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Docker Roadmap: A Complete Guide 2025

Docker has become one of the most important tools in the world of DevOps. It helps engineers run applications inside containers, which are lightweight and isolated environments. This makes applications run the same way everywhere — whether on your laptop, a testing server, or in production.

In 2025, learning Docker is a must for DevOps engineers. It will help you build faster, avoid errors, and manage applications at scale. In this blog, we’ll go step by step through a simple and practical roadmap to learn Docker.

Why Learn Docker?

1. Speed : Docker containers start in seconds, much faster than traditional virtual machines. This speed allows developers and DevOps engineers to build, test, and deploy applications quickly, making the development cycle more efficient.

2. Portability : Applications inside Docker containers can run anywhere — on a laptop, a testing server, or in the cloud — without changes. This portability removes the “works on my machine” problem and ensures consistent performance.

3. Scalability : Docker makes scaling easy by letting you run multiple containers of the same application. This is ideal for handling high traffic and building microservices-based architectures where each service can grow independently.

4. Career Growth : Docker has become a must-have skill for DevOps engineers. Companies across the globe use Docker in their CI/CD pipelines and cloud platforms. Learning Docker improves your job opportunities, helps you stand out in interviews, and boosts your career growth in DevOps. 

What is Docker?

Docker is an open-source containerization platform that allows you to build, package, and run applications inside lightweight, portable containers.
Think of Docker as a tool that helps you put your application and everything it needs (libraries, dependencies, configuration, OS-level packages) into a single unit called a container.
This ensures that your app will run the same way everywhere – whether on your laptop, a server, or in the cloud.
Difference between containers and virtual machines ? What are Containers?

Containers are lightweight, standalone packages that include everything needed to run an application — code, runtime, libraries, and system tools.

  • They share the host operating system kernel but keep applications isolated from each other.
  • Containers are fast to start, small in size, and very efficient.
  • Example: Running a Node.js app in one container and a MySQL database in another, both on the same system without interfering with each other.
What are Virtual Machines (VMs)? 
Virtual Machines are full computer systems that run on top of a hypervisor (like VMware, VirtualBox, or Hyper-V). Each VM has its own operating system, applications, and resources.
  • VMs are heavier because each one needs a full OS.
  • They take longer to start compared to containers.
  • Example: Running Windows in one VM and Linux in another on the same physical machine.
Road Map for learning Docker


Docker architecture and its components

Docker makes use of a client-server architecture. The Docker client talks with the docker daemon which helps in building, running, and distributing the docker containers. The Docker client runs with the daemon on the same system or we can connect the Docker client with the Docker daemon remotely. With the help of REST API over a UNIX socket or a network, the docker client and daemon interact with each other.

Components of Docker Architecture :
Docker Engine The main part of Docker that runs on your host machine. It provides the platform to build, run, and manage containers.

  • It is made up of three parts: the Docker Daemon, the REST API, and the Docker CLI (Client).
  • Without Docker Engine, containers cannot be created or managed.
Docker Daemon (dockerd)
A background service that does the heavy lifting inside Docker.
  • It listens to requests from the Docker Client and manages Docker objects such as containers, images, networks, and volumes.
  • For example, when you type docker run nginx, the daemon pulls the nginx image (if not available) and starts a container.
  • It can also communicate with other daemons to manage containers across multiple systems.
Docker Client (docker)
The interface through which users interact with Docker.
  • It is usually the command-line tool where you run commands like docker build, docker run, or docker ps.
  • The client talks to the Docker Daemon via REST API.
  • Developers and DevOps engineers mostly work with the client, while the daemon handles the backend processes.
Docker Registries
The storage system where Docker images are stored and shared.
  • Docker Hub is the default public registry, but organizations often use private registries like AWS ECR, Azure ACR, or GCP Artifact Registry.
  • Commands like docker pull fetch images from a registry, and docker push uploads images to one.
  • Registries make it easier for teams to collaborate by sharing standard and custom images.
Containers
The final runnable unit created by Docker.
  • A container is a lightweight, isolated environment that has everything an application needs: code, runtime, system tools, and libraries.
  • Multiple containers can run on the same host, all sharing the host OS kernel, but staying isolated from each other.
  • Containers are fast to start, easy to scale, and perfect for microservices and cloud-native applications.
Important Concepts concept with example which every DevOps engineer must know -
Docker Image
A Docker Image is a read-only template that contains everything needed to run an application—code, libraries, dependencies, and configuration.
Think of it like a recipe: it tells Docker how to create a container, step by step, but the recipe itself doesn’t change.
Docker Hub
Docker Hub is a cloud-based registry where Docker images are stored and shared. It’s the default place developers pull pre-built images from.
Imagine it like GitHub for Docker images—a central library where you can find and reuse what others have built, or upload your own.
Dockerfile
A Dockerfile is a simple text file with instructions to build a Docker Image. It defines the base image, dependencies, and startup commands.
Think of it like a cooking recipe card: it lists the exact steps to prepare a dish (image) so that anyone following it can recreate the same result.
Docker Volumes

Docker volume provide a way to persist data generated by containers, even if the container is stopped or deleted.

