How to Deploy Micronaut on Platform.sh with MongoDB
Contents:
To activate MongoDB and then have it accessed by the Micronaut application already in Platform.sh, it is necessary to modify two files.
Note:
This guide only covers the addition of a MongoDB service configuration to an existing Micronaut project already configured to deploy on Platform.sh. Please see the deployment guide for more detailed instructions for setting up app containers and initial projects.
1. Add the MongoDB service 
In your .platform/services.yaml file, include MongoDB with a valid supported version:
dbmongo:
type: mongodb:3.6
disk: 512
2. Grant access to MongoDb through a relationship
In your .platform.app.yaml file, use the service name dbmongo to grant the application access to MongoDB via a relationship:
relationships:
mongodatabase: "dbmongo:mongodb"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 databse into it’s own environment variables that can be easily used by Micronaut. On Platform.sh, custom environment variables can be defined programmatically in a .environment file using jq to do just that:
export MONGO_PORT=`echo $PLATFORM_RELATIONSHIPS|base64 -d|json_pp|jq -r ".mongodb[0].port"`
export MONGO_HOST=`echo $PLATFORM_RELATIONSHIPS|base64 -d|json_pp|jq -r ".mongodb[0].host"`
export MONGO_PASSWORD=`echo $PLATFORM_RELATIONSHIPS|base64 -d|json_pp|jq -r ".mongodb[0].password"`
export MONGO_USER=`echo $PLATFORM_RELATIONSHIPS|base64 -d|json_pp|jq -r ".mongodb[0].username"`
export MONGO_DATABASE=`echo $PLATFORM_RELATIONSHIPS|base64 -d|json_pp|jq -r ".mongodb[0].path"`
export MONGO_URL=mongodb://${MONGO_USER}:${MONGO_PASSWORD}@${MONGO_HOST}:${MONGO_PORT}/${MONGO_DATABASE}
export JAVA_OPTS="-Xmx$(jq .info.limits.memory /run/config.json)m -XX:+ExitOnOutOfMemoryError"
Tip:
Environment variable names are following the conversion rules of the Micronaut Documentation.
4. Connect to the service
Commit that code and push. The application is ready and connected to a MongoDB instance.