In my simple database application (see docker example post]) Java application is connecting to postgresql database. When the container starts, it creates a database named
What is the best practice when it comes to distributing my application as docker image and using it as a docker container?
Here is my usecase.
I want to create the tables and initialize them with my data (i.e. stoic quotes). However, if the same container is started again (with the same volume), I expect the same data to stay there, together with all changes made by user.
How to achieve this? First, I need to learn about docker volumes.
Then, I need to think about schema creation. I cannot create tables on application start, so hibernate.hbm2ddl.auto certainly should not have the value create-only/create/create-drop (see explanation of ddl-auto values on SO and Vlad Michalcea blog post on schema generation)
What are my options? I could either create init.sql script (which is not recommended) or use a soltion like Liquibase library where I would write a script for both DDL changes and database initialization. Liquibase seems like a good idea and I plan to follow Liquibase tutorial on Spring-boot and maven and Liquibase.
DDL from JPA model
In order to peek on the DDL statements, I decided to run
mvn spring-boot:start -Dspring-boot.run.jvmArguments="-Dspring.jpa.hibernate.ddl-auto=create -Ddebug=true"
so that all DDL commands (tables that are created from scratch, constraints, indexes if any) are written to spring boot logs.
Liquibase for schema creation and initialization
Then, I removed
spring.jpa.hibernate.ddl-auto=create from application.properties and added Liquibase property
spring.liquibase.change-log=classpath:db/changelog/changelog.sql instead, added Liquibase dependency and actual
changelog.sql where I put all the DDL statements I found in previous step.
My application.properties look like this:
pom.xml gained one dependency:
And changelog.sql is very simple:
Add volumes to postgresql docker-compose service
In order for postgresql docker container to use external volume, I also modified
docker-compose.yaml and added
volumes key inside
db service specification. This way I can rebuild my application image and be sure that Liquibase correctly applies all the changeset I need (with DDL) in case it is run on virgin new database.
Try it out
Let’s build the app:
And I have exactly what I wanted:
Now, let’s add a thought:
Things I have learned
Pass spring boot parameters to maven
If I want to overwrite one of properties declared in application.properties, I can do it when I start spring boot application. For example, if I want to activate dev profile, I could do:
mvn spring-boot:run -Dspring-boot.run.jvmArguments="-Dspring.profiles.active=dev"
or, in my case, if I want to check what DDL statements
mvn spring-boot:start -Dspring-boot.run.jvmArguments="-Dspring.jpa.hibernate.ddl-auto=none -Ddebug=true"
(found here, on SO)
Use Liquibase with spring-boot
This is as simple as following the Liquibase tutorial. This is a list of steps I followed:
- creating subdirectories structure
src/main/resourceswhere I just put single
- add maven dependency to Liquibase
Define a volume in docker-compose.yml
I found an example in this blog post in which a database is created and initialized with .sql init script which is placed in
/docker-entrypoint-initb.d (as explained in postgres docker image documentation.
Add volumes definition to compose file
I didn’t want to add it this way but rather have more control over data and schema changes locally. Therefore I decided to use Liquibase. Neverheless, I needed to define a volume for postgresql so that data is kept safe between containers’ restarts. It was enough to just add:
and the database is stored in postgres-data directory located at the current directory from where docker-compose starts.
I’ve set up liquibase with spring-boot app that takes care of schema creation and possibly future migrations. I added volume definition to docker-compose file so that postgresql always has access to the same database. I’ve also learned how to enable debug logs (with hibernate SQL statements) and overwrite spring boot properties when application is run with maven from commandline.
Project on github
I called it stoic_cafe: Let’s push it: https://github.com/kamchy/stoic_cafe
- SO answer on spring boot + Liquibase with xml
- Liquibase change types - reference - I might use it later, right now I just use pure SQL
- creating and filling postgresql with docker-compose
Ten wpis jest częścią serii docker.
- 2022-21-09 - Dockerize Spring Boot App with Frontend in React
- 2022-15-09 - Docker Volumes
- 2022-28-04 - Dockerize Spring Boot REST Service with Postgresql on Docker