Overview of Kubernetes Deployment YAML Configuration

1. apiVersion: apps/v1

• Specifies the API version of Kubernetes to be used for this configuration.
• apps/v1 is the current stable API version for Deployment objects.

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2. kind: Deployment

• Defines the type of Kubernetes object being created.
• A Deployment is used to manage a set of identical Pods, ensuring high availability and scaling.

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3. metadata

Contains metadata (like name and labels) to uniquely identify the deployment.

metadata:

metadata:
  name: notes-service

• name: notes-service
  • Assigns a unique name (notes-service) to this deployment.
  • This name can be used to reference the deployment in other Kubernetes configurations.

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4. spec

Defines the desired state of the deployment.

4.1 replicas

replicas: 1

• Specifies the number of pod instances to be created and maintained.
• Here, 1 means only one replica of the pod will run.
• For high availability, you might set this to a higher number.

4.2 selector

selector:
  matchLabels:
    app: notes-service

• Defines how Kubernetes identifies which pods belong to this deployment.
• The matchLabels key ensures that only pods with the label app: notes-service are managed by this deployment.

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5. template

Defines the pod specification that will be created by this deployment.

5.1 metadata (within template)

metadata:
  labels:
    app: notes-service

• Assigns the label app: notes-service to the pod.
• This must match the selector label in the spec.selector.matchLabels.

5.2 spec (within template)

Defines the specifications for the containers running inside the pod.

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6. Containers

containers:
  - name: notes-service
    image: ram1uj/notes-app-notes-service

• name: notes-service

  • The name of the container inside the pod.
  • Used for logging and referencing within the pod.

• image: ram1uj/notes-app-notes-service

  • Specifies the Docker image to be used for the container.
  • The image ram1uj/notes-app-notes-service is pulled from Docker Hub (or a private registry if configured).
  • The container is created using this image.

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7. Environment Variables

env:
  - name: DB_HOST
    value: mysql
  - name: DB_NAME
    value: notes_db
  - name: DB_USER
    value: root
  - name: DB_PASSWORD
    value: password

• Specifies environment variables for the container.

• These variables can be used by the application inside the container.

• DB_HOST: mysql

  • The database host is set to mysql, meaning the application will connect to a MySQL service.

• DB_NAME: notes_db

  • Specifies the database name as notes_db.

• DB_USER: root

  • Sets the database username as root.

• DB_PASSWORD: password

  • Sets the database password as password (should be managed using Kubernetes Secrets in production).

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8. Ports

ports:
  - containerPort: 8100

• Specifies the container's exposed port.
• 8100 is the port on which the application inside the container will listen.
• Other services or pods can communicate with this application on port 8100.

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9. Image Pull Policy

imagePullPolicy: Always

• Defines when Kubernetes should pull the image.
• Always means Kubernetes will always pull the latest image from the registry whenever the pod is created or restarted.
• This is useful during development but can be changed to IfNotPresent or Never in production for performance reasons.

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Best Practices

1. Use ConfigMaps & Secrets

   • Instead of hardcoding environment variables (like DB_PASSWORD), store them in a ConfigMap or Secret.

2. Increase Replicas for High Availability

   • If you want redundancy, set replicas to a higher value.

3. Use Resource Limits

   • You can specify resource limits (resources.requests and resources.limits) for better control over CPU/memory usage.

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