# An introduction to Docker for web developers Docker runs applications. *That’s it.* But by *“application”*, I’m referring to big web dependency stuff… * **web servers** such as Apache and NGINX * **language runtimes** such as Node.js, PHP, Python, Ruby, Rust etc. * **databases** such as MySQL, PostgreSQL, Oracle, MongoDB, redis, etc. * **web applications** such as WordPress, Magento, forums, etc. * and anything else: Elastic Search, message queues, emailers, etc. It doesn’t matter which Operating System you’re using. If your web project has a dependency, it can be downloaded, configured, and launched on Windows, macOS, or Linux in minutes. The following sections provide an overview of Docker features which directly benefit web developers. ### Isolation Docker runs apps in an isolated environment known as a *container*. In essence, you can think of it as a lightweight virtual machine *containing* an OS and the installed/running application. ![Apps running in containers controlled by Docker](https://cdn.hashnode.com/res/hashnode/image/upload/v1660399188922/lxGcEB__K.png) Docker containerized apps Your host OS is not modified or configured in any way. It’s easy to add, remove, or update a container as necessary. This also allows you can run different versions of the same dependency — *even at the same time*. For example, perhaps you require PHP5 for a legacy application but PHP7 for a new project. ### Access A containerized application is still accessed from `localhost`. It normally exposes one or more TCP ports, such as `80` or `443` for a web server or `3306` for MySQL. A MySQL client can attach to `localhost:3306` in the same way as it would for a local installation. Folders on your host PC can be mounted inside a container. You can edit code locally using your existing editor and tools, but have it update and run inside the container. Finally, it’s possible to connect to the container’s shell using SSH to run administrative commands. ### Risk-free Once you have a good set-up, developing with Docker is easier and safer than developing locally. It encourages risk-free experimentation: * you can run older software without being forced to upgrade. PHP3, Python 2, MongoDB 1 — *it doesn’t matter*. * trying a new application or upgrading to the latest version is no longer an issue — you can roll back if there are problems. * creating dangerous code, such as a deletion utility, won’t accidentally wipe your critical OS files! ### Portability Your Docker development environment is portable. It can be stored and reproduced elsewhere, e.g. uploaded to a Git repository and cloned by others on your team. It doesn’t matter what OS they use or whether a dependency is available on their platform. Your web app will work identically. > Docker finally ends those “but it works on my PC” conversations! ### Robustness During development, you will typically run your own web app code in a single container. Optionally, you can run any number of the same app containers on a live server *(Kubernetes and Docker Swarm are designed to do just that)*. Your application will become faster and more robust. Any instance can fail and be restarted while others keep running. You could also update the application with no downtime. ### Docker quick start If Docker is so practical, why do few developers use it? The main reason: *it looks complex*. There are many features, numerous options, and it’s not always clear how to get started. Here’s a quick-start summary to launch the latest version of [MySQL](https://www.mysql.com/) and [Adminer](https://www.adminer.org/), a PHP database client. Install the latest **stable** edition for your OS: * [Docker](https://docs.docker.com/compose/install/) and [Docker Compose](https://docs.docker.com/compose/install/) on Linux * [Docker Desktop for Mac OS Sierra 10.13 and above](https://docs.docker.com/docker-for-mac/install/) * [Docker Desktop for Windows 10](https://docs.docker.com/docker-for-windows/install/) — requires WSL2 (Home or Professional) or Hyper-V (Pro only) > Note that Docker’s command-line interface allows you to start individual containers. Docker Compose can launch multiple containers using a configuration file normally named `docker-compose.yml`. Create a folder with a file named `docker-compose.yml` and add the following content (or [download it directly from Gitub](https://github.com/craigbuckler/docker-web/blob/master/mysql/docker-compose.yml)): version: ‘3’ services: mysql: image: mysql container\_name: mysql environment: - MYSQL\_ROOT\_PASSWORD=mysecret volumes: - mysqldata:/var/lib/mysql ports: - "3306:3306" networks: - mysqlnet restart: on-failure adminer: image: adminer container\_name: adminer depends\_on: - mysql ports: - "8080:8080" networks: - mysqlnet restart: on-failure volumes: mysqldata: networks: mysqlnet: Open a terminal, `cd` to that folder and enter: docker-compose up It will take several minutes to download the container images and initialize the database the first time you run the command. MySQL is ready when you see: mysql | … \[Server\] X Plugin ready for connections. Open `localhost:8080` in your browser to launch Adminer. ![Adminer login screen](https://cdn.hashnode.com/res/hashnode/image/upload/v1660399189992/K5fNvIBdR.png) Enter the login credentials: * Server: **mysql** * Username: **root** * Password: **mysecret** and you can browse, create, edit, or drop databases, tables, users, and other items. You could even create a web application which stores data at `localhost:3306`. To stop the containers, press `Ctrl | Cmd + C` in the terminal or enter docker-compose down in another terminal window. Starting MySQL and Adminer again with `docker-compose up` is almost instantaneous. It’s incredible that you’ve installed, configured, and launched MySQL, PHP, and Adminer with a few minutes effort. ### Next steps > Docker is one of the most useful web development tools you’re not using! [“Docker for Web Developers”](https://dockerwebdev.com/) is a book and video course which will revolutionize your web development workflow. It has one objective: > to quickly demonstrate how you can use Docker in your web development projects. It starts with a concise explanation of Docker terminology and concepts before demonstrating typical projects such as local WordPress, Node.js, and Single-Page App (SPA) environments. You can update source files, execute it instantly, and debug client and server code in Chrome DevTools and VS Code. The examples can be adapted to any technology stack, new projects, or existing apps. See [DockerWebDev.com](https://dockerwebdev.com/) for more information.