Running a container interactively can be useful, but often it's not what we really need. A web server stack is made up of several components such as the Linux OS, the Apache web server, a PHP runtime, and a database such as MySQL. Collectively, we call this a LAMP stack. If we were to run these in Docker with what we now know, we'd have to keep open several terminal windows!

Obviously that's not what we want to do. Instead, we want to run the containers in the background. That way, we can use them like we would any web server. Fortunately, Docker makes running and managing a container in the background easy with just a few commands.

In this tutorial, we'll:

• Start a container in the background
• Use docker ps to list running Docker containers
• Use docker run to enter a container running in the background
• Use docker kill to stop a container running in the background

Often we don't want to run just one container at a time, but a set of containers that act together to provide a unit of functionality. Yet, docker run only starts one container at a time, with one command in each container at a time.

Docker Compose lets us overcome this limitation by allowing us to define a single file that describes multiple containers, their relationship to each other, and utilities to manage that set of containers as a single unit.

In this tutorial, we'll:

• Introduce Docker Compose
• Run multiple containers at once using Docker Compose
• Identify the purpose of docker-compose.yml
• Learn what resources a set of containers share

Docker Compose allows us to manage several related containers as a single group. We define container sets by creating a creating the Compose file, docker-compose.yml.

In this tutorial, we'll:

• Create the basic structure of the Compose file
• Define a container set using off-the-shelf containers
• Describe where to place it in your project
• See how directory names are significant in Compose

Once we have the docker-compose.yml file created, we can use it to work with a set of containers. Instead of the docker command, Docker Compose has its own command to work with multiple containers at once: docker-compose.

In this tutorial, we'll:

• Cover the basic usage of the Compose command
• Describe how to start, stop, and list running container sets

One of the biggest questions when first learning Docker is "How do we get data into and out of containers?" We can use docker-compose exec to interact with them on the command line, but that doesn't fulfill our needs as developers. Docker provides several mechanisms to share data with the container, each with specific purposes. Docker Compose lets us leverage each of those easily with just a few lines of YAML.

In this tutorial, we'll:

• Identify the various ways we can get data into containers
• Define volumes
• Describe how to use environment variables in Docker
• Describe how to expose network ports from a container set

Bind Volumes are essential to the Drupal developer when using Docker. They allow you to synchronize a directory on your laptop or workstation with a directory in the container. Changes can be replicated in either direction -- from the container to the host OS, or from the host OS to the container. You can add a bind volume to a Compose file with just a single line of code.

In this tutorial, we'll:

• Describe how to use the volumes key in your Compose file
• Best practices for describing mount points
• Introduce different synchronization strategies for volumes and which to use

Docker's goal is to treat containers as reusable, off-the-shelf pieces of infrastructure. Often, however, we need to tailor a container to our specific needs. We may need to enable debugging facilities, enable key configuration options, create databases, and set logins. Many development-oriented containers rely on environment variables to configure containers at runtime.

In this tutorial, we'll:

• Set environment variables using a static value in the Compose file
• Use an environment file to pass multiple variables at once

Network communication is essential when developing for a multi-tier web application like Drupal. Docker automatically isolates each container it runs, only allowing explicit ports to be exposed to the host OS. Docker Compose takes this one step further.

In this tutorial, we'll:

• Explain how Docker isolates containers
• Expose a container's ports to the host OS
• Re-map ports from the container to the host OS

A common task when developing a Drupal site is loading the database into your local development environment. When working with non-Docker local development environments, command line tools or a graphical application are used to load the database dump. These methods also work for Docker with a bit of container configuration. With Docker, you can include all the tooling in containers, reducing the need for utilities on the host OS.

In this tutorial, we'll:

• Outline the challenges for loading a database into a container
• Identify the methods by which a database can be loaded into a container

One of Docker's goals is to make it as simple to deploy and update infrastructure as it is to pull a product off of a shelf. At the center of this goal is Docker Hub, a massive, public, and free-to-use library of Docker images for you to use. As a free service, additional care is required to select images that will provide you with updated, secure, and well-maintained infrastructure.

In this tutorial, we'll:

• Show how Hub is an integral part of using Docker
• Describe registries and private registries
• Identify official images vs. contributed images
• Outline best practices for selecting an image on Hub

When we issue docker run, Docker will attempt to download any images it doesn't have cached locally. Locally cached images take up disk space and are not automatically managed. Furthermore, once downloaded, Docker never updates them for you. You can list, update, or delete locally cached images using the docker command.

