Docker / Kubernetes - MongoDB / MongoExpress on Minikube

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MongoDB

mongo-express is a web-based MongoDB admin interface written with Node.js and Express.

Here is a digram that we want to implement with Kubernetes:

We can get the docker images from Dockerhub - mongo / mongo-express.

Git : mongo-mongoexpress-minikube

MongoDB secrets

Secrets (MongoDB username/password) should be in place before we do any MongoDB deployment since MongoDB pods need to access the secrets. So, let's create the secrets with base64 encoded:

$ echo -n 'username' | base64
dXNlcm5hbWU=

$ echo -n 'password' | base64
cGFzc3dvcmQ=

mongodb-secret.yaml:

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

$ kubectl apply -f mongodb-secret.yaml
secret/mongodb-secret created 

$ kubectl get secret
NAME                  TYPE                                  DATA   AGE
default-token-85cdq   kubernetes.io/service-account-token   3      8d
mongodb-secret        Opaque                                2      49s

Now the secrets can be referenced in our deployment.

MongoDB deployment

mongodb-deployment.yaml:

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

$ kubectl apply -f mongodb-deployment.yaml 
deployment.apps/mongodb-deployment created    

$ kubectl get pods
NAME                                 READY   STATUS    RESTARTS   AGE
mongodb-deployment-8b456d6bd-h8phm   1/1     Running   0          2m

MongoDB internal service

We'll append a service to the deployment:

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
spec:
  selector:
    app: mongodb
  ports:
    - protocol: TCP
      port: 27017
      targetPort: 27017

The service is an internal service for communications between the Pods of MongoDB and MongoDB express.

$ kubectl apply -f mongodb-deployment.yaml 
deployment.apps/mongodb-deployment unchanged
service/mongodb-service created

$ kubectl get svc
NAME              TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)     AGE
kubernetes        ClusterIP   10.96.0.1       <none>        443/TCP     8d
mongodb-service   ClusterIP   10.106.245.46   <none>        27017/TCP   100s

$ kubectl describe service mongodb-service 
Name:              mongodb-service
Namespace:         default
Labels:            <none>
Annotations:       Selector:  app=mongodb
Type:              ClusterIP
IP:                10.106.245.46
Port:              <unset>  27017/TCP
TargetPort:        27017/TCP
Endpoints:         172.18.0.8:27017
Session Affinity:  None
Events:            <none>

$ kubectl get pod -o wide
NAME                                 READY   STATUS    RESTARTS   AGE   IP           NODE       NOMINATED NODE   READINESS GATES
mongodb-deployment-8b456d6bd-h8phm   1/1     Running   0          86m   172.18.0.8   minikube   <none>           <none>

$ kubectl get all | grep mongo
pod/mongodb-deployment-8b456d6bd-h8phm   1/1     Running   0          88m
service/mongodb-service   ClusterIP   10.106.245.46   <none>        27017/TCP   10m
deployment.apps/mongodb-deployment   1/1     1            1           88m
replicaset.apps/mongodb-deployment-8b456d6bd   1         1         1       88m

Note that in the service definition, we're not specifying itstype because we're using ClusterIP type of service which is the default service type.

Also note that the Endpoints of the mongodb-service has 172.18.0.8:27017 where the ip is the address of the MongoDB pod with a port 27017.

Mongo express configmap

The same with the secrets, a configmap must already be in our cluster so that our mongo-express can use it as a reference.

mongo-configmap.yaml:

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

Note here the database_url is the same as the mongodb service name, mongodb-service

Create the configmap:

$ kubectl apply -f mongo-configmap.yaml
configmap/mongodb-configmap created

Mongo express deployment

mongo-express-deployment.yaml:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: mongo-express-deployment
  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

Here, the containerPort is the port opened at MongoDB server for monngo-express.

Deploy mongo-express:

$ kubectl apply -f mongo-express-deployment.yaml
deployment.apps/mongo-express-deployment created

$ kubectl get pods
NAME                                        READY   STATUS    RESTARTS   AGE
mongo-express-deployment-864c95f479-b2lrj   1/1     Running   0          2m42s
mongodb-deployment-8b456d6bd-h8phm          1/1     Running   0          171m

$ kubectl logs mongo-express-deployment-864c95f479-b2lrj
Waiting for mongodb-service:27017...
...
Mon Aug 24 23:55:22 UTC 2020 retrying to connect to mongodb-service:27017 (5/5)
Welcome to mongo-express
------------------------


Mongo Express server listening at http://0.0.0.0:8081
Server is open to allow connections from anyone (0.0.0.0)
basicAuth credentials are "admin:pass", it is recommended you change this in your config.js!
Database connected
Admin Database connected

Mongo express external service

We'll add mongo-express service to the deployment:

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

The LoadBalancer assigns a service an external IP address so that it gets external requests.

$ kubectl apply -f mongo-express-deployment.yaml 
deployment.apps/mongo-express-deployment unchanged
service/mongo-express-service created    

$ kubectl get svc
NAME                    TYPE           CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
kubernetes              ClusterIP      10.96.0.1        <none>        443/TCP          8d
mongo-express-service   LoadBalancer   10.101.127.173   <pending>     8081:30000/TCP   4m57s
mongodb-service         ClusterIP      10.106.245.46    <none>        27017/TCP        154m

Unlike the internal service which has a Cluster-IP (internal) by default, the the LoadBalancer service type has additional IP (external). As show in the output, it's currently in <pending>, meaning not assigned yet. This is specific to Minikube, otherwise, it should have one. For example, in environments such as AWS or GCP etc.

So, in Minikube, we can assign external service an IP using minikube service command. With this command, we can access a Service exposed via a node port:

$ minikube service mongo-express-service  
|-----------|-----------------------|-------------|-------------------------|
| NAMESPACE |         NAME          | TARGET PORT |           URL           |
|-----------|-----------------------|-------------|-------------------------|
| default   | mongo-express-service |        8081 | http://172.17.0.2:30000 |
|-----------|-----------------------|-------------|-------------------------|
  Starting tunnel for service mongo-express-service.
|-----------|-----------------------|-------------|------------------------|
| NAMESPACE |         NAME          | TARGET PORT |          URL           |
|-----------|-----------------------|-------------|------------------------|
| default   | mongo-express-service |             | http://127.0.0.1:53752 |
|-----------|-----------------------|-------------|------------------------|
 Opening service default/mongo-express-service in default browser...
 Because you are using a Docker driver on darwin, the terminal needs to be open to run it.   
 
$ minikube ip
127.0.0.1

$ minikube service list
|-------------|-----------------------|--------------|-----|
|  NAMESPACE  |         NAME          | TARGET PORT  | URL |
|-------------|-----------------------|--------------|-----|
| default     | kubernetes            | No node port |
| default     | mongo-express-service |         8081 |     |
| default     | mongodb-service       | No node port |
| kube-system | kube-dns              | No node port |
|-------------|-----------------------|--------------|-----|

The run opens up the following:

Usually, the LoadBalancer service type exposes the service externally using a cloud provider's load balancer. For Minikube, however, a random port is generated and used with node ip, minikube-ip:port.