How to Deploy Micronoaut on with JPA

To activate JPA and then have it accessed by the Micronoaut application already configured for, it is necessary to modify two files.

1. Add a SQL database service 

In your service configuration, include a SQL database service. Make sure to visit the documentation for that service to find a valid version. For PostgreSQL that would look like:

    type: postgresql:14
    disk: 256

2. Grant access to the service through a relationship 

To access the new service, set a relationship in your app configuration.
    postgresdatabase: "dbpostgres:postgresql"

3. Export connection credentials to the environment 

Connection credentials for services are exposed to the application container through the PLATFORM_RELATIONSHIPS environment variable from the deploy hook onward. Since this variable is a base64 encoded JSON object of all of your project’s services, you’ll likely want a clean way to extract the information specific to the database into it’s own environment variables that can be used by Micronaut. On, custom environment variables can be defined programmatically in a .environment file using jq to do just that:

export JDBC_HOST=`echo $PLATFORM_RELATIONSHIPS|base64 -d|jq -r ".database[0].host"`
export JDBC_PORT=`echo $PLATFORM_RELATIONSHIPS|base64 -d|jq -r ".database[0].port"`
export DATABASE=`echo $PLATFORM_RELATIONSHIPS|base64 -d|jq -r ".database[0].path"`
export DATASOURCES_DEFAULT_PASSWORD=`echo $PLATFORM_RELATIONSHIPS|base64 -d|jq -r ".database[0].password"`
export DATASOURCES_DEFAULT_USERNAME=`echo $PLATFORM_RELATIONSHIPS|base64 -d|jq -r ".database[0].username"`
export JAVA_OPTS="-Xmx$(jq .info.limits.memory /run/config.json)m -XX:+ExitOnOutOfMemoryError"

4. Connect to the service 

Commit that code and push. The specified cluster will now always point to the PostgreSQL or any SQL service that you wish.