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Exercise 2 - Running with a Persistent Database

Goals

  • Decouple database service from the application
  • Run a MySQL database on Docker
  • Learn about Docker persistent volumes and networking

Acceptance Criteria

  • Application configuration modified to connect to MySQL database
  • Docker image is rebuilt and tagged as pet-app
  • MySQL running in Docker
  • User-defined network created in Docker
  • Application running in Docker and linked to MySQL container
  • Application can be accessed on http://localhost:8080
  • New owner is created, with at least 1 pet
  • Kill and restart application container
  • Owner created in previous step is still available

Step by Step Instructions

First of all we will create a data folder to use as the container persistent volume, and then start an image of the MySQL 5.7 container and pass a few environment variables to create a new database, user, and password:

$ mkdir data
$ docker run -d --name pet-db -v $PWD/data:/var/lib/mysql -e MYSQL_RANDOM_ROOT_PASSWORD=yes -e MYSQL_DATABASE=petclinic -e MYSQL_USER=petclinic-user -e MYSQL_PASSWORD=S3cr3t mysql:5.7

Note: If you are on Windows 10 Home with Docker Toolbox and get an error trying to initialize InnoDB, please try adding --innodb-use-native-aio=false argument at the end of the docker run command

Now we will create a user-defined network for the containers to be able to connect to each other, and attach the running MySQL container to the network:

$ docker network create pet-net
c8e9dd492b9f9d73216ab71bc73277c44e99b057814821c2f083dc48f27e5dd8
$ docker network connect pet-net pet-db

Now we can start our application container, but this time enabling the mysql Spring profile with an environment variable, and also adding the --network option to connect to the user-defined network:

$ docker run --name=pet-app-prod -d -p 8080:8080 -e "SPRING_PROFILES_ACTIVE=mysql" --network pet-net pet-app
ff776db53488ff18644bfd79e39f7101501dbfd4cc0216f041051a1155a8adaf

Then you should be able to access the application by going to http://localhost:8080.

Use the application to create a new owner with a pet. Then we can test that the persistence is working by restarting the containers with docker stop and docker rm commands.

After testing, stop and remove both containers, as well as the user-defined network, to prepare for the next step:

$ docker stop pet-app-prod
pet-app-prod
$ docker stop pet-db
pet-db
$ docker rm pet-app-prod
pet-app-prod
$ docker rm pet-db
pet-db
$ docker network rm pet-net
pet-net