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Configuration

1: Example: Configuring a Java Microservice

1.1: Externalizing config using MicroProfile, ConfigMaps and Secrets

2: Updating Configuration via a ConfigMap
3: Configuring Redis using a ConfigMap

1 - Example: Configuring a Java Microservice

1.1 - Externalizing config using MicroProfile, ConfigMaps and Secrets

In this tutorial you will learn how and why to externalize your microservice’s configuration. Specifically, you will learn how to use Kubernetes ConfigMaps and Secrets to set environment variables and then consume them using MicroProfile Config.

Before you begin

Creating Kubernetes ConfigMaps & Secrets

There are several ways to set environment variables for a Docker container in Kubernetes, including: Dockerfile, kubernetes.yml, Kubernetes ConfigMaps, and Kubernetes Secrets. In the tutorial, you will learn how to use the latter two for setting your environment variables whose values will be injected into your microservices. One of the benefits for using ConfigMaps and Secrets is that they can be re-used across multiple containers, including being assigned to different environment variables for the different containers.

ConfigMaps are API Objects that store non-confidential key-value pairs. In the Interactive Tutorial you will learn how to use a ConfigMap to store the application's name. For more information regarding ConfigMaps, you can find the documentation here.

Although Secrets are also used to store key-value pairs, they differ from ConfigMaps in that they're intended for confidential/sensitive information and are stored using Base64 encoding. This makes secrets the appropriate choice for storing such things as credentials, keys, and tokens, the former of which you'll do in the Interactive Tutorial. For more information on Secrets, you can find the documentation here.

Externalizing Config from Code

Externalized application configuration is useful because configuration usually changes depending on your environment. In order to accomplish this, we'll use Java's Contexts and Dependency Injection (CDI) and MicroProfile Config. MicroProfile Config is a feature of MicroProfile, a set of open Java technologies for developing and deploying cloud-native microservices.

CDI provides a standard dependency injection capability enabling an application to be assembled from collaborating, loosely-coupled beans. MicroProfile Config provides apps and microservices a standard way to obtain config properties from various sources, including the application, runtime, and environment. Based on the source's defined priority, the properties are automatically combined into a single set of properties that the application can access via an API. Together, CDI & MicroProfile will be used in the Interactive Tutorial to retrieve the externally provided properties from the Kubernetes ConfigMaps and Secrets and get injected into your application code.

Many open source frameworks and runtimes implement and support MicroProfile Config. Throughout the interactive tutorial, you'll be using Open Liberty, a flexible open-source Java runtime for building and running cloud-native apps and microservices. However, any MicroProfile compatible runtime could be used instead.

Objectives

Create a Kubernetes ConfigMap and Secret
Inject microservice configuration using MicroProfile Config

Example: Externalizing config using MicroProfile, ConfigMaps and Secrets

Start Interactive Tutorial

2 - Updating Configuration via a ConfigMap

This page provides a step-by-step example of updating configuration within a Pod via a ConfigMap and builds upon the Configure a Pod to Use a ConfigMap task.
At the end of this tutorial, you will understand how to change the configuration for a running application.
This tutorial uses the alpine and nginx images as examples.

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:

You need to have the curl command-line tool for making HTTP requests from the terminal or command prompt. If you do not have curl available, you can install it. Check the documentation for your local operating system.

Objectives

Update configuration via a ConfigMap mounted as a Volume
Update environment variables of a Pod via a ConfigMap
Update configuration via a ConfigMap in a multi-container Pod
Update configuration via a ConfigMap in a Pod possessing a Sidecar Container

Update configuration via a ConfigMap mounted as a Volume

Use the kubectl create configmap command to create a ConfigMap from literal values:

kubectl create configmap sport --from-literal=sport=football

Below is an example of a Deployment manifest with the ConfigMap sport mounted as a volume into the Pod's only container.

deployments/deployment-with-configmap-as-volume.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: configmap-volume
  labels:
    app.kubernetes.io/name: configmap-volume
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: configmap-volume
  template:
    metadata:
      labels:
        app.kubernetes.io/name: configmap-volume
    spec:
      containers:
        - name: alpine
          image: alpine:3
          command:
            - /bin/sh
            - -c
            - while true; do echo "$(date) My preferred sport is $(cat /etc/config/sport)";
              sleep 10; done;
          ports:
            - containerPort: 80
          volumeMounts:
            - name: config-volume
              mountPath: /etc/config
      volumes:
        - name: config-volume
          configMap:
            name: sport

