基礎原理:容器技术/Docker/Concepts/container

Explanation

Imagine you're developing a killer web app that has three main components - a React frontend, a Python API, and a PostgreSQL database. If you wanted to work on this project, you'd have to install Node, Python, and PostgreSQL.

How do you make sure you have the same versions as the other developers on your team? Or your CI/CD system? Or what's used in production?

How do you ensure the version of Python (or Node or the database) your app needs isn't affected by what's already on your machine? How do you manage potential conflicts?

Enter containers!

What is a container? Simply put, containers are isolated processes for each of your app's components. Each component - the frontend React app, the Python API engine, and the database - runs in its own isolated environment, completely isolated from everything else on your machine.

Here's what makes them awesome. Containers are:

• Self-contained. Each container has everything it needs to function with no reliance on any pre-installed dependencies on the host machine.
• Isolated. Since containers run in isolation, they have minimal influence on the host and other containers, increasing the security of your applications.
• Independent. Each container is independently managed. Deleting one container won't affect any others.
• Portable. Containers can run anywhere! The container that runs on your development machine will work the same way in a data center or anywhere in the cloud!

Containers versus virtual machines (VMs)

Without getting too deep, a VM is an entire operating system with its own kernel, hardware drivers, programs, and applications. Spinning up a VM only to isolate a single application is a lot of overhead.

A container is simply an isolated process with all of the files it needs to run. If you run multiple containers, they all share the same kernel, allowing you to run more applications on less infrastructure.

Using VMs and containers together Quite often, you will see containers and VMs used together. As an example, in a cloud environment, the provisioned machines are typically VMs. However, instead of provisioning one machine to run one application, a VM with a container runtime can run multiple containerized applications, increasing resource utilization and reducing costs.

Try it out

In this hands-on, you will see how to run a Docker container using the Docker Desktop GUI.