Here's a roadmap of Docker and Kubernetes concepts you should cover, along with sample definitions to help guide your learning:

Docker Roadmap

1. Basic Concepts

• Containers: Lightweight, standalone, and executable packages that include everything needed to run a piece of software, including the code, runtime, system tools, and libraries.
• Images: Read-only templates that define how a container should be built, typically created using a Dockerfile.
• Dockerfile: A script that contains a series of instructions used to build a Docker image. For example:

  FROM node:14
  WORKDIR /app
  COPY . .
  RUN npm install
  CMD ["npm", "start"]

• Volumes: Mechanism for persisting data generated by a Docker container outside the container’s lifecycle. Used to share data between containers or with the host.

2. Intermediate Concepts

• Docker Compose: A tool for defining and running multi-container Docker applications using a docker-compose.yml file. For example:

  version: "3"
  services:
    web:
      image: nginx
      ports:
        - "8080:80"
    db:
      image: postgres
      environment:
        POSTGRES_PASSWORD: example

• Networking in Docker: How containers communicate with each other across different networks (bridge, host, overlay).
  • Bridge Network: Default network for containers on a single host to communicate.
  • Host Network: Containers use the host’s networking stack directly.

3. Advanced Concepts

• Docker Swarm: Docker’s built-in orchestration tool for clustering multiple Docker hosts into a single pool, managing containers across multiple nodes.
• Multi-stage Builds: Technique to reduce image size by using multiple FROM instructions in a Dockerfile to create layers.

  FROM golang AS build-env
  WORKDIR /app
  RUN go build -o main .

  FROM alpine
  COPY --from=build-env /app/main /app/main
  CMD ["/app/main"]

4. CI/CD Integration

• Docker in CI/CD: Integrating Docker in CI/CD pipelines to build, test, and deploy containers automatically.

Kubernetes Roadmap

1. Basic Concepts

• Pods: The smallest deployable unit in Kubernetes, usually consisting of one or more containers. All containers in a pod share the same network and storage.
• Deployments: A Kubernetes resource that manages stateless applications, allowing for automated updates and scaling of Pods.

  apiVersion: apps/v1
  kind: Deployment
  metadata:
    name: my-app
  spec:
    replicas: 3
    template:
      spec:
        containers:
          - name: my-container
            image: nginx

• Services: A way to expose a set of Pods to the outside world or other services within the cluster.
  • ClusterIP: Default service type, exposing Pods to internal cluster communication.
  • NodePort: Exposes the service on a static port on each node.
  • LoadBalancer: Integrates with cloud provider load balancers to expose the service externally.

2. Intermediate Concepts

• ConfigMaps and Secrets: Used to manage configuration data and sensitive information (like passwords) separately from the application code.

  • ConfigMap Example:

  apiVersion: v1
  kind: ConfigMap
  metadata:
    name: my-config
  data:
    APP_ENV: production
  

• Persistent Volumes (PVs) and Persistent Volume Claims (PVCs): Mechanisms to manage durable storage that outlives Pod lifecycles.

• Horizontal Pod Autoscaling (HPA): Automatically scales the number of Pods in a deployment or replica set based on CPU/memory usage.

3. Advanced Concepts

• Ingress: Manages external access to services within the cluster, typically HTTP and HTTPS routing.

  apiVersion: networking.k8s.io/v1
  kind: Ingress
  metadata:
    name: example-ingress
  spec:
    rules:
    - host: my-app.example.com
      http:
        paths:
        - path: /
          backend:
            service:
              name: my-service
              port:
                number: 80

• StatefulSets: Similar to deployments but used for managing stateful applications where the identity of Pods matters (e.g., databases).
• Helm: A package manager for Kubernetes, used to define, install, and upgrade applications through Helm charts (pre-configured Kubernetes resources).

4. Kubernetes Networking

• CNI (Container Network Interface): Plugins that allow networking between Pods, enabling Pods to communicate with each other within and across clusters.
• Service Mesh (e.g., Istio or Linkerd): A dedicated infrastructure layer to manage service-to-service communication, offering capabilities like load balancing, security, and observability.

5. Monitoring and Logging

• Prometheus: An open-source monitoring and alerting toolkit used to scrape metrics from Pods.
• Grafana: A tool to visualize data from Prometheus for better cluster monitoring.
• Fluentd/ELK Stack: For log aggregation and visualization within Kubernetes clusters.

6. Security

• RBAC (Role-Based Access Control): Controls access to the Kubernetes API for users and service accounts.
• Pod Security Policies: Policies that restrict the behavior of Pods, e.g., preventing containers from running as root.

Learning Strategy

• Start with Docker: Focus on understanding the core concepts of containerization and practice building, running, and managing containers.
• Move to Kubernetes: Once comfortable with Docker, transition to Kubernetes to learn orchestration, scaling, and managing containerized applications across multiple nodes.

Suggested Learning Path:

1. Learn Docker basics: Containers, images, Dockerfile.
2. Practice deploying a simple multi-container app using Docker Compose.
3. Move to Kubernetes basics: Pods, services, and deployments.
4. Understand networking and volumes in Kubernetes.
5. Dive deeper into advanced orchestration concepts: Autoscaling, Ingress, StatefulSets.
6. Explore CI/CD pipelines with Docker and Kubernetes.

By following this roadmap, you'll cover all the essential concepts needed to work efficiently with Docker and Kubernetes.