kubernetes ConfigMap.md

Config map use case examples

Environment from a ConfigMap

All Environment Variables from ConfigMap

spec:
  containers:
    - name: mycontainer
      envFrom:
        - configMapRef:
            name: myConfigMap

Specific Environment Variables from ConfigMap

spec:
  containers:
    - name: myContainer
      env:
        - name: VAR1
          valueFrom:
            configMapKeyRef:
              name: myConfigMap
              key: VAR1
        - name: VAR2
          valueFrom:
            configMapKeyRef:
              name: myConfigMap
              key: VAR2

Volumes from ConfigMaps

Overlay a directory

Given a config map with multiple keys that are filenames you can

spec:
   containers:
     - name: myContainer
       volumeMounts:
         - name: my-config
           mountPath: /etc/somedir             # absolute target DIRECTORY
   volumes:
     - name: my-config
       configMap:
         name: my-config-map

Mount a single file using a single key from the configMap

spec:
   containers:
     - name: myContainer
       volumeMounts:
         - name: my-config
           mountPath: /etc/somedir/             # absolute target DIRECTORY
   volumes:
     - name: my-config
       configMap:
         name: my-config-map
         items:
           - key: somefile                        # <--- CM key reference
             path: somefile

Note though about example will hide all contents of /etc/somedir despite only injecting a single file.

An alternative is to use subPath as shown below.

Use subPath to replace a single file

spec:
   containers:
     - name: myContainer
       volumeMounts:
         - name: my-config
           mountPath: /etc/somedir/somefile       # absolute target FILE
           subPath: somefile                      # CM <--- key reference
   volumes:
     - name: my-config
       configMap:
         name: my-config-map

Note though the subPath has the disadvantage of not updating with ConfigMap changes.