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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. Ref: https://kubernetes.io/docs/reference/kubernetes-api/workload-resources/pod-v1/#environment-variables

When defining environment variables in Kubernetes, the order of precedence matters! Here’s how Kubernetes decides which value takes effect when the same variable is defined in multiple places:

1. Explicitly set in the env field (highest priority)

2. Loaded via envFrom (ConfigMaps or Secrets)

   1. If the same key is defined in multiple ConfigMaps or Secrets, the last one takes precedence

3. Defined in the container image (lowest priority)

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containers:
  - name: my-app
    image: my-app-image
    env:
      - name: DB_HOST
        value: "database.internal"  # Highest priority
    envFrom:
      - configMapRef:
          name: my-config
        - secretRef:
            name: my-secret

In the above example, if DB_HOST is defined in both env and envFrom, the value from env will take precedence. If DB_HOST is defined in multiple ConfigMaps or Secrets, the value from the last one will take precedence i.e. my-secret in this case.