In this tutorial, we'll:

• Show how to list all images currently stored on your host OS
• Identify the disk space occupied by cached images
• Learn to explicitly download and update a locally cached image
• Learn to delete images on your system

Often we need a particular version or variation of software in order to support our project. Our site might require Apache Solr 4.x, whereas the same project could be perfectly fine with the latest version of MySQL. Since image names need to be unique on Docker Hub, it'd be inconvenient to require a separate image name for each version of a particular piece of software. Docker solves this problem by using tags.

In this tutorial, we'll:

• Define tags
• Describe how tags are used
• Explain the latest tag
• Show how to find a container's tags on Docker Hub
• Use a tag with docker commands, and in the Compose file

Creating a container set to support Drupal development requires some specialized knowledge. Now that we understand containers, images, how to use Docker Compose (docker-compose), and how to select images on Docker Hub, we're ready to build a container set to support Drupal development.

In this tutorial, we'll:

• Select images of software that we'll need to run Drupal
• Create a new Compose file
• Configure bind volumes and environment variables to support the site
• Test the configuration

See Dockerize an Existing Project if you already have Drupal installed.

One of the primary goals of Docker is to make it as easy to try out and deploy technical infrastructure as it is to pull an item off of a store shelf. But how are these containers built in the first place? A Docker image is built from a Dockerfile, a kind of container source code. The Dockerfile describes how to build and configure a single container.

In this tutorial, we'll:

• Introduce Dockerfiles and see how Docker uses them to build container images
• Outline the general structure of a Dockerfile
• Describe how to build a new image from a Dockerfile

Creating a custom image only requires a Dockerfile with a FROM directive, but since this only renames the image, how do we actually change it? When building a custom image, we often need to add files. Whether they are config files, scripts, compressed archives, or even application binaries, Docker makes it easy to add a file to an image with just one directive.

In this tutorial, we'll:

• Describe how to position files relative to your Dockerfile
• Use the COPY directive to add local files
• Download remote files using the ADD directive

The COPY and ADD directives make it easy to add configuration files or download archives to a container image. While we could install applications into a container using only those directives, it would be difficult and complex. Making matters worse, Docker provides no INSTALL directive. Instead, Docker provides a more general mechanism.

In this tutorial, we'll:

• Introduce the RUN directive and how to run commands during a docker build
• Use package managers to install applications
• Describe best practices for installing software in images

Installation is only one part of setting up a custom Docker image. With few exceptions, we'll want to configure the application to better suit our use case. Docker does not provide a standardized way for applications to be configured. Instead, we rely on the same techniques as we would when configuring the application on a bare-metal server.

In this tutorial, we'll:

• Extract default configuration files from a Docker image
• Give strategies for adding configuration files to the image
• Outline the complexities of using configuration commands in a Dockerfile

The goal of Docker containers is to let you select pieces of technical infrastructure as if you were pulling items off of a shelf. Toward that end, each container image can be configured with a default application to invoke when started with a docker run or as part of a container set with docker-compose up.

In this tutorial, we'll:

• Describe the difference between the build-time and runtime environment of a container
• Use the CMD directive to specify a default command to execute
• Introduce the ENTRYPOINT directive and set a default shell in which to run your CMD

The ENTRYPOINT directive allows us to specify a default shell to use in our custom image, but it can do more than that. Often, we will want to dynamically configure a container on startup by passing it environment variables or using Docker Secrets. By replacing the ENTRYPOINT with a custom script, we can perform this dynamic configuration prior to executing the default application.

In this tutorial, we'll:

• Introduce custom entrypoint scripts
• Describe several strategies for performing dynamic configuration in a container

Often you'll find an image on Docker Hub that almost fits your requirements. For Drupal developers, often the off-the-shelf containers for PHP just aren't enough. Drupal often requires additional PHP extensions such as mbstring or gd. We may also want to use a slightly different configuration, or bake-in a utility like Drush or Drupal Console. Fortunately, Docker makes modifying existing containers easy in a Dockerfile.

In this tutorial, we'll:

• List the reasons why you might modify an existing image
• Describe the general process by which an existing image is modified