Kubernetes Config Maps
Kubernetes ConfigMaps
ConfigMaps
As seen in the explanation, ConfigMaps hold the configuration data for pods to consume. For example, we could store the color of the Webapp from the previous example, in the form of a ConfigMap.
pradeep@learnk8s$ kubectl explain configmaps
KIND: ConfigMap
VERSION: v1
DESCRIPTION:
ConfigMap holds configuration data for pods to consume.
Before we create any configmaps, let us verify if we have any configmaps already in our cluster.
pradeep@learnk8s$ kubectl get configmaps
NAME DATA AGE
kube-root-ca.crt 1 7h16m
There is one configmap named kube-root-ca.crt already present with one DATA.
To see what is stored in this configmap, we can describe it and look at the Annotations.
pradeep@learnk8s$ kubectl describe configmaps
Name: kube-root-ca.crt
Namespace: default
Labels: <none>
Annotations: kubernetes.io/description:
Contains a CA bundle that can be used to verify the kube-apiserver when using internal endpoints such as the internal service IP or kubern...
Data
====
ca.crt:
----
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
BinaryData
====
Events: <none>
We can create configmaps in multiple different ways. Let us use the help option to see some examples.
pradeep@learnk8s$ kubectl create configmap -h
Create a config map based on a file, directory, or specified literal value.
A single config map may package one or more key/value pairs.
When creating a config map based on a file, the key will default to the basename of the file, and the value will
default to the file content. If the basename is an invalid key, you may specify an alternate key.
When creating a config map based on a directory, each file whose basename is a valid key in the directory will be
packaged into the config map. Any directory entries except regular files are ignored (e.g. subdirectories, symlinks,
devices, pipes, etc).
Aliases:
configmap, cm
Examples:
# Create a new config map named my-config based on folder bar
kubectl create configmap my-config --from-file=path/to/bar
# Create a new config map named my-config with specified keys instead of file basenames on disk
kubectl create configmap my-config --from-file=key1=/path/to/bar/file1.txt --from-file=key2=/path/to/bar/file2.txt
# Create a new config map named my-config with key1=config1 and key2=config2
kubectl create configmap my-config --from-literal=key1=config1 --from-literal=key2=config2
# Create a new config map named my-config from the key=value pairs in the file
kubectl create configmap my-config --from-file=path/to/bar
# Create a new config map named my-config from an env file
kubectl create configmap my-config --from-env-file=path/to/foo.env --from-env-file=path/to/bar.env
<SNIP>
Using this examples, let us create a configmap named webapp-color using --from-literal option to set the color to green.
pradeep@learnk8s$ kubectl create configmap webapp-color --from-literal=APP_COLOR=green
configmap/webapp-color created
pradeep@learnk8s$ kubectl get cm
NAME DATA AGE
kube-root-ca.crt 1 7h26m
webapp-color 1 5s
pradeep@learnk8s$ kubectl describe cm webapp-color
Name: webapp-color
Namespace: default
Labels: <none>
Annotations: <none>
Data
====
APP_COLOR:
----
green
BinaryData
====
Events: <none>
To use this configmap in a Pod definition, we need to make use of -envFrom and -configMapRef options in the Pod Spec.
pradeep@learnk8s$ cat pod-config-map.yaml
apiVersion: v1
kind: Pod
metadata:
name: kodekloud-cm
spec:
containers:
- name: kodekloud-cm
image: kodekloud/webapp-color:v3
envFrom:
- configMapRef:
name: webapp-color
restartPolicy: Never
pradeep@learnk8s$ kubectl create -f pod-config-map.yaml
pod/kodekloud-cm created
pradeep@learnk8s$ kubectl get pods -o wide | grep cm
kodekloud-cm 1/1 Running 0 106s 10.244.0.14 k8s <none> <none>
Verify that app color is changed to green.
pradeep@learnk8s$ minikube ssh -p k8s
_ _
_ _ ( ) ( )
___ ___ (_) ___ (_)| |/') _ _ | |_ __
/' _ ` _ `\| |/' _ `\| || , < ( ) ( )| '_`\ /'__`\
| ( ) ( ) || || ( ) || || |\`\ | (_) || |_) )( ___/
(_) (_) (_)(_)(_) (_)(_)(_) (_)`\___/'(_,__/'`\____)
$ curl 10.244.0.14:8080
<!doctype html>
<title>Hello from Flask</title>
<body style="background: #16a085;"></body>
<div style="color: #e4e4e4;
text-align: center;
height: 90px;
vertical-align: middle;">
<h1>Hello from kodekloud-cm!</h1>
<h2>
Application Version: v3
</h2>
</div>$ curl 10.244.0.14:8080/color
green$
$ exit
logout
If we describe this pod, we can see the following section. Environment Variables from: webapp-color ConfigMap Optional: false
pradeep@learnk8s$ kubectl describe pod kodekloud-cm
Name: kodekloud-cm
Namespace: default
Priority: 0
Node: k8s/192.168.177.29
Start Time: Tue, 15 Feb 2022 20:09:51 +0530
Labels: <none>
Annotations: <none>
Status: Running
IP: 10.244.0.14
IPs:
IP: 10.244.0.14
Containers:
kodekloud-cm:
Container ID: docker://53b0a746b4c95c65bbdce09f416ca6762ec9ce78d2a9618187a86d80465ec349
Image: kodekloud/webapp-color:v3
Image ID: docker-pullable://kodekloud/webapp-color@sha256:3ecd19b1b85db381a0b6f78272458c3c274ac2a38e878d65700393899adb3177
Port: <none>
Host Port: <none>
State: Running
Started: Tue, 15 Feb 2022 20:09:53 +0530
Ready: True
Restart Count: 0
Environment Variables from:
webapp-color ConfigMap Optional: false
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-sq9q4 (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
kube-api-access-sq9q4:
Type: Projected (a volume that contains injected data from multiple sources)
TokenExpirationSeconds: 3607
ConfigMapName: kube-root-ca.crt
ConfigMapOptional: <nil>
DownwardAPI: true
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 10h default-scheduler Successfully assigned default/kodekloud-cm to k8s
Normal Pulled 10h kubelet Container image "kodekloud/webapp-color:v3" already present on machine
Normal Created 10h kubelet Created container kodekloud-cm
Normal Started 10h kubelet Started container kodekloud-cm
Warning NodeNotReady 9h (x2 over 10h) node-controller Node is not ready
