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Kubernetes: Storage - Use `ConfigMap` as Volume

Kubernetes: Storage - Use ConfigMap as Volume
- Use ConfigMap Volume
- Lab: using configMap volume

Use `ConfigMap Volume`

file permission
- default:
  - rw-r--r-- (0644)
  - rw-r–r– (0644)
files in the configMap volume are symbolic links with permission 0777
edit configMap volume
- the files in the configMap volume are automatically updated.
- It can take up to a minute for the files to be updated
edit configMap env
- can’t be updated while the container is running.
- if container restarts, new config map values will apply to new container
immutable field
- specify whether the CM is mutable.

Example: Using subPath to mount a single file from the volume

spec:
  volumes:
    - name: nginx-config
      configMap:
        name: nginx-config
        optional: true # optional
  containers:
    - name: nginx
      image: nginx
      volumeMounts:
        - name: nginx-config
          mountPath: /usr/share/nginx/html

ConfigMap volumes use symbolic links to provide atomic updates
- Kubernetes ensures that all files in a configMap volume are updated atomically, meaning that all updates are done instantaneously.
- by the use of symbolic file links
the file paths that the application reads point to actual files via two successive symbolic links.

Lab: using `configMap` volume

Create html files

mkdir demo-configmap-volume
cd demo-configmap-volume

# Create index.html
tee index.html<<EOF
<html>
<title>Home</title>
<body>
  <h1> Home </h1>
  <p> This is home page </p>
</body>
</html>
EOF

# Create error.html
tee error.html<<EOF
<html>
<title>Error</title>
<body>
  <h1> Error </h1>
  <p> This is Error page </p>
</body>
</html>
EOF

Error: Create pod without optional

# create pod definition
tee demo-configmap-volume-pod.yaml<<EOF
apiVersion: v1
kind: Pod
metadata:
  name: demo-configmap-volume-pod
spec:
  volumes:
  - name: nginx-config
    configMap:
      name: nginx-config

  containers:
  - name: nginx
    image: nginx
    volumeMounts:
    - name: nginx-config
      mountPath: /usr/share/nginx/html
EOF

Create pod before configMap creation

kubectl apply -f demo-configmap-volume-pod.yaml
# pod/demo-configmap-volume-pod created

kubectl get pod
# NAME                        READY   STATUS              RESTARTS   AGE
# demo-configmap-volume-pod   0/1     ContainerCreating   0          4s

kubectl describe pod demo-configmap-volume-pod
# Events:
#   Type     Reason       Age                From               Message
#   ----     ------       ----               ----               -------
#   Normal   Scheduled    25s                default-scheduler  Successfully assigned default/demo-configmap-volume-pod to docker-desktop
#   Warning  FailedMount  10s (x6 over 25s)  kubelet            MountVolume.SetUp failed for volume "nginx-config" : configmap "nginx-config" not found

Volume is created before pod creation pod creation failed because volume creation caused by configmap not found.

Create pod with optional

# pod definition with optional
tee demo-configmap-volume-pod-optional.yaml<<EOF
apiVersion: v1
kind: Pod
metadata:
  name: demo-configmap-volume-pod-optional
spec:
  volumes:
  - name: nginx-config
    configMap:
      name: nginx-config
      optional: true    # optional
  containers:
  - name: nginx
    image: nginx
    volumeMounts:
    - name: nginx-config
      mountPath: /usr/share/nginx/html
EOF

kubectl apply -f demo-configmap-volume-pod-optional.yaml
# pod/demo-configmap-volume-pod-optional created

kubectl get pod
# NAME                                 READY   STATUS    RESTARTS   AGE
# demo-configmap-volume-pod-optional   1/1     Running   0          8s

# test
kubectl port-forward demo-configmap-volume-pod-optional 8000:80
# Forwarding from 127.0.0.1:8000 -> 80
# Forwarding from [::1]:8000 -> 80

