Flyway is a database migration tool. We will use the flyway migration scripts that will migrate our database from our local workstation to a container running an init container, which will run the migration scripts before starting our REST API.

We will work with PostgreSQL ^14 as our primary database, so we would need to setup our local environment accordingly.

NOTE: The steps mentioned below are only for MacOS. For other distros, please refer to the official Postgresql documentation.

• Install postgres locally:

brew install postgresql@15
# validate installation
psql --version

• After postgres is installed, we need the postgres service up and running:

brew service start postgres@15

• Let's start by connecting to the default postgres database:

psql postgres

• Create a role in postgres and assign permissions:

CREATE ROLE <user> WITH LOGIN PASSWORD <user_password>;
ALTER ROLE <user> CREATEDB;
# if required, add other permissions as well: REPLICATION, CREATEROLE, etc
\du # to list all users and permissions
\q # quit postgres cli

• Connect to postgres db using new role created, create and connect to a new database:

# connect to db using new user
psql -d postgres -U <user>
# create a database
CREATE DATABASE <db_name>;
\c <db_name> # connect to new db

NOTE: The steps mentioned below are only for MacOS. For other distros, please refer to the official Flyway documentation.

• Install flyway locally:

  brew install flyway
  # verify installation
  flyway version

• Creating migration scripts: Migration scripts ending with .sql are the scripts used to migrate/setup our database using flyway for SQL based migrations. These should be placed in a folder called sql, with proper naming conventions as mentioned in the documentation.

• Create a flyway.conf migration configuration file: This file contains the database connection URL, which connects to our database instance/service. It also contains the username and password for the database we connect to and run the migrations on. For more details on the configuration file, refer this documentation. Alternatively, you can also follow the example.flyway.conf file for configuration options.

• Using environment variables: Since we will use the kubernetes Secret resource to configure our flyway environment variables, we just need to follow the naming convention for the variables in the flyway.conf configuration file:

  flyway.url=${DB_FLYWAY_CONNECTION_URL}
  flyway.user=${DB_FLYWAY_USERNAME}
  flyway.password=${DB_FLYWAY_PASSWORD}

• To run migrations locally on a postgres service, we can configure the migration options in the flyway.conf file and run the migrate command.

  flyway migrate

NOTE: If the migrations are already performed, or there are no migrations to be performed, flyway returns a no-op.

Here, we containerize the migration scripts and configuration files into a docker image. Since this image will run within an initContainer in a k8s deployment, this docker image does not need to run any CMD to run the migrations (since this will be done within the initContainer). A .dockerignore file is also needed to prevent copying files and folders that are not required in the final build image.