It’s like saving your work on a USB drive—no matter how many times you replace your laptop (container), your files (data) are still safe.Docker Compose Docker Compose lets you define and manage multi-container applications using a single YAML file. You can start multiple services (like app + database) with just one command.
Imagine it as a project manager—instead of starting services one by one, it starts them all together in a coordinated way.
Docker in CI/CD 

Using Docker in CI/CD pipelines means applications are built, tested, and deployed inside containers. This ensures consistency across environments. It’s like having a standard box for shipping products—no matter where it goes, the contents remain the same and safe.

Docker Swarm
Docker Swarm is Docker’s native clustering and orchestration tool that helps run containers across multiple machines. It provides scaling and load balancing.
Think of it as a team manager—distributing workloads across many players (nodes) so the job gets done efficiently.

Networking in Docker:

 How containers communicate with each other across different networks (bridge, host, overlay).

  • Bridge Network: The default network that lets containers talk to each other while staying isolated from the outside world.
    Think of it like a private Wi-Fi network for your containers.
  • Host Network: The container shares the host machine’s network directly, without isolation.
    This is like plugging your device directly into the internet without a router in between.

    • Image Commands

    docker image build : Builds an image from a Dockerfile.

    docker image ls : Lists all images.

    docker image rm <image> : Removes an image.

    docker image tag <src> <target> : Tags an image with a new name.

    docker pull <image> : Pulls an image from a registry (e.g., Docker Hub).

    docker push <image> : Pushes an image to a registry.

    docker history <image> : Shows history of an image (layers).

    docker inspect <image> : Displays detailed info about an image.

    Container Commands

    docker run <image> : Runs a new container from an image.

    docker run -d <image> : Runs container in detached mode.

    docker run -it <image> bash : Runs container interactively with shell.

    docker ps : Lists running containers.

    docker ps -a : Lists all containers (running + stopped).

    docker start <container> : Starts a stopped container.

    docker stop <container> : Stops a running container.

    docker restart <container> : Restarts a container.

    docker rm <container> : Removes a stopped container.

    docker kill <container> : Force-stops a running container.

    docker logs <container> : Shows logs of a container.

    docker logs -f <container> : Follows logs (live).

    docker exec -it <container> bash : Executes a command inside container.

    docker top <container> : Displays running processes in a container.

    docker inspect <container> : Displays detailed container information.

    docker cp <container>:/path /host/path : Copies files from container to host.

    Volume Commands

    docker volume ls : Lists all volumes.

    docker volume create <name> : Creates a new volume.

    docker volume inspect <name> : Shows details of a volume.

    docker volume rm <name> : Removes a volume.

    docker run -v <volume>:/path <image> : Mounts a volume to a container.

    Network Commands

    docker network ls : Lists all networks.

    docker network create <name> : Creates a new network.

    docker network inspect <name> : Shows network details.

    docker network rm <name> : Removes a network.

    docker network connect <network> <container> : Connects container to network.

    docker network disconnect <network> <container> : Disconnects container from network.

    Docker Compose Commands

    docker-compose up : Starts all services defined in docker-compose.yml.

    docker-compose up -d : Starts services in detached mode.

    docker-compose down : Stops and removes services, networks, and volumes.

    docker-compose ps : Lists running services.

    docker-compose logs : Shows logs of services.

    docker-compose build : Builds images defined in compose file.

    Cleanup Commands

    docker system prune : Removes all unused containers, networks, and images.

    docker image prune : Removes unused images.

    docker container prune : Removes stopped containers.

    docker volume prune : Removes unused volumes.

    docker system df : Shows disk usage by Docker.

    Docker Swarm Commands

    docker swarm init : Initializes Docker Swarm mode.

    docker swarm join --token <token> : Joins a node to a Swarm.

    docker node ls : Lists swarm nodes.

    docker service create --replicas <n> -p 80:80 <image> : Creates a service.

    docker service ls : Lists services.

    docker service scale <name>=<n> : Scales a service.

    docker stack deploy -c docker-compose.yml <stack> : Deploys a stack.

    Miscellaneous Commands

    docker --version : Shows Docker version.

    docker info : Shows system-wide Docker info.

    docker stats : Displays resource usage of containers.

    docker events : Shows real-time Docker events.

    Tue Aug 26, 2025

    About the Author

    "DevOps is the union of people, processes, and products to enable continuous delivery of value to our end users."     - Donovan Brown

    Ayushman Sen is a DevOps Engineer at CloudDevOpsHub with a passion for cloud technologies and automation. He enjoys writing blogs to share his DevOps knowledge and insights with the community. A true DevOps enthusiast, Ayushman is also passionate about traveling, listening to music, and playing musical instruments.

    Ayushman Sen
    DevOps Engineer at CloudDevOpsHub