Create the Deployment:

kubectl apply -f https://k8s.io/examples/deployments/deployment-with-configmap-as-volume.yaml

Check the pods for this Deployment to ensure they are ready (matching by selector):

kubectl get pods --selector=app.kubernetes.io/name=configmap-volume

You should see an output similar to:

NAME                                READY   STATUS    RESTARTS   AGE
configmap-volume-6b976dfdcf-qxvbm   1/1     Running   0          72s
configmap-volume-6b976dfdcf-skpvm   1/1     Running   0          72s
configmap-volume-6b976dfdcf-tbc6r   1/1     Running   0          72s

On each node where one of these Pods is running, the kubelet fetches the data for that ConfigMap and translates it to files in a local volume. The kubelet then mounts that volume into the container, as specified in the Pod template. The code running in that container loads the information from the file and uses it to print a report to stdout. You can check this report by viewing the logs for one of the Pods in that Deployment:

# Pick one Pod that belongs to the Deployment, and view its logs
kubectl logs deployments/configmap-volume

You should see an output similar to:

Found 3 pods, using pod/configmap-volume-76d9c5678f-x5rgj
Thu Jan  4 14:06:46 UTC 2024 My preferred sport is football
Thu Jan  4 14:06:56 UTC 2024 My preferred sport is football
Thu Jan  4 14:07:06 UTC 2024 My preferred sport is football
Thu Jan  4 14:07:16 UTC 2024 My preferred sport is football
Thu Jan  4 14:07:26 UTC 2024 My preferred sport is football

Edit the ConfigMap:

kubectl edit configmap sport

In the editor that appears, change the value of key sport from football to cricket. Save your changes. The kubectl tool updates the ConfigMap accordingly (if you see an error, try again).

Here's an example of how that manifest could look after you edit it:

apiVersion: v1
data:
  sport: cricket
kind: ConfigMap
# You can leave the existing metadata as they are.
# The values you'll see won't exactly match these.
metadata:
  creationTimestamp: "2024-01-04T14:05:06Z"
  name: sport
  namespace: default
  resourceVersion: "1743935"
  uid: 024ee001-fe72-487e-872e-34d6464a8a23

You should see the following output:

configmap/sport edited

Tail (follow the latest entries in) the logs of one of the pods that belongs to this Deployment:

kubectl logs deployments/configmap-volume --follow

After few seconds, you should see the log output change as follows:

Thu Jan  4 14:11:36 UTC 2024 My preferred sport is football
Thu Jan  4 14:11:46 UTC 2024 My preferred sport is football
Thu Jan  4 14:11:56 UTC 2024 My preferred sport is football
Thu Jan  4 14:12:06 UTC 2024 My preferred sport is cricket
Thu Jan  4 14:12:16 UTC 2024 My preferred sport is cricket

When you have a ConfigMap that is mapped into a running Pod using either a configMap volume or a projected volume, and you update that ConfigMap, the running Pod sees the update almost immediately.
However, your application only sees the change if it is written to either poll for changes, or watch for file updates.
An application that loads its configuration once at startup will not notice a change.

Note: The total delay from the moment when the ConfigMap is updated to the moment when new keys are projected to the Pod can be as long as kubelet sync period.
Also check Mounted ConfigMaps are updated automatically.

Update environment variables of a Pod via a ConfigMap

Use the kubectl create configmap command to create a ConfigMap from literal values:

kubectl create configmap fruits --from-literal=fruits=apples

Below is an example of a Deployment manifest with an environment variable configured via the ConfigMap fruits.

deployments/deployment-with-configmap-as-envvar.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: configmap-env-var
  labels:
    app.kubernetes.io/name: configmap-env-var
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: configmap-env-var
  template:
    metadata:
      labels:
        app.kubernetes.io/name: configmap-env-var
    spec:
      containers:
        - name: alpine
          image: alpine:3
          env:
            - name: FRUITS
              valueFrom:
                configMapKeyRef:
                  key: fruits
                  name: fruits
          command:
            - /bin/sh
            - -c
            - while true; do echo "$(date) The basket is full of $FRUITS";
                sleep 10; done;
          ports:
            - containerPort: 80

