Demo Config Maps

This lesson demonstrates how to create and consume a Kubernetes ConfigMap from a Deployment (example: CartsDB). You’ll see:

The ConfigMap manifest and the key/value pairs it stores.
The relevant Deployment snippet that consumes those keys via configMapKeyRef.
The commands and expected behavior when the Deployment is applied before the ConfigMap exists, and what changes after the ConfigMap is created.

ConfigMap manifest

File: carts-configmap.yaml

apiVersion: v1
kind: ConfigMap
metadata:
  name: cartsdb-config
data:
  MONGODB_USER: "sock-user"
  MONGODB_DATABASE: "data"

This ConfigMap stores simple key/value pairs:

Key	Value
`MONGODB_USER`	`sock-user`
`MONGODB_DATABASE`	`data`

ConfigMaps are intended for non-sensitive configuration data. For secrets, use Kubernetes Secrets instead.

Deployment snippet that consumes the ConfigMap

File: carts-db-deployment.yaml This is the essential part of the Deployment that consumes the ConfigMap values via configMapKeyRef. It focuses on the container, ports, and environment variables:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: carts-db
  labels:
    name: carts-db
spec:
  replicas: 1
  selector:
    matchLabels:
      name: carts-db
  template:
    metadata:
      labels:
        name: carts-db
    spec:
      containers:
      - name: carts-db
        image: centos/mongodb-34-centos7
        ports:
          - containerPort: 27017
        env:
          - name: MONGODB_USER
            valueFrom:
              configMapKeyRef:
                name: cartsdb-config
                key: MONGODB_USER
          - name: MONGODB_PASSWORD
            value: password
          - name: MONGODB_DATABASE
            valueFrom:
              configMapKeyRef:
                name: cartsdb-config
                key: MONGODB_DATABASE
          - name: MONGODB_ADMIN_PASSWORD
            value: admin
        volumeMounts:
          - mountPath: /tmp
            name: tmp-volume
      volumes:
        - name: tmp-volume
          emptyDir: {}

Note how env.valueFrom.configMapKeyRef references both:

the ConfigMap resource name: cartsdb-config
the specific key within it: MONGODB_USER and MONGODB_DATABASE

The ConfigMap must exist in the same namespace so the kubelet can populate those environment variables when creating the container.

A ConfigMap is a separate Kubernetes resource. If the Deployment references a ConfigMap that does not exist when the Pod is created, the Pod will fail to start with an error like CreateContainerConfigError until the ConfigMap is created.

Reproduce the failure (apply Deployment before ConfigMap)

Try deploying the Deployment before creating the ConfigMap to observe the failure:

# Apply the Deployment (without having created the ConfigMap)
oc apply -f carts-db-deployment.yaml

When the referenced ConfigMap doesn’t exist, the Pod will fail to start. In the OpenShift console the Pod status will show CreateContainerConfigError (example screenshot):

Screenshot of the Red Hat OpenShift web console showing the "Pods" view in the default project. A pod named "carts-db-67d8869bbf-..." is listed with status "CreateContainerConfigError" and 0/1 ready.

Inspect the Pod events in the console or run:

# Describe the failing Pod to see the event saying the ConfigMap was not found
oc describe pod `oc get pod -l name=carts-db -o name` 
# Or target a specific pod:
# oc describe pod `oc get pod -l name=carts-db -o jsonpath='{.items[0].metadata.name}'`

You will see an event explaining that the ConfigMap cartsdb-config was not found.

Create the ConfigMap and recover the Pod

Create the ConfigMap, then reapply the Deployment or delete the failed Pod so the ReplicaSet recreates it:

# Create the ConfigMap
oc apply -f carts-configmap.yaml

# Optionally reapply the Deployment (harmless) or delete the failed pod to trigger a recreate:
oc apply -f carts-db-deployment.yaml
# Or delete the Pod to let the Deployment create a new one:
# oc delete pod -l name=carts-db

Example output when creating the ConfigMap:

$ oc apply -f carts-configmap.yaml
configmap/cartsdb-config created

After the ConfigMap exists, the Pod can resolve the referenced keys and should transition to Running. Example OpenShift console view showing the Pod in Running state:

A screenshot of the Red Hat OpenShift web console showing Pod details for "carts-db-67d8869bbf-nk974" in the "default" project with status "Running." The page displays metadata like namespace, labels, restart policy and Pod IP, with the left sidebar highlighting Workloads → Pods.

You can also inspect the Pod YAML to confirm metadata and IP information:

status:
  podIP: 10.217.0.183
  podIPs:
    - ip: 10.217.0.183
metadata:
  resourceVersion: "83802"
  name: carts-db-67d8869bbf-nk974
  uid: ec5385a7-a1a0-468a-88c6-ef277eba3561

Quick reference

Resource	Purpose	Example command
ConfigMap	Store non-sensitive configuration as key/value pairs	`oc apply -f carts-configmap.yaml`
Deployment	Consume ConfigMap via `env.valueFrom.configMapKeyRef`	`oc apply -f carts-db-deployment.yaml`
Pod troubleshooting	View events when Pod fails to start	`oc describe pod <pod-name>`

Links and further reading

Summary

Store non-sensitive configuration data in a ConfigMap as key/value pairs.
Reference ConfigMap values from a Pod using env.valueFrom.configMapKeyRef.
Ensure the ConfigMap exists before the Pod is created; otherwise the Pod will fail with CreateContainerConfigError.
For secrets or sensitive information, use Kubernetes Secrets instead of ConfigMaps.

Do not store sensitive credentials in a ConfigMap. Use Kubernetes Secrets for passwords, tokens, and private keys.

Introduction

Pre-Requisite – Docker and Kubernetes

Getting Started with OpenShift

OpenShift Concepts – Projects and Users

Concepts – Builds and Deployments

Networks, Services, Routes and Scaling

Storage, Templates and Catalog

OpenShift Security

Conclusion and APPENDIX

ConfigMap manifest

Deployment snippet that consumes the ConfigMap

Reproduce the failure (apply Deployment before ConfigMap)

Create the ConfigMap and recover the Pod

Quick reference

Links and further reading

Summary

Watch Video

​ConfigMap manifest

​Deployment snippet that consumes the ConfigMap

​Reproduce the failure (apply Deployment before ConfigMap)

​Create the ConfigMap and recover the Pod

​Quick reference

​Links and further reading

​Summary

Watch Video

ConfigMap manifest

Deployment snippet that consumes the ConfigMap

Reproduce the failure (apply Deployment before ConfigMap)

Create the ConfigMap and recover the Pod

Quick reference

Links and further reading

Summary