What is managed?
Docker is a tool that lets you put an app and everything it needs (code, libraries, system tools) into a single, portable package called a container. Think of a container like a sealed box that works the same way on any computer, so the app runs without extra setup.
Let's break it down
- Image: A read‑only template that contains the app’s code and all its dependencies.
- Container: A running instance of an image, isolated from other containers and the host system.
- Docker Engine: The software that creates, runs, and manages containers on your machine.
- Docker Hub: An online library where you can share and download ready‑made images.
Why does it matter?
Containers make development faster and more reliable. You write code once, package it with Docker, and it will run the same way on a laptop, a test server, or in the cloud. This reduces “it works on my machine” problems and speeds up deployment.
Where is it used?
- Building and testing software locally.
- Deploying micro‑services in production (e.g., on Kubernetes).
- Running isolated environments for data science or CI/CD pipelines.
- Packaging legacy applications to run on modern infrastructure.
Good things about it
- Portability: Same container runs everywhere.
- Lightweight: Shares the host OS kernel, so containers start in seconds and use less memory than full virtual machines.
- Consistency: Guarantees the same environment from development to production.
- Ecosystem: Huge library of pre‑built images and tools for orchestration, monitoring, and security.
Not-so-good things
- Security: Containers share the host kernel, so a vulnerability in the kernel can affect all containers.
- Complexity at scale: Managing many containers often requires extra tools like Kubernetes, which have their own learning curve.
- Persistent storage: Storing data long‑term can be trickier because containers are meant to be short‑lived.
- Performance overhead: While lighter than VMs, there is still some overhead compared to running directly on the host OS.