Create the Deployment:

kubectl apply -f https://k8s.io/examples/deployments/deployment-with-configmap-as-envvar.yaml

Check the pods for this Deployment to ensure they are ready (matching by selector):

kubectl get pods --selector=app.kubernetes.io/name=configmap-env-var

You should see an output similar to:

NAME                                 READY   STATUS    RESTARTS   AGE
configmap-env-var-59cfc64f7d-74d7z   1/1     Running   0          46s
configmap-env-var-59cfc64f7d-c4wmj   1/1     Running   0          46s
configmap-env-var-59cfc64f7d-dpr98   1/1     Running   0          46s

The key-value pair in the ConfigMap is configured as an environment variable in the container of the Pod. Check this by viewing the logs of one Pod that belongs to the Deployment.

kubectl logs deployment/configmap-env-var

You should see an output similar to:

Found 3 pods, using pod/configmap-env-var-7c994f7769-l74nq
Thu Jan  4 16:07:06 UTC 2024 The basket is full of apples
Thu Jan  4 16:07:16 UTC 2024 The basket is full of apples
Thu Jan  4 16:07:26 UTC 2024 The basket is full of apples

Edit the ConfigMap:

kubectl edit configmap fruits

In the editor that appears, change the value of key fruits from apples to mangoes. Save your changes. The kubectl tool updates the ConfigMap accordingly (if you see an error, try again).

Here's an example of how that manifest could look after you edit it:

apiVersion: v1
data:
  fruits: mangoes
kind: ConfigMap
# You can leave the existing metadata as they are.
# The values you'll see won't exactly match these.
metadata:
  creationTimestamp: "2024-01-04T16:04:19Z"
  name: fruits
  namespace: default
  resourceVersion: "1749472"

You should see the following output:

configmap/fruits edited

Tail the logs of the Deployment and observe the output for few seconds:

# As the text explains, the output does NOT change
kubectl logs deployments/configmap-env-var --follow

Notice that the output remains unchanged, even though you edited the ConfigMap:

Thu Jan  4 16:12:56 UTC 2024 The basket is full of apples
Thu Jan  4 16:13:06 UTC 2024 The basket is full of apples
Thu Jan  4 16:13:16 UTC 2024 The basket is full of apples
Thu Jan  4 16:13:26 UTC 2024 The basket is full of apples

Note: Although the value of the key inside the ConfigMap has changed, the environment variable in the Pod still shows the earlier value. This is because environment variables for a process running inside a Pod are not updated when the source data changes; if you wanted to force an update, you would need to have Kubernetes replace your existing Pods. The new Pods would then run with the updated information.

You can trigger that replacement. Perform a rollout for the Deployment, using kubectl rollout:

# Trigger the rollout
kubectl rollout restart deployment configmap-env-var

# Wait for the rollout to complete
kubectl rollout status deployment configmap-env-var --watch=true

Next, check the Deployment:

kubectl get deployment configmap-env-var

You should see an output similar to:

NAME                READY   UP-TO-DATE   AVAILABLE   AGE
configmap-env-var   3/3     3            3           12m

Check the Pods:

kubectl get pods --selector=app.kubernetes.io/name=configmap-env-var

The rollout causes Kubernetes to make a new ReplicaSet for the Deployment; that means the existing Pods eventually terminate, and new ones are created. After few seconds, you should see an output similar to:

NAME                                 READY   STATUS        RESTARTS   AGE
configmap-env-var-6d94d89bf5-2ph2l   1/1     Running       0          13s
configmap-env-var-6d94d89bf5-74twx   1/1     Running       0          8s
configmap-env-var-6d94d89bf5-d5vx8   1/1     Running       0          11s

Note: Please wait for the older Pods to fully terminate before proceeding with the next steps.