# error: because no home page
curl 127.0.0.1:8000
# <html>
# <head><title>403 Forbidden</title></head>
# <body>
# <center><h1>403 Forbidden</h1></center>
# <hr><center>nginx/1.29.4</center>
# </body>
# </html>

pod created but has no html files

Creating `configMap` Volume

kubectl create cm nginx-config --from-file=index.html --from-file=error.html
# configmap/nginx-config created

kubectl get cm
# NAME               DATA   AGE
# nginx-config       2      9s

kubectl describe cm nginx-config
# Name:         nginx-config
# Namespace:    default
# Labels:       <none>
# Annotations:  <none>

# Data
# ====
# error.html:
# ----
# <html>\r
# <title>Error</title>\r
# <body>\r
#   <h1> Error </h1>\r
#   <p> This is Error page </p>\r
# </body>\r
# </html>

# index.html:
# ----
# <html>\r
# <title>Home</title>\r
# <body>\r
# <h1> Home </h1>\r
# <p> This is home page </p>\r
# </body>\r
# </html>


# BinaryData
# ====

# Events:  <none>

Load All keys

recreate pod

kubectl replace --force -f demo-configmap-volume-pod-optional.yaml
# pod "demo-configmap-volume-pod-optional" deleted from default namespace
# pod/demo-configmap-volume-pod-optional replaced

kubectl port-forward demo-configmap-volume-pod-optional 8000:80
# Forwarding from 127.0.0.1:8000 -> 80
# Forwarding from [::1]:8000 -> 80

curl localhost:8000
# <html>
# <title>Home</title>
# <body>
# <h1> Home </h1>
# <p> This is home page </p>
# </body>
# </html>

curl localhost:8000/error.html
# <html>
# <title>Error</title>
# <body>
#   <h1> Error </h1>
#   <p> This is Error page </p>
# </body>
# </html>

Specify a key

tee demo-configmap-volume-pod-key.yaml<<EOF
apiVersion: v1
kind: Pod
metadata:
  name: demo-configmap-volume-pod-key
spec:
  volumes:
  - name: nginx-config
    configMap:
      name: nginx-config
      optional: true    # optional
      items:
        - key: index.html
          path: index.html
  containers:
  - name: nginx
    image: nginx
    volumeMounts:
    - name: nginx-config
      mountPath: /usr/share/nginx/html
EOF

kubectl apply -f demo-configmap-volume-pod-key.yaml
# pod/demo-configmap-volume-pod-key created

kubectl get pod
# NAME                                 READY   STATUS    RESTARTS   AGE
# demo-configmap-volume-pod-key        1/1     Running   0          7s

kubectl port-forward demo-configmap-volume-pod-key 8080:80
# Forwarding from 127.0.0.1:8080 -> 80
# Forwarding from [::1]:8080 -> 80

# confirm: index pass
curl localhost:8080
# <html>
# <title>Home</title>
# <body>
# <h1> Home </h1>
# <p> This is home page </p>
# </body>
# </html>

# confirm: error not pass
url localhost:8080/error.html
# <html>
# <head><title>404 Not Found</title></head>
# <body>
# <center><h1>404 Not Found</h1></center>
# <hr><center>nginx/1.29.4</center>
# </body>
# </html>

Exlpore file in container

# confirm symbolic link
kubectl exec -it demo-configmap-volume-pod-key -- ls -l /usr/share/nginx/html/index.html
# lrwxrwxrwx 1 root root 17 Dec 27 00:28 /usr/share/nginx/html/index.html -> ..data/index.html

Note_Tech

Kubernetes: Storage - Use ConfigMap as Volume

Use ConfigMap Volume

Lab: using configMap volume

Create html files

Error: Create pod without optional

Create pod with optional

Creating configMap Volume

Load All keys

Specify a key

Kubernetes: Storage - Use `ConfigMap` as Volume

Use `ConfigMap Volume`

Lab: using `configMap` volume

Creating `configMap` Volume