What is Docker?

What Docker is

Docker packages an app and everything it needs into a container that runs the same way on any machine. Containers remove the problem of software working on one computer but not another, and make deployments repeatable.

Docker began as an internal tool at dotCloud, a hosting company led by Solomon Hykes. It was shown to the public and released as open source in 2013. Interest grew so fast that the company renamed itself Docker, Inc. later that year.

Containers existed in Linux before Docker, but Docker made them simple to build, share and run. In 2015 Docker and other companies formed the Open Container Initiative to set shared standards for container images and runtimes. Today those standards are used across the industry, including by Kubernetes and by other container tools.

How Docker works

An app needs more than its own code. It needs the right language version, libraries and system settings. Docker lets you describe all of that in a text file called a Dockerfile. From that file Docker builds an image, which is a read-only package that holds the app and everything it needs.

A container is a running copy of an image. Containers are isolated from each other and from the host, but they share the host's Linux kernel instead of starting a whole operating system. That makes them start in seconds and use less memory than a virtual machine. On Windows and macOS, Docker Desktop runs a small Linux virtual machine behind the scenes to make this work.

Images are stored in a registry such as Docker Hub, so a teammate or a server can pull the same image and run it. Volumes keep data that must survive when a container is removed, and Docker Compose starts several containers together from one file, for example a web app and its database.

Key features of Docker

• Dockerfile builds

  A short text file lists the steps to build your app's image. Anyone can repeat the build and get the same result.

• Images and layers

  Images are built in layers that are cached and reused. Rebuilding after a small change is fast, and shared layers save disk space.

• Docker Hub registry

  A public registry hosts ready-made images for databases, languages and tools. You can also push your own images to share or deploy.

• Docker Compose

  One file describes a set of containers, networks and volumes. A single command starts the whole stack for local development.

• Isolation

  Each container has its own file system, processes and network. Two apps with conflicting requirements can run side by side on one machine.

• Portability

  An image that runs on a laptop runs the same way on a server or cloud host that supports containers.

When to use Docker

Docker compared with alternatives

How to start learning Docker

1. 01Install Docker Desktop on Windows or macOS, or Docker Engine on Linux, using the guides at docs.docker.com.
2. 02Run docker run hello-world in a terminal to confirm that everything works.
3. 03Follow the getting started guide in the official Docker docs to learn images, containers, ports and volumes.
4. 04Write a Dockerfile for a small app you already have and build it with docker build.
5. 05Add a compose.yaml file that starts your app together with a PostgreSQL database.

What Docker costs

Docker Engine and the command line tools are free and open source. Docker Desktop is free for personal use, education and small businesses, and larger companies need a paid subscription. Check the official pricing page for the current terms and plan limits.

How DATAL Projects uses Docker

Docker is part of our backend development work in the Philippines. Common uses:

• Packaging backend services
• Running game servers
• Local development setups

Common questions about Docker