View the logs for a Pod in this Deployment:

# Pick one Pod that belongs to the Deployment, and view its logs
kubectl logs deployment/configmap-env-var

You should see an output similar to the below:

Found 3 pods, using pod/configmap-env-var-6d9ff89fb6-bzcf6
Thu Jan  4 16:30:35 UTC 2024 The basket is full of mangoes
Thu Jan  4 16:30:45 UTC 2024 The basket is full of mangoes
Thu Jan  4 16:30:55 UTC 2024 The basket is full of mangoes

This demonstrates the scenario of updating environment variables in a Pod that are derived from a ConfigMap. Changes to the ConfigMap values are applied to the Pod during the subsequent rollout. If Pods get created for another reason, such as scaling up the Deployment, then the new Pods also use the latest configuration values; if you don't trigger a rollout, then you might find that your app is running with a mix of old and new environment variable values.

Update configuration via a ConfigMap in a multi-container Pod

Use the kubectl create configmap command to create a ConfigMap from literal values:

kubectl create configmap color --from-literal=color=red

Below is an example manifest for a Deployment that manages a set of Pods, each with two containers. The two containers share an emptyDir volume that they use to communicate. The first container runs a web server (nginx). The mount path for the shared volume in the web server container is /usr/share/nginx/html. The second helper container is based on alpine, and for this container the emptyDir volume is mounted at /pod-data. The helper container writes a file in HTML that has its content based on a ConfigMap. The web server container serves the HTML via HTTP.

deployments/deployment-with-configmap-two-containers.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: configmap-two-containers
  labels:
    app.kubernetes.io/name: configmap-two-containers
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: configmap-two-containers
  template:
    metadata:
      labels:
        app.kubernetes.io/name: configmap-two-containers
    spec:
      volumes:
        - name: shared-data
          emptyDir: {}
        - name: config-volume
          configMap:
            name: color
      containers:
        - name: nginx
          image: nginx
          volumeMounts:
            - name: shared-data
              mountPath: /usr/share/nginx/html
        - name: alpine
          image: alpine:3
          volumeMounts:
            - name: shared-data
              mountPath: /pod-data
            - name: config-volume
              mountPath: /etc/config
          command:
            - /bin/sh
            - -c
            - while true; do echo "$(date) My preferred color is $(cat /etc/config/color)" > /pod-data/index.html;
              sleep 10; done;

Create the Deployment:

kubectl apply -f https://k8s.io/examples/deployments/deployment-with-configmap-two-containers.yaml

Check the pods for this Deployment to ensure they are ready (matching by selector):

kubectl get pods --selector=app.kubernetes.io/name=configmap-two-containers

You should see an output similar to:

NAME                                        READY   STATUS    RESTARTS   AGE
configmap-two-containers-565fb6d4f4-2xhxf   2/2     Running   0          20s
configmap-two-containers-565fb6d4f4-g5v4j   2/2     Running   0          20s
configmap-two-containers-565fb6d4f4-mzsmf   2/2     Running   0          20s

Expose the Deployment (the kubectl tool creates a Service for you):

kubectl expose deployment configmap-two-containers --name=configmap-service --port=8080 --target-port=80

Use kubectl to forward the port:

kubectl port-forward service/configmap-service 8080:8080 & # this stays running in the background

Access the service.

curl http://localhost:8080

You should see an output similar to:

Fri Jan  5 08:08:22 UTC 2024 My preferred color is red

Edit the ConfigMap:

kubectl edit configmap color

In the editor that appears, change the value of key color from red to blue. Save your changes. The kubectl tool updates the ConfigMap accordingly (if you see an error, try again).

Here's an example of how that manifest could look after you edit it:

apiVersion: v1
data:
  color: blue
kind: ConfigMap
# You can leave the existing metadata as they are.
# The values you'll see won't exactly match these.
metadata:
  creationTimestamp: "2024-01-05T08:12:05Z"
  name: color
  namespace: configmap
  resourceVersion: "1801272"
  uid: 80d33e4a-cbb4-4bc9-ba8c-544c68e425d6

Loop over the service URL for few seconds.

