App Deployment With Kubernetes

DEPLOYING WITH KUBERNETES

Serikiayodele

3 min readFeb 7, 2023

Prerequisites

Minikube
Kubectl

A little intro…

The format for the Kubernetes configuration files is yaml and the configuration basically has 3 parts:

Metadata: where the information of the component exists.
Specification: where the configuration you want to apply to the component is specified, the attributes of the specification will be specific to the kind of component you’re creating.
Status: automatically generated and added by Kubernetes, it gets the status information from the etcd, which is the cluster brain.

In the specification part of the deployment, we have the templates which has it’s own metadata and specification, it’s basically a configuration file inside a configuration file, and this configuration applies to a pod.

Connection is established using labels and selectors, metadata contains the labels and specification contains the selector, the deployment is connected to the pod by telling the deployment to match all the labels with the app value. The deployment label is also used by the service selector which with makes the connection between the service and the deployment or it’s pods.

Service has a port where the service itself is accessible at, the service also needs to know what port to forward the request and on what port that pod is listening and that’s the targetport, this targetport should match the containerport

Prepare Deployment files

Step 1- Mongo

Here are files for the mongo deployment, service and secret.

#mongo.yaml

apiVersion: apps/v1
kind: Deployment
metadata: 
  name: mongodb-deployment
  labels:
    apps: 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

I’ve saved the environmental variables as secrets cause we don’t want everyone having access to those.

# mongo-secret.yaml

apiVersion: v1
kind: Secret
metadata:
    name: mongodb-secret
type: Opaque
data:
    mongo-root-username: <encrypted-username>
    mongo-root-password: <encrypted-password>

Step 2- Mongo-Express

Here are files for the mongo-express deployment, service and config-map.

#mongo-express.yaml

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

---
apiVersion: v1
kind: Service
metadata:
  name: mongo-express-service
spec:
  selector:
    app: mongo-express
  type: LoadBalancer  
  ports:
    - protocol: TCP
      port: 8081
      targetPort: 8081
      nodePort: 30000

ConfigMaps: ConfigMaps are used to store non-sensitive configuration data, such as configuration files, command-line flags, feature toggles, etc. They are stored unencrypted and can be accessed by a pod as environment variables or mounted as files.

# mongo-configmap.yaml

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

Step 3- My-App

Here are files for the app’s deployment and service.

#my-app.yaml

apiVersion: apps/v1
kind: Deployment
metadata: 
  name: my-app-deployment
  labels:
    app: my-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: my-app
  template:
    metadata:
      labels:
        app: my-app
    spec:
      containers:
      - name: my-app
        image: seriki/my-app:1.7
        ports:
        - containerPort: 3000

---
apiVersion: v1
kind: Service
metadata: 
    name: my-app-service
spec:
    selector:
        app: my-app
    ports:
        - protocol: TCP
          port: 3000
          targetPort: 3000

Step 4- Kustomization

I have a kustomization file, which allows you to manage multiple resources as a single unit.

# kustomization.yaml

resources:
- secrets/mongo-secret.yaml
- configmap/mongo-configmap.yaml
- deployments/mongo.yaml
- deployments/mongo-express.yaml
- deployments/my-app.yaml

Now, we just need to run `kubectl apply -k .` from the older holding the kustomization file

And, you should be able to access your app and mongo from their ports.