Cloud-Native Microservices With Kubernetes - 2nd Edition

Consuming ConfigMaps

We previously created a ConfigMap named postgres-config that contains the environment variables required to configure PostgreSQL. Now, we will see how to consume it.

When creating a Pod, we can specify the ConfigMap in the Pod specification. Kubernetes will then inject the ConfigMap data into the Pod as environment variables or as files in a volume.

This is how to define this in YAML:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: postgres
  namespace: postgres
spec:
  replicas: 1
  selector:
    matchLabels:
      app: postgres
  template:
    metadata:
      labels:
        app: postgres
    spec:
      containers:
        - name: postgres
          image: postgres:18
          # Tell Kubernetes to always pull the image
          # even if it is already present on the node
          imagePullPolicy: Always
          ports:
            - containerPort: 5432
          envFrom:
            - configMapRef:
                name: postgres-config

The envFrom field in the container specification tells Kubernetes to inject all the key-value pairs from the ConfigMap named postgres-config as environment variables in the container. Our ConfigMap should now be consumed by the PostgreSQL container. To add more variables, we can simply update the ConfigMap without needing to modify the Deployment—only restart its Pods (kubectl rollout restart deployment postgres -n postgres).

An alternative way to add environment variables is to use the env field in the container specification. This way, we can specify each environment variable individually. Here is an example:

apiVersion