# Cancel this when you're happy with it (Ctrl-C)
while true; do curl --connect-timeout 7.5 http://localhost:8080; sleep 10; done

You should see the output change as follows:

Fri Jan  5 08:14:00 UTC 2024 My preferred color is red
Fri Jan  5 08:14:02 UTC 2024 My preferred color is red
Fri Jan  5 08:14:20 UTC 2024 My preferred color is red
Fri Jan  5 08:14:22 UTC 2024 My preferred color is red
Fri Jan  5 08:14:32 UTC 2024 My preferred color is blue
Fri Jan  5 08:14:43 UTC 2024 My preferred color is blue
Fri Jan  5 08:15:00 UTC 2024 My preferred color is blue

Update configuration via a ConfigMap in a Pod possessing a sidecar container

The above scenario can be replicated by using a Sidecar Container as a helper container to write the HTML file.
As a Sidecar Container is conceptually an Init Container, it is guaranteed to start before the main web server container.
This ensures that the HTML file is always available when the web server is ready to serve it.
Please see Enabling sidecar containers to utilize this feature.

If you are continuing from the previous scenario, you can reuse the ConfigMap named color for this scenario.
If you are executing this scenario independently, use the kubectl create configmap command to create a ConfigMap from literal values:

kubectl create configmap color --from-literal=color=blue

Below is an example manifest for a Deployment that manages a set of Pods, each with a main container and a sidecar container. The two containers share an emptyDir volume that they use to communicate. The main container runs a web server (NGINX). The mount path for the shared volume in the web server container is /usr/share/nginx/html. The second container is a Sidecar Container based on Alpine Linux which acts as a helper container. For this container the emptyDir volume is mounted at /pod-data. The Sidecar Container writes a file in HTML that has its content based on a ConfigMap. The web server container serves the HTML via HTTP.

deployments/deployment-with-configmap-and-sidecar-container.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: configmap-sidecar-container
  labels:
    app.kubernetes.io/name: configmap-sidecar-container
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: configmap-sidecar-container
  template:
    metadata:
      labels:
        app.kubernetes.io/name: configmap-sidecar-container
    spec:
      volumes:
        - name: shared-data
          emptyDir: {}
        - name: config-volume
          configMap:
            name: color
      containers:
        - name: nginx
          image: nginx
          volumeMounts:
            - name: shared-data
              mountPath: /usr/share/nginx/html
      initContainers:
        - name: alpine
          image: alpine:3
          restartPolicy: Always
          volumeMounts:
            - name: shared-data
              mountPath: /pod-data
            - name: config-volume
              mountPath: /etc/config
          command:
            - /bin/sh
            - -c
            - while true; do echo "$(date) My preferred color is $(cat /etc/config/color)" > /pod-data/index.html;
              sleep 10; done;

Create the Deployment:

kubectl apply -f https://k8s.io/examples/deployments/deployment-with-configmap-and-sidecar-container.yaml

Check the pods for this Deployment to ensure they are ready (matching by selector):

kubectl get pods --selector=app.kubernetes.io/name=configmap-sidecar-container

You should see an output similar to:

NAME                                           READY   STATUS    RESTARTS   AGE
configmap-sidecar-container-5fb59f558b-87rp7   2/2     Running   0          94s
configmap-sidecar-container-5fb59f558b-ccs7s   2/2     Running   0          94s
configmap-sidecar-container-5fb59f558b-wnmgk   2/2     Running   0          94s

Expose the Deployment (the kubectl tool creates a Service for you):

kubectl expose deployment configmap-sidecar-container --name=configmap-sidecar-service --port=8081 --target-port=80

Use kubectl to forward the port:

kubectl port-forward service/configmap-sidecar-service 8081:8081 & # this stays running in the background

Access the service.

curl http://localhost:8081

You should see an output similar to:

Sat Feb 17 13:09:05 UTC 2024 My preferred color is blue

Edit the ConfigMap:

kubectl edit configmap color

In the editor that appears, change the value of key color from blue to green. Save your changes. The kubectl tool updates the ConfigMap accordingly (if you see an error, try again).

Here's an example of how that manifest could look after you edit it:

apiVersion: v1
data:
  color: green
kind: ConfigMap
# You can leave the existing metadata as they are.
# The values you'll see won't exactly match these.
metadata:
  creationTimestamp: "2024-02-17T12:20:30Z"
  name: color
  namespace: default
  resourceVersion: "1054"
  uid: e40bb34c-58df-4280-8bea-6ed16edccfaa

Loop over the service URL for few seconds.

