postfix container kubernetes - setting up encrypted secret, configmap for successful db connection

I am trying to run postfix as a container in k8s. The container starts (including the svcs) but my config maps and secrets don't want to play nice. I tried the following:

1. setup the config map with the user and password in clear text RESULT: WORKS postmap -q someuser@localhost mysql:./virtual_mailbox.cf
2. Encrypt the password and username with base64 (as per k8s instructions), read these encrypted values into the environment variables of the container (envFrom:- secretRef: name: postfix-db-access), try to connect to the database with postmap For this scenario the config map looks like the following:

  1 apiVersion: v1
  2 kind: ConfigMap
  3 metadata:
  4   name: postfix-db-configs
  5   namespace: mailserver
  6 data:
  7   virtual_mailbox.cf: |
  8     user=$(echo ${POSTFIX_USER} | base64 -d)
  9     password=$(echo ${POSTFIX_PASS} | base64 -d)
 10     hosts=database.default.svc.cluster.local
 11     dbname=postfix
 12     query=SELECT mail FROM generic_map WHERE local_mail='%s' AND active=1;

RESULT: FAILS. User '$(echo ${POSTFIX_USER} | base64 -d)' has no access to the database.

3. Store the username and password for the postfix user in clear text in the secret like this:

  1 apiVersion: v1
  2 kind: Secret
  3 metadata:
  4     name: postfix-db-access
  5     namespace: mailserver
  6 type: Opaque
  7 stringData:
  8      POSTFIX_USER: PostfixUser
  9      POSTFIX_PASS: somePassword

and the corresponding line in the config map

    user=$(echo ${POSTFIX_USER})

RESULT: FAILS with user 'echo ${POSTFIX_USER}) has no access to the database'. The request does not process the environment variable, which is set correctly.

Connecting to the database and querying works fine with the command mysql -h database.default.svc.cluster.local -u postfix -p -e 'use postfix;SELECT mail FROM generic_map WHERE local_mail='someuser@localhost' AND active=1;. I get all the results I need and expect.

The question is: how do I setup the secret and the config map so this process works and establishes the connection to the database as intended?

realshadow

This is a community wiki answer posted for better visibility. Feel free to expand it.

Possible solution from @mdaniel:

To use pre-processed values for POSTFIX_USER, POSTFIX_PASS and etc., you can use an init container with Volume, that the init container and the application container share.

More information is available on the Kubernetes website