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2-persistent-volume.md

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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 linking containers

Acceptance Criteria

  • Application configuration modified to connect to MySQL database
  • Docker image is rebuilt and tagged as pet-app
  • MySQL running 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

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

$ docker run --name=pet-app-prod -d -p 8080:8080 -e "SPRING_PROFILES_ACTIVE=mysql" --link pet-db 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 to prepare for the next step.