app.yaml

# kubectl apply -f app.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: example-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.25.0
        ports:
          - containerPort: 80
        envFrom:
        - secretRef:
            name: example-secret
        volumeMounts:
          - name: config
            mountPath: '/config'
            readOnly: true
      volumes:
        - name: config
          configMap:
            name: example-cm
            items:
              - key: 'file.conf'
                path: 'file.conf'
---
apiVersion: v1
kind: Service
metadata:
  name: example-service
spec:
  selector:
    app.kubernetes.io/name: nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80
---
apiVersion: v1
kind: ConfigMap
metadata:
  name: example-cm
data:
  file.conf: |
    some.key="some-value"
    other.key=42
---
apiVersion: v1
kind: Secret
metadata:
  name: example-secret
data:
  SOME_SECRET: dmVyeS1zZWNyZXQ=