Concating values from configMap and secret - kubernetes

Question

I have a configMap file:
apiVersion: v1
kind: ConfigMap
metadata:
labels:
owner: testdb
name: testdb-configmap
data:
host: postgres
port: "5432"
and a secret file:
aapiVersion: v1
kind: Secret
type: Opaque
metadata:
labels:
owner: testdb
name: testdb-secret
namespace: test
data:
user: dGVzdA==
pwd: dGVzdA==
and I want to build an environment variable CONNECTION_STRING as below:
env:
- name: CONNECTION_STRING
value: "Host=<host-from-configmap>;Username=<user-from-secret>;Password=<password-from-secret>;Port=<port-from-configmap>;Pooling=False;"
I want to know if this is possible and if yes, then how? I have also looked at using .tpl (named templates) but couldn't figure out a way.
NOTE
Since I don't have access to the image which requires CONNECTION_STRING I have to build it this way. These configmap and secret files are also going to remain like this.

Answer 1

Kubernetes can set environment variables based on other environment variables. This is a core Kubernetes Pod capability, and doesn't depend on anything from Helm.
Your value uses four components, two from the ConfigMap and two from the Secret. You need to declare each of these as separate environment variables, and then declare a main environment variable that concatenates them together.
env:
- name: TESTDB_HOST
valueFrom:
configMapRef:
name: testdb-configmap # {{ include "chart.name" . }}
key: host
- name: TESTDB_PORT
valueFrom:
configMapRef:
name: testdb-configmap
key: port
- name: TESTDB_USER
valueFrom:
secretKeyRef:
name: testdb-secret
key: user
- name: TESTDB_PASSWORD
valueFrom:
secretKeyRef:
name: testdb-secret
key: password
- name: CONNECTION_STRING
value: Host=$(TESTDB_HOST);Username=$(TESTDB_USER);Password=$(TESTDB_PASSWORD);PORT=$(TESTDB_PORT);Pooling=False;

Answer 2

I do not believe what you're asking to do is possible.
Furthermore, do not use configs maps for storing information like this. It's best practice to use secrets and then mount them to your container as files or ENV variables.
I would abandon whatever you're thinking and re-evaluate what you're trying to accomplish.