql --user=root mysql
$ CREATE USER 'test'@'%' IDENTIFIED BY 'test’;
$ GRANT ALL PRIVILEGES ON *.* TO 'test'@'%' WITH GRANT OPTION;
$ FLUSH PRIVILEGES;
$ CREATE DATABASE  test;
$ USE TEST;
$ CREATE TABLE employee (id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, name VARCHAR(20), age VARCHAR(30));

Step 9: Get your Docker container IP Address, using docker-machine:

docker-machine ip your_vm_name

Next, create employee submitting name and age from application and refresh the screen to retrieve it from database at url http://container-ip-address:8080/spring-mysql