Configuring Redis using a ConfigMap

This page provides a real world example of how to configure Redis using a ConfigMap and builds upon the Configure a Pod to Use a ConfigMap task.

Objectives

• Create a ConfigMap with Redis configuration values
• Create a Redis Pod that mounts and uses the created ConfigMap
• Verify that the configuration was correctly applied.

Before you begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:

• Killercoda
• KodeKloud
• Play with Kubernetes

To check the version, enter kubectl version.

• The example shown on this page works with kubectl 1.14 and above.
• Understand Configure a Pod to Use a ConfigMap.

Real World Example: Configuring Redis using a ConfigMap

Follow the steps below to configure a Redis cache using data stored in a ConfigMap.

First create a ConfigMap with an empty configuration block:

cat <<EOF >./example-redis-config.yaml apiVersion: v1 kind: ConfigMap metadata:  name: example-redis-config data:  redis-config: "" EOF 

Apply the ConfigMap created above, along with a Redis pod manifest:

kubectl apply -f example-redis-config.yaml kubectl apply -f https://raw.githubusercontent.com/kubernetes/website/main/content/en/examples/pods/config/redis-pod.yaml 

Examine the contents of the Redis pod manifest and note the following:

• A volume named config is created by spec.volumes[1]
• The key and path under spec.volumes[1].configMap.items[0] exposes the redis-config key from the example-redis-config ConfigMap as a file named redis.conf on the config volume.
• The config volume is then mounted at /redis-master by spec.containers[0].volumeMounts[1].

This has the net effect of exposing the data in data.redis-config from the example-redis-config ConfigMap above as /redis-master/redis.conf inside the Pod.

pods/config/redis-pod.yaml

apiVersion: v1 kind: Pod metadata:  name: redis spec:  containers:  - name: redis  image: redis:8.0.2  command:  - redis-server  - "/redis-master/redis.conf"  env:  - name: MASTER  value: "true"  ports:  - containerPort: 6379  resources:  limits:  cpu: "0.1"  volumeMounts:  - mountPath: /redis-master-data  name: data  - mountPath: /redis-master  name: config  volumes:  - name: data  emptyDir: {}  - name: config  configMap:  name: example-redis-config  items:  - key: redis-config  path: redis.conf 

Examine the created objects:

kubectl get pod/redis configmap/example-redis-config 

You should see the following output:

NAME READY STATUS RESTARTS AGE pod/redis 1/1 Running 0 8s NAME DATA AGE configmap/example-redis-config 1 14s 

Recall that we left redis-config key in the example-redis-config ConfigMap blank:

kubectl describe configmap/example-redis-config 

You should see an empty redis-config key:

Name: example-redis-config Namespace: default Labels: <none> Annotations: <none>  Data ==== redis-config: 

Use kubectl exec to enter the pod and run the redis-cli tool to check the current configuration:

kubectl exec -it redis -- redis-cli 

Check maxmemory:

127.0.0.1:6379> CONFIG GET maxmemory 

It should show the default value of 0:

1) "maxmemory" 2) "0" 

Similarly, check maxmemory-policy:

127.0.0.1:6379> CONFIG GET maxmemory-policy 

Which should also yield its default value of noeviction:

1) "maxmemory-policy" 2) "noeviction" 

Now let's add some configuration values to the example-redis-config ConfigMap:

pods/config/example-redis-config.yaml

apiVersion: v1 kind: ConfigMap metadata:  name: example-redis-config data:  redis-config: |  maxmemory 2mb  maxmemory-policy allkeys-lru 

Apply the updated ConfigMap:

kubectl apply -f example-redis-config.yaml 

Confirm that the ConfigMap was updated:

kubectl describe configmap/example-redis-config 

You should see the configuration values we just added:

Name: example-redis-config Namespace: default Labels: <none> Annotations: <none>  Data ==== redis-config: ---- maxmemory 2mb maxmemory-policy allkeys-lru 

Check the Redis Pod again using redis-cli via kubectl exec to see if the configuration was applied:

kubectl exec -it redis -- redis-cli 

Check maxmemory:

127.0.0.1:6379> CONFIG GET maxmemory 

It remains at the default value of 0:

1) "maxmemory" 2) "0" 

Similarly, maxmemory-policy remains at the noeviction default setting:

127.0.0.1:6379> CONFIG GET maxmemory-policy 

Returns:

1) "maxmemory-policy" 2) "noeviction" 

The configuration values have not changed because the Pod needs to be restarted to grab updated values from associated ConfigMaps. Let's delete and recreate the Pod:

kubectl delete pod redis kubectl apply -f https://raw.githubusercontent.com/kubernetes/website/main/content/en/examples/pods/config/redis-pod.yaml 

Now re-check the configuration values one last time:

kubectl exec -it redis -- redis-cli 

Check maxmemory:

127.0.0.1:6379> CONFIG GET maxmemory 

It should now return the updated value of 2097152:

1) "maxmemory" 2) "2097152" 

Similarly, maxmemory-policy has also been updated:

127.0.0.1:6379> CONFIG GET maxmemory-policy 

It now reflects the desired value of allkeys-lru:

1) "maxmemory-policy" 2) "allkeys-lru" 

Clean up your work by deleting the created resources:

kubectl delete pod/redis configmap/example-redis-config 

What's next

• Learn more about ConfigMaps.
• Follow an example of Updating configuration via a ConfigMap.