MongoDB Deployment

Kubernetes Deployment Overview

• Goal: Deploy two applications — MongoDB and Express — in a Kubernetes cluster.

• Components Used:

  • MongoDB pod with internal access

  • Express deployment with browser access

  • Kubernetes services: internal for MongoDB, external for Express

  • ConfigMap and Secret for configuration and credentials

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Step 1: MongoDB Deployment

MongoDB Pod Setup

• Deployment Configuration:

  • Kind: Deployment

  • Metadata includes:

    • Name: MongoDB-deployment

    • Labels and selectors to match pods

  • Replica Count: 1

  • Container Settings:

    • Image: Latest MongoDB image

    • Container name: MongoDB

    • Port exposed: 27017 (default MongoDB port)

  • Environment Variables:

    • MONGO_INITDB_ROOT_USERNAME: left blank (to be sourced from secret)

    • MONGO_INITDB_ROOT_PASSWORD: left blank (to be sourced from secret)

Secret Creation for Credentials

• File Type: Secret

• Kind: Secret

• Metadata Name: MongoDB-secret

• Type: Opaque (default key-value secret type)

• Data (Base64 encoded):

  • root-username: e.g., username encoded via echo -n username | base64

  • root-password: e.g., password encoded similarly

Referencing Secret in Deployment

• Reference Block:

  • Use valueFrom → secretKeyRef

  • Keys:

    • Username: root-username

    • Password: root-password

  • Ensures no plain-text credentials in config files

  • Improves security by storing sensitive data outside the repo

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Step 2: Internal Service for MongoDB

• Purpose: Allow internal communication between pods.

• Kind: Service

• Name: MongoDB-service

• Selector: Matches deployment labels to connect to MongoDB pod

• Ports:

  • Service port: 27017

  • Target port: 27017 (matches container port)

Validation

• Commands Used:

  • kubectl get service

  • kubectl describe service MongoDB-service

  • Match service endpoint IP with kubectl get pod -o wide output

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Step 3: Express Deployment

Express Pod Setup

• Deployment Configuration:

  • Kind: Deployment

  • Name: Express-deployment

  • Image: mongo-express

  • Container port: 8081 (default port for mongo-express UI)

• Environment Variables Required:

  • ME_CONFIG_MONGODB_ADMINUSERNAME

  • ME_CONFIG_MONGODB_ADMINPASSWORD

  • ME_CONFIG_MONGODB_SERVER

Source of Environment Variables

• Credentials: Referenced from the previously created MongoDB-secret

• MongoDB Server URL: Provided via ConfigMap

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Step 4: ConfigMap for MongoDB URL

• Kind: ConfigMap

• Name: MongoDB-configmap

• Data:

  • Key: database-url

  • Value: MongoDB-service (internal service name of MongoDB)

Referencing in Deployment

• ValueFrom Block:

  • Use configMapKeyRef

  • ConfigMap Name: MongoDB-configmap

  • Key: database-url

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Step 5: External Service for Express

• Purpose: Allow browser-based access to the Express UI.

• Kind: Service

• Name: Express-service

• Type: LoadBalancer (for external exposure)

• Selector: Matches Express pod

• Ports:

  • port: 8081

  • targetPort: 8081

  • nodePort: 30000 (within the required range 30000–32767 for external exposure)

MiniKube Specific Behavior

• External IP shown as "pending" under kubectl get service due to local environment

• Use command minikube service Express-service to:

  • Launch Express UI in browser

  • Display full external URL (IP + NodePort)

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Request Flow Summary

• Incoming Browser Request:

  • Sent to external service (LoadBalancer type)

  • Routed to Express pod

• Express Pod Behavior:

  • Reads database config and credentials from environment variables

  • Connects to MongoDB via internal service

• MongoDB Pod:

  • Authenticates request using credentials from secret

  • Processes request (e.g., create database, display collections)

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Key Notes and Tips

• Order of Resource Creation Matters:

  • Secrets and ConfigMaps must exist before referencing them in deployments

• Best Practices:

  • Avoid hardcoding sensitive info in deployment files

  • Use ConfigMaps and Secrets for clean, secure, modular configurations

  • Use YAML document separator (---) to combine multiple resources in one file

• Validation Commands:

  • kubectl get all filters by component

  • kubectl describe inspects configurations in-depth