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ConfigMap

Create Config Map

First create an example property file:

cat <<EOF>/tmp/cm.txt
MYSQL_HOST=mysql.default.cluster.svc
MYSQL_PORT=3306
WEB_ADMIN=false
EXT_URL=https://external.web.local
EOF

kubectl -n default create configmap app-props --from-env-file=/tmp/cm.txt

How is it look like?

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apiVersion: v1
data:
  EXT_URL: https://external.web.local
  MYSQL_HOST: mysql.default.cluster.svc
  MYSQL_PORT: "3306"
  WEB_ADMIN: "false"
kind: ConfigMap
metadata:
  creationTimestamp: "2022-03-29T11:59:18Z"
  name: app-props
  namespace: default
  resourceVersion: "130190991"
  uid: 4170dcea-dc38-43de-aaaa-28b1fd958ed9

Use As System Environments

Entire Configmap

Patch File

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cat <<EOF>/tmp/patch.yaml
spec:
  template:
    spec:
      containers:
        - name: debian-example
          envFrom:
            - configMapRef:
                name: app-props
EOF

Apply

kubectl -n default patch deployment debian-test --patch-file /tmp/patch.yaml

Specify Single Env

You can use only the specific key, value pair.

Patch File

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cat <<EOF>/tmp/patch.yaml
spec:
  template:
    spec:
      containers:
        - name: debian-example
          env:
            - name: EXT_URL_SINGLE
              valueFrom:
                configMapKeyRef:
                  name: app-props
                  key: EXT_URL
EOF

Apply

kubectl -n default patch deployment debian-test --patch-file /tmp/patch.yaml

Use Case: Apache Config

Get The Necessary File

docker run --rm httpd:latest cat /usr/local/apache2/conf/httpd.conf >httpd-custom.conf
docker run --rm httpd:latest cat /usr/local/apache2/conf/mime.types >mime-custom.types

Create Configmap From These Files

kubectl -n default create configmap apache-custom \
--from-file=httpd-custom.conf \
--from-file=mime-custom.types

Attach These Files To The Container

Patch File

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cat <<EOF>/tmp/patch.yaml
spec:
  template:
    spec:
      volumes:
        - name: apache-custom-config
          configMap:
            name: apache-custom
            items:
              - key: httpd-custom.conf
                path: httpd.conf
              - key: mime-custom.types
                path: mime.types
            defaultMode: 420        
      containers:
        - name: httpd
          volumeMounts:
            - name: apache-custom-config
              mountPath: /usr/local/apache2/conf/httpd.conf
              subPath: httpd.conf           
            - name: apache-custom-config
              mountPath: /usr/local/apache2/conf/mime.types 
              subPath: mime.types                         
EOF

Create Sample Deployment

kubectl -n default create deployment httpd-test --image=httpd:latest --replicas=1

Apply The Patch File

kubectl -n default patch deployment httpd-test --patch-file /tmp/patch.yaml

Caution

A container using a ConfigMap as a subPath volume will not receive ConfigMap updates.

Mount Confgimap Into Directory

Patch File

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cat <<EOF>/tmp/patch.yaml
spec:
  template:
    spec:
      volumes:
        - name: apache-custom-config
          configMap:
            name: apache-custom
            defaultMode: 420        
      containers:
        - name: httpd
          volumeMounts:
            - name: apache-custom-config
              mountPath: /sampe-config
EOF

Apply The Patch File

kubectl -n default patch deployment httpd-test --patch-file /tmp/patch.yaml

Warning

This will replace everything inside the original /sampe-config directory.