Mounting a Kubernetes secret file into an existing directory

config.toml

[thing]
stuff=flibbleAndPtang
foo=bar!@$@

secret-test-pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: secret-test-pod
spec:
  containers:
    - name: test-container
      image: nginx
      volumeMounts:
          - name: secret-volume
            mountPath: /etc/config.toml
            subPath: config.toml
  volumes:
    - name: secret-volume
      secret:
        secretName: secret-test

secret-test.yaml

apiVersion: v1
kind: Secret
metadata:
  name: secret-test
data:
  config.toml: W3RoaW5nXQpzdHVmZj1mbGliYmxlQW5kUHRhbmcKZm9vPWJhciFAJEAK

Note the contents of the secret data.config.toml must be base64 encoded, eg via openssl enc -base64 < config.toml

kubectl apply -f secret-test.yaml
kubectl apply -f secret-test-pod.yaml
kubectl exec secret-test-pod cat /etc/config.toml