How to add protocol prefix in Kubernetes ConfigMap - postgresql

Question

In my Kubernetes cluster, I have a ConfigMap object containing the address of my Postgres pod. It was created with the following YAML:
apiVersion: v1
kind: ConfigMap
metadata:
name: postgres-configmap
data:
database_url: postgres-service
Now I reference this value in one of my Deployment's configuration:
env:
- name: DB_ADDRESS
valueFrom:
configMapKeyRef:
name: postgres-configmap
key: database_url
This deployment is a Spring Boot application that intends to communicate with the database. Thus it reads the database's URL from the DB_ADDRESS environment variable. (ignore the default values, those are used only during development)
datasource:
url: ${DB_ADDRESS:jdbc:postgresql://localhost:5432/users}
username: ${POSTGRES_USER:postgres}
password: ${POSTGRES_PASSWORD:mysecretpassword}
So, according to the logs, the problem is that the address has to have the jdbc:postgresql:// prefix. Either in the ConfigMap's YAML or in the application.yml I would need to concatenate the prefix protocol string with the variable. Any idea how to do it in yml or suggestion of some other workaround?

Answer 1

If you create a Service, that will provide you with a hostname (the name of the service) that you can then use in the ConfigMap. E.g., if you create a service named postgres, then your ConfigMap would look like:
apiVersion: v1
kind: ConfigMap
metadata:
name: postgres-configmap
data:
database_url: jdbc:postgresql://postgres:5432/users

Answer 2

Kubernetes environment variable declarations can embed the values of other environment variables. This is the only string manipulation that Kubernetes supports, and it pretty much only works in env: blocks.
For this setup, once you've retrieved the database hostname from the ConfigMap, you can then embed it into a more complete SPRING_DATASOURCE_URL environment variable:
env:
- name: DB_ADDRESS
valueFrom:
configMapKeyRef:
name: postgres-configmap
key: database_url
- name: SPRING_DATASOURCE_URL
value: 'jdbc:postgresql://$(DB_ADDRESS):5432/users'
You might similarly parameterize the port (though it will almost always be the standard port 5432) and database name. Avoid putting these settings in a Spring profile YAML file, where you'll have to rebuild your application if any of the deploy-time settings change.