Docker is a platform that allows developers to package applications and their dependencies into small containers to streamline the software development process. By containerizing applications, Docker allows seamless version updates to the backend software components without disrupting the functionality of existing systems. This is what makes Docker a game changer in a fast-moving world where speed, efficiency, and consistency of software development are critical. Docker, originally founded as DotCloud, began as an experiment in container technology within an incubator. In 2013, Docker was introduced to the world, and it wasn't long before the giants in the tech industry like Microsoft, IBM, and Red Hat started investing in the platform.
Mastering Docker is crucial for modern software development as it enhances productivity, streamlines workflows, improves scalability, and ensures consistency across environments. It opens up new possibilities in DevOps, cloud computing, and microservices architecture.
However, the first step to understanding Docker begins with learning what containerization in software is.
What are containers?
Containers are lightweight, portable units of software that encapsulate everything an application needs to run efficiently. This includes the necessary libraries, system tools, configuration files, and the application code itself. For instance, an application like WhatsApp can be decomposed into multiple containers, with each container handling a specific function, such as front-end user interfaces, data storage, user authentication, payment processing, and API management.
Why break down applications into containers
The benefits of containerization are extensive, but primarily, it enables applications to be deployed and accessed by multiple users simultaneously without disrupting software updates or deployment processes. Containers provide isolation. Isolating containers in turn ensures that there is increased security. A compromise of one container will not affect another, and there is increased stability even in case of failure/crash of a container, updates, or changes to them. Also, containers are more resource-efficient that VMs. VMs require an entire guest OS, leading to increased memory and storage usage, higher overhead costs, and more time for testing and deployment. Containers, on the other hand, share their host OS, even in isolated environments, combating all the issues stated above. Furthermore, containerization supports DevOps practices and CI/CD pipelines, facilitating faster and more reliable software delivery.
The role of Docker
Containers changed the way software was developed. They provide developers with consistent performance, teams with reduced compatibility issues, and organizations with the freedom to be dynamic and innovative. A pivotal player in this revolution is Docker, Inc. Docker is an open source containerization platform that simplifies the development, transportation, and running of applications by packaging all the necessary code, dependencies, and system tools into containers. These can run consistently across different environments—whether on a developer's machine, on-premise servers, or in the cloud.
What are the different components of Docker?
- Docker Engine: As the name suggests, it is the engine that builds, runs, and manages the containers on Docker. It is the core client-server technology behind Docker. It is comprised of three parts: Daemon (the server part that runs and creates Docker objects like images and containers), the client (which is the command-line interface that interacts with Daemon), and container runtime (container technologies that can maintain container life cycle).
- Docker images: It is the template that contains all the information to run an application like ODE, libraries, tools, and settings. Docker images are built in layers that are stacked on top of one another using a union file system like OverlayFS. An advantage of this is that Docker can reuse layers that are common across different images. For example, if two images use the same base image—like Ubuntu—Docker only stores one copy of that base layer on the disk. This reduces disk space usage and speeds up the build process.
- Docker containers: These are the runtime instances of Docker images that are isolated and contains read-only image layers with an additional thin writable layer on top. This ensures that writing happens only on the top layer, keeping images underneath intact.
- Docker Compose: Compose is to the container as conductor is to the orchestra. Docker Compose is a tool that helps you manage multiple containers at once as a single application. Docker Compose uses a YAML file to define the services, networks, and volumes required for an application.
- Docker Hub: It is an default online registry where you can find all the Docker images shared with others.There are public hubs (accessible to all), private hubs (only for authorized users), image distribution (images shared by developers with code changes) and official images (hosted by hub and maintained by trusted sources)
- Docker registry: While hub is a public registry, organizations can also decide to host their own public or private or self-hosted registry where they can share Docker images.
Key features of Docker
A few key features of Docker that sets it apart are:
- Containerization: Converting applications into containers enhances security, stability, and portability.
- Open source: The platform is continuously evolving and improving because of the constant input and changes by users.
- Scalability: Since Dockers are lightweight, it is easy to scale up or down as per the needs of the organization.
- Productivity: Multiple teams can work on the deployment of the application at once.
- Resource optimization: Each container can use just the amount of resources it needs, reducing overhead.
- Simplified maintenance and updates: You can update one part of the application without affecting the others.
- Faster deployment: Individual services can be developed, tested, and deployed faster, allowing for quicker releases with CI/CD.
Docker vs VMs
A VM is a computing environment that simulates a physical computer. It runs multiple operating systems on one physical machine that can be used to run programs and deploy applications.
| Docker | VMs |
| Shares the OS kernel | Needs one full OS with full virtual hardware |
| Linux friendly | Compatibility with more systems |
| Start up time in seconds | Start up time in minutes |
| Fast and lightweight | Slower and complex |
| Ensures resource optimization | Resource intense |
| Can share files | No options to share |
| Lower costs | Higher overhead costs |
| Better for testing | Better for production |
| Automatic scaling | Manual scaling |
| Better for CI/CD workflows | Better for legacy application |
| Easily portable | Dependent on hypervisor |
| Controllable with commands | Always running |
Docker vs Kubernetes
Kubernetes is an open source orchestration platform that was first developed by Google. Kubernetes is an open source system to deploy, scale, and manage containerized applications anywhere.
Here are a few differences between the two:
| Docker | Kubernetes |
| A platform for building, packaging, and running individual containers | An orchestration tool designed to manage and automate the deployment, scaling, and operation of these containers. |
| Easier to set up and use | More complex and requires better understanding of orchestration concepts |
| Better for simpler applications | Can handle more complex applications |
| Can run containers on multiple hosts, but does not manage them | Specifically designed to manage multiple hosts |
| Apps are deployed as services | Apps are deployed as a combination of pods and services |
| Needs Docker swarm or third party platforms like Kubernetes to replace failed containers and for load balancing | Has self healing and load balancing capabilities |
Benefits of using Docker with Kubernetes
Combining Docker with Kubernetes can help organizations leverage the strengths of both the platforms. Kubernetes can automatically scale, replace failed containers, and manage the life cycle of Docker containers, giving developers more freedom to work on coding rather than infrastructure. Also, Kubernetes can ensure that there is optimum and efficient utilization of containers, maximizing CPU and memory usage. Kubernetes can increase the security of isolated Docker containers by enforcing different policies.
By leveraging the benefits of containerization and orchestration, organizations can achieve greater flexibility, scalability, and efficiency in their development processes.
