k8s pod failed to connect mongodb

Question

I'm trying to do a k8s tutorial on youtube https://www.youtube.com/watch?v=X48VuDVv0do&t=5428s. An error occured that k8s pod failed to connect mongodb when I create the deployment mongo-express. Please kindly help!

Error Info of pod retrieved by kubectl logs command:

Welcome to mongo-express
------------------------


(node:7) [MONGODB DRIVER] Warning: Current Server Discovery and Monitoring engine is deprecated, and will be removed in a future version. To use the new Server Discover and Monitoring engine, pass option { useUnifiedTopology: true } to the MongoClient constructor.
Could not connect to database using connectionString: mongodb://username:password@mongodb-service:27017/"
(node:7) UnhandledPromiseRejectionWarning: MongoNetworkError: failed to connect to server [mongodb-service:27017] on first connect [Error: getaddrinfo ENOTFOUND mongodb-service
    at GetAddrInfoReqWrap.onlookup [as oncomplete] (dns.js:66:26) {
  name: 'MongoNetworkError'
}]
    at Pool.<anonymous> (/node_modules/mongodb/lib/core/topologies/server.js:441:11)
    at Pool.emit (events.js:314:20)
    at /node_modules/mongodb/lib/core/connection/pool.js:564:14
    at /node_modules/mongodb/lib/core/connection/pool.js:1000:11
    at /node_modules/mongodb/lib/core/connection/connect.js:32:7
    at callback (/node_modules/mongodb/lib/core/connection/connect.js:300:5)
    at Socket.<anonymous> (/node_modules/mongodb/lib/core/connection/connect.js:330:7)
    at Object.onceWrapper (events.js:421:26)
    at Socket.emit (events.js:314:20)
    at emitErrorNT (internal/streams/destroy.js:92:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:60:3)
    at processTicksAndRejections (internal/process/task_queues.js:84:21)
(node:7) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:7) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

configuration files Configuration files of kubernetes component for your reference.

 1. kubernetes secret 
apiVersion: v1
kind: Secret
metadata:
        name: mongodb-secret
type: Opaque
data:
        mongo-root-username: dXNlcm5hbWU=
        mongo-root-password: cGFzc3dvcmQ=```


2. mongodb deployment & service
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongodb-deployment
  labels:
    app: mongodb
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongodb
  template:
    metadata:
      labels:
        app: mongodb
    spec:
      containers:
        - name: mongodb
          image: mongo
          ports:
            - containerPort: 27017
          env:
            - name: MONGO_INITDB_ROOT_USERNAME
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-username
            - name: MONGO_INITDB_ROOT_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-password
---
apiVersion: v1
kind: Service
metadata:
  name: mongo-service
spec:
  selector:
    app: mongodb
  ports:
    - protocol: TCP
      port: 27017
      targetPort: 27017```

 3. kubernetes configmap
```apiVersion: v1
kind: ConfigMap
metadata:
  name: mongodb-configmap
data:
  database_url: mongodb-service```
 4. mongo-express
```apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo-express
  labels:
    app: mongo-express
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongo-express
  template:
    metadata:
      labels:
        app: mongo-express
    spec:
      containers:
        - name: mongo-express
          image: mongo-express
          ports:
            - containerPort: 8081
          env:
            - name: ME_CONFIG_MONGODB_ADMINUSERNAME
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-username
            - name: ME_CONFIG_MONGODB_ADMINPASSWORD
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-password
            - name: ME_CONFIG_MONGODB_SERVER
              valueFrom:
                configMapKeyRef:
                  name: mongodb-configmap
                  key: database_url

Answer 1

I followed the same tutorial and faced the same issue. The problem is with docker. Starting minikube with docker was the issue, seems like docker has some limitations. Install hyperkit if you are using MacOS, Hyper-V if Windows or install virtualbox if you are using some distribution of linux.

Then start minikube with the virtual machine you installed, like this

minikube start --driver=virtualbox

Answer 2

The ConfigMap references a service that does not exist. If in 2. mongodb deployment & service, in your service section, you change your metadata name to name: mongodb-service, everything should work just fine. See the files below:

mongo-secret.yml

apiVersion: v1
kind: Secret
metadata:
  name: mongodb-secret
type: Opaque
data:
  mongo-root-username: dXNlcm5hbWU=
  mongo-root-password: cGFzc3dvcmQ=

mongo-configmap.yml

apiVersion: v1
kind: ConfigMap
metadata:
  name: mongodb-configmap
data:
  database_url: mongodb-service

mongodb.yml <= THIS FILE CHANGED

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongodb-deployment
  labels:
    app: mongodb
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongodb
  template:
    metadata:
      labels:
        app: mongodb
    spec:
      containers:
        - name: mongodb
          image: mongo
          ports:
            - containerPort: 27017
          env:
            - name: MONGO_INITDB_ROOT_USERNAME
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-username
            - name: MONGO_INITDB_ROOT_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-password
---
apiVersion: v1
kind: Service
metadata:
  name: mongodb-service # <= THIS HAS CHANGED
spec:
  selector:
    app: mongodb
  ports:
    - protocol: TCP
      port: 27017
      targetPort: 27017

mongo-express.yml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo-express
  labels:
    app: mongo-express
spec:
  replicas: 1
  selector:
    matchLabels:
      app: mongo-express
  template:
    metadata:
      labels:
        app: mongo-express
    spec:
      containers:
        - name: mongo-express
          image: mongo-express
          ports:
            - containerPort: 8081
          env:
            - name: ME_CONFIG_MONGODB_ADMINUSERNAME
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-username
            - name: ME_CONFIG_MONGODB_ADMINPASSWORD
              valueFrom:
                secretKeyRef:
                  name: mongodb-secret
                  key: mongo-root-password
            - name: ME_CONFIG_MONGODB_SERVER
              valueFrom:
                configMapKeyRef:
                  name: mongodb-configmap
                  key: database_url

To test, make sure you run the secret and the configmap first:

$ kubectl apply -f mongo-secret.yml
$ kubectl apply -f mongo-configmap.yml
$ kubectl apply -f mongodb.yml
$ kubectl apply -f mongo-express.yml

Lastly, if you want to make sure the app works, you can add this service to your mongo-express.yml file:

---
apiVersion: v1
kind: Service
metadata:
  name: mongo-express-service
spec:
  selector:
    app: mongo-express
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 8081
      targetPort: 8081

Now in your terminal run minikube tunnel and in your browser visit localhost:8081.

Good luck!