Override env values defined in container spec

Question

I have a configmap where I have defined the following key-value mapping in the data section:

apiVersion: v1 kind: ConfigMap metadata:   namespace: test   name: test-config data:   TEST: "CONFIGMAP_VALUE" 

then in the definition of my container (in the deployment / statefulset manifest) I have the following:

        env:         - name: TEST           value: "ANOTHER_VALUE"         envFrom:         - configMapRef:             name: test-config 

When doing this I was expecting that the value from the configmap (TEST="CONFIGMAP_VALUE") will override the (default) value specified in the container spec (TEST="ANOTHER_VALUE"), but this is not the case (TEST always gets the value from the container spec). I couldn't find any relevant documentation about this - is it possible to achieve such env variable value overriding?

Answer 1

From Kubernetes API reference:

envFrom : List of sources to populate environment variables in the container. The keys defined within a source must be a C_IDENTIFIER. All invalid keys will be reported as an event when the container is starting. When a key exists in multiple sources, the value associated with the last source will take precedence. Values defined by an Env with a duplicate key will take precedence. Cannot be updated.

So above clearly states the env will take precedence than envFrom.

When a key exists in multiple sources, the value associated with the last source will take precedence.

So, for overriding, don't use envFrom, but define the value twice within env, see below:

apiVersion: v1 kind: ConfigMap metadata:   namespace: default   name: test-config data:   TEST: "CONFIGMAP_VALUE" --- apiVersion: v1 kind: Pod metadata:   name: busy   namespace: default spec:   containers:   - name: busybox     image: busybox     env:     - name: TEST       value: "DEFAULT_VAULT"     - name: TEST       valueFrom:         configMapKeyRef:           name: test-config           key: TEST     command:     - "sh"     - "-c"     - >       while true; do         echo "$(TEST)";         sleep 3600;       done 

Check:

kubectl logs busy -n default CONFIGMAP_VALUE