# Cancel this when you're happy with it (Ctrl-C)
while true; do curl --connect-timeout 7.5 http://localhost:8081; sleep 10; done

You should see the output change as follows:

Sat Feb 17 13:12:35 UTC 2024 My preferred color is blue
Sat Feb 17 13:12:45 UTC 2024 My preferred color is blue
Sat Feb 17 13:12:55 UTC 2024 My preferred color is blue
Sat Feb 17 13:13:05 UTC 2024 My preferred color is blue
Sat Feb 17 13:13:15 UTC 2024 My preferred color is green
Sat Feb 17 13:13:25 UTC 2024 My preferred color is green
Sat Feb 17 13:13:35 UTC 2024 My preferred color is green

Update configuration via an immutable ConfigMap that is mounted as a volume

Note:

Immutable ConfigMaps are especially used for configuration that is constant and is not expected to change over time. Marking a ConfigMap as immutable allows a performance improvement where the kubelet does not watch for changes.

If you do need to make a change, you should plan to either:

change the name of the ConfigMap, and switch to running Pods that reference the new name
replace all the nodes in your cluster that have previously run a Pod that used the old value
restart the kubelet on any node where the kubelet previously loaded the old ConfigMap

An example manifest for an Immutable ConfigMap is shown below.

configmap/immutable-configmap.yaml

apiVersion: v1
data:
  company_name: "ACME, Inc." # existing fictional company name
kind: ConfigMap
immutable: true
metadata:
  name: company-name-20150801

Create the Immutable ConfigMap:

kubectl apply -f https://k8s.io/examples/configmap/immutable-configmap.yaml

Below is an example of a Deployment manifest with the Immutable ConfigMap company-name-20150801 mounted as a volume into the Pod's only container.

deployments/deployment-with-immutable-configmap-as-volume.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: immutable-configmap-volume
  labels:
    app.kubernetes.io/name: immutable-configmap-volume
spec:
  replicas: 3
  selector:
    matchLabels:
      app.kubernetes.io/name: immutable-configmap-volume
  template:
    metadata:
      labels:
        app.kubernetes.io/name: immutable-configmap-volume
    spec:
      containers:
        - name: alpine
          image: alpine:3
          command:
            - /bin/sh
            - -c
            - while true; do echo "$(date) The name of the company is $(cat /etc/config/company_name)";
              sleep 10; done;
          ports:
            - containerPort: 80
          volumeMounts:
            - name: config-volume
              mountPath: /etc/config
      volumes:
        - name: config-volume
          configMap:
            name: company-name-20150801

Create the Deployment:

kubectl apply -f https://k8s.io/examples/deployments/deployment-with-immutable-configmap-as-volume.yaml

Check the pods for this Deployment to ensure they are ready (matching by selector):

kubectl get pods --selector=app.kubernetes.io/name=immutable-configmap-volume

You should see an output similar to:

NAME                                          READY   STATUS    RESTARTS   AGE
immutable-configmap-volume-78b6fbff95-5gsfh   1/1     Running   0          62s
immutable-configmap-volume-78b6fbff95-7vcj4   1/1     Running   0          62s
immutable-configmap-volume-78b6fbff95-vdslm   1/1     Running   0          62s

The Pod's container refers to the data defined in the ConfigMap and uses it to print a report to stdout. You can check this report by viewing the logs for one of the Pods in that Deployment:

# Pick one Pod that belongs to the Deployment, and view its logs
kubectl logs deployments/immutable-configmap-volume

You should see an output similar to:

Found 3 pods, using pod/immutable-configmap-volume-78b6fbff95-5gsfh
Wed Mar 20 03:52:34 UTC 2024 The name of the company is ACME, Inc.
Wed Mar 20 03:52:44 UTC 2024 The name of the company is ACME, Inc.
Wed Mar 20 03:52:54 UTC 2024 The name of the company is ACME, Inc.

Note: Once a ConfigMap is marked as immutable, it is not possible to revert this change nor to mutate the contents of the data or the binaryData field.
In order to modify the behavior of the Pods that use this configuration, you will create a new immutable ConfigMap and edit the Deployment to define a slightly different pod template, referencing the new ConfigMap.

