Docker is a containerization platform that enables developers to package and run applications in isolated environments. Within Docker, there are two important concepts: Docker images and containers.
Docker Image
A Docker image is a non-modifiable template that contains the necessary files and instructions to build a Docker container. Images are created using a Dockerfile, a text file outlining the steps for image construction.
Images are stored in Docker registries, which can be either public or private repositories, accessible based on user permissions.
Docker Container
A Docker container is a runnable instance of a Docker image. Upon creation, a container receives a unique network ID, IP address, and filesystem. Containers utilize the kernel of the host operating system, making them lightweight and efficient.
Containers can be started, stopped, restarted, and scaled based on demand.
Difference between Docker Image and Container
The main difference between a Docker image and a Docker container is that an image is a template, while a container is a running instance of that template.
Here is a table that summarizes the key differences between Docker images and containers:
| Feature | Docker Image | Docker Container |
|---|---|---|
| State | Read-only | Runnable |
| Kernel | Shared with host | Isolated from host |
| Memory | Proportional to size of image | Depends on resources used by application |
| File system | Writable by user | Writable only by root |
| Network | Isolates container from host | Exposes container to host network |
| Ports | Not exposed by default | Exposed to host by default |
Conclusion
Understanding the concepts of Docker images and containers is crucial in leveraging the power of Docker for application building and running. Docker images serve as immutable templates for creating containers, which are ephemeral instances of those images. By grasping the distinctions between images and containers, users can effectively utilize Docker for their development and deployment needs.
Here are some important points to remember regarding Docker images and containers:
- Images are immutable: Once an image is generated, it remains unalterable, ensuring reliability and security.
- Containers are ephemeral: Containers are created and terminated as required, promoting efficiency and scalability.
- Docker images and containers are portable: They can be executed on any Docker-enabled machine.
- Docker images and containers represent a valuable asset for developers, system administrators, and DevOps engineers, facilitating application building, deployment, and runtime operations.