Pass configs to Kubernetes using ConfigMap

Introduction

Today we will learn about ConfigMap Resource of Kubernetes. This is used to pass the configs to Kubernetes resources like Pod, Deployment etc.

ConfigMap

We will create a ConfigMap using yaml:

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config
  namespace: default
data:
  special.how: very
  log_level: INFO
  SPECIAL_LEVEL: very
  SPECIAL_TYPE: charm
  example.property.file: |-
    property.1=value-1
    property.2=value-2
    property.3=value-3    

We will create the config from above yaml:

$ kubectl apply -f config.yaml
configmap/special-config created

We will use this config in below pod:

apiVersion: v1
kind: Pod
metadata:
  name: ashok-config-pod
spec:
  containers:
    - name: ashok-config-pod
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "env" ]
      env:
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: special.how
        - name: LOG_LEVEL
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: log_level
  restartPolicy: Never

Let's apply above yaml:

$ kubectl apply -f pod.yaml
pod/ashok-config-pod created

We can check the status of the pod:

$ kubectl get po
NAME               READY   STATUS      RESTARTS   AGE
ashok-config-pod   0/1     Completed   0          48s

We can see the status is  completed for our pod. To check our configs passed as environment variables will be visible in the logs.

$ kubectl logs ashok-config-pod
KUBERNETES_SERVICE_PORT=443
KUBERNETES_PORT=tcp://10.96.0.1:443
LOG_LEVEL=INFO                         <--- Our config from the ConfigMap Resource
HOSTNAME=ashok-config-pod
SHLVL=1
HOME=/root
ASHOK_SVC_SERVICE_HOST=10.106.81.159 
KUBERNETES_PORT_443_TCP_ADDR=10.96.0.1
ASHOK_SVC_PORT=tcp://10.106.81.159:80
ASHOK_SVC_SERVICE_PORT=80
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
KUBERNETES_PORT_443_TCP_PORT=443
KUBERNETES_PORT_443_TCP_PROTO=tcp
ASHOK_SVC_PORT_80_TCP_ADDR=10.106.81.159
SPECIAL_LEVEL_KEY=very                 <--- Our config from the ConfigMap Resource
ASHOK_SVC_PORT_80_TCP_PORT=80
ASHOK_SVC_PORT_80_TCP_PROTO=tcp
KUBERNETES_SERVICE_PORT_HTTPS=443
KUBERNETES_PORT_443_TCP=tcp://10.96.0.1:443
PWD=/
KUBERNETES_SERVICE_HOST=10.96.0.1
ASHOK_SVC_PORT_80_TCP=tcp://10.106.81.159:80

We will use another pod yaml to see the example.property.file :

apiVersion: v1
kind: Pod
metadata:
  name: ashok-config-pod
spec:
  containers:
    - name: ashok-config-pod
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "ls /etc/config/" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        # Provide the name of the ConfigMap containing the files you want
        # to add to the container
        name: special-config
  restartPolicy: Never

Similarly you can check the configs in logs.

Happy Coding !!