Create a new immutable ConfigMap by using the manifest shown below:

configmap/new-immutable-configmap.yaml

apiVersion: v1
data:
  company_name: "Fiktivesunternehmen GmbH" # new fictional company name
kind: ConfigMap
immutable: true
metadata:
  name: company-name-20240312

kubectl apply -f https://k8s.io/examples/configmap/new-immutable-configmap.yaml

You should see an output similar to:

configmap/company-name-20240312 created

Check the newly created ConfigMap:

kubectl get configmap

You should see an output displaying both the old and new ConfigMaps:

NAME                    DATA   AGE
company-name-20150801   1      22m
company-name-20240312   1      24s

Modify the Deployment to reference the new ConfigMap.

Edit the Deployment:

kubectl edit deployment immutable-configmap-volume

In the editor that appears, update the existing volume definition to use the new ConfigMap.

volumes:
- configMap:
    defaultMode: 420
    name: company-name-20240312 # Update this field
  name: config-volume

You should see the following output:

deployment.apps/immutable-configmap-volume edited

This will trigger a rollout. Wait for all the previous Pods to terminate and the new Pods to be in a ready state.

Monitor the status of the Pods:

kubectl get pods --selector=app.kubernetes.io/name=immutable-configmap-volume

NAME                                          READY   STATUS        RESTARTS   AGE
immutable-configmap-volume-5fdb88fcc8-29v8n   1/1     Running       0          13s
immutable-configmap-volume-5fdb88fcc8-52ddd   1/1     Running       0          14s
immutable-configmap-volume-5fdb88fcc8-n5jx4   1/1     Running       0          15s
immutable-configmap-volume-78b6fbff95-5gsfh   1/1     Terminating   0          32m
immutable-configmap-volume-78b6fbff95-7vcj4   1/1     Terminating   0          32m
immutable-configmap-volume-78b6fbff95-vdslm   1/1     Terminating   0          32m

You should eventually see an output similar to:

NAME                                          READY   STATUS    RESTARTS   AGE
immutable-configmap-volume-5fdb88fcc8-29v8n   1/1     Running   0          43s
immutable-configmap-volume-5fdb88fcc8-52ddd   1/1     Running   0          44s
immutable-configmap-volume-5fdb88fcc8-n5jx4   1/1     Running   0          45s

View the logs for a Pod in this Deployment:

# Pick one Pod that belongs to the Deployment, and view its logs
kubectl logs deployment/immutable-configmap-volume

You should see an output similar to the below:

Found 3 pods, using pod/immutable-configmap-volume-5fdb88fcc8-n5jx4
Wed Mar 20 04:24:17 UTC 2024 The name of the company is Fiktivesunternehmen GmbH
Wed Mar 20 04:24:27 UTC 2024 The name of the company is Fiktivesunternehmen GmbH
Wed Mar 20 04:24:37 UTC 2024 The name of the company is Fiktivesunternehmen GmbH

Once all the deployments have migrated to use the new immutable ConfigMap, it is advised to delete the old one.

kubectl delete configmap company-name-20150801

Summary

Changes to a ConfigMap mounted as a Volume on a Pod are available seamlessly after the subsequent kubelet sync.

Changes to a ConfigMap that configures environment variables for a Pod are available after the subsequent rollout for the Pod.

Once a ConfigMap is marked as immutable, it is not possible to revert this change (you cannot make an immutable ConfigMap mutable), and you also cannot make any change to the contents of the data or the binaryData field. You can delete and recreate the ConfigMap, or you can make a new different ConfigMap. When you delete a ConfigMap, running containers and their Pods maintain a mount point to any volume that referenced that existing ConfigMap.

Cleaning up

Terminate the kubectl port-forward commands in case they are running.

Delete the resources created during the tutorial:

kubectl delete deployment configmap-volume configmap-env-var configmap-two-containers configmap-sidecar-container immutable-configmap-volume
kubectl delete service configmap-service configmap-sidecar-service
kubectl delete configmap sport fruits color company-name-20240312

kubectl delete configmap company-name-20150801 # In case it was not handled during the task execution

3 - 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

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:5.0.4
    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.