Estimated reading time: 6 minutes

Mar 21, 2019 Premier Developer Consultant Randy Patterson explores how to mix Windows and Linux containers with Docker Compose. Running Linux containers on a Windows host has been available for awhile now. However, getting Windows and Linux containers to communicate without Docker Compose results in using the containers’ IP Addresses. Docker compose is an efficient and easy way of deploying docker containers on a host. Compose takes in a YAML file and creates containers according to its specifications. The specification includes what images are needed to be deployed, which specific ports are needed to be exposed, volumes, cpu and memory usage limits, etc. Oct 18, 2016 When trying to launch a built container with docker-compose up I'm getting an error. ERROR: for app Cannot start service app: invalid header field value 'oci runtime error: containerlinux.go:247: starting container process caused 'exec: 'script/docker-entrypoint.sh ': stat script/docker-entrypoint.sh: no such file or directory ' ' ERROR: compose.cli.main.main: Encountered errors while. Docker-compose version 1.23.2, build 1110ad01; Compose file version 3: Works with 1.13.0 and above; Example: Hosting a Ghost CMS Website. Working with Compose is really straight-forward. You write a yaml file describing your deployment and then run deploy it using the docker-compose cli. Let’s start with a simple Ghost CMS deployment. Overview of Docker Compose. Estimated reading time: 6 minutes. Looking for Compose file reference? Find the latest version here. Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services.

Looking for Compose file reference?Find the latest version here.

Compose is a tool for defining and running multi-container Docker applications.With Compose, you use a YAML file to configure your application’s services.Then, with a single command, you create and start all the servicesfrom your configuration. To learn more about all the features of Compose,see the list of features.

Compose works in all environments: production, staging, development, testing, aswell as CI workflows. You can learn more about each case in Common UseCases.

Using Compose is basically a three-step process:

1. Define your app’s environment with a Dockerfile so it can be reproducedanywhere.

2. Define the services that make up your app in docker-compose.ymlso they can be run together in an isolated environment.

3. Run docker compose up and the Docker compose command starts and runs your entire app. You can alternatively run docker-compose up using the docker-compose binary.

A docker-compose.yml looks like this:

For more information about the Compose file, see theCompose file reference.

Compose has commands for managing the whole lifecycle of your application:

• Start, stop, and rebuild services
• View the status of running services
• Stream the log output of running services
• Run a one-off command on a service

Compose documentation

Features

The features of Compose that make it effective are:

Multiple isolated environments on a single host

Compose uses a project name to isolate environments from each other. You can make use of this project name in several different contexts:

• on a dev host, to create multiple copies of a single environment, such as when you want to run a stable copy for each feature branch of a project
• on a CI server, to keep builds from interfering with each other, you can setthe project name to a unique build number
• on a shared host or dev host, to prevent different projects, which may use thesame service names, from interfering with each other

The default project name is the basename of the project directory. You can seta custom project name by using the-p command line option or theCOMPOSE_PROJECT_NAME environment variable.

The default project directory is the base directory of the Compose file. A custom valuefor it can be defined with the --project-directory command line option.

Preserve volume data when containers are created

Compose preserves all volumes used by your services. When docker-compose upruns, if it finds any containers from previous runs, it copies the volumes fromthe old container to the new container. This process ensures that any datayou’ve created in volumes isn’t lost.

If you use docker-compose on a Windows machine, seeEnvironment variables and adjust the necessary environmentvariables for your specific needs.

Only recreate containers that have changed

Compose caches the configuration used to create a container. When yourestart a service that has not changed, Compose re-uses the existingcontainers. Re-using containers means that you can make changes to yourenvironment very quickly.

Variables and moving a composition between environments

Compose supports variables in the Compose file. You can use these variablesto customize your composition for different environments, or different users.See Variable substitution for moredetails.

You can extend a Compose file using the extends field or by creating multipleCompose files. See extends for more details.

Common use cases

Compose can be used in many different ways. Some common use cases are outlinedbelow.

Development environments

When you’re developing software, the ability to run an application in anisolated environment and interact with it is crucial. The Compose commandline tool can be used to create the environment and interact with it.

The Compose file provides a way to document and configureall of the application’s service dependencies (databases, queues, caches,web service APIs, etc). Using the Compose command line tool you can createand start one or more containers for each dependency with a single command(docker-compose up).

Together, these features provide a convenient way for developers to getstarted on a project. Compose can reduce a multi-page “developer gettingstarted guide” to a single machine readable Compose file and a few commands.

How To Install Docker Compose On Linux Mint

Automated testing environments

An important part of any Continuous Deployment or Continuous Integration processis the automated test suite. Automated end-to-end testing requires anenvironment in which to run tests. Compose provides a convenient way to createand destroy isolated testing environments for your test suite. By defining the full environment in a Compose file, you can create and destroy these environments in just a few commands:

Single host deployments

Compose has traditionally been focused on development and testing workflows,but with each release we’re making progress on more production-oriented features.

Docker Compose On Linux Mint

For details on using production-oriented features, seecompose in production in this documentation.

Release notes

To see a detailed list of changes for past and current releases of DockerCompose, refer to theCHANGELOG.

Getting help

Docker Compose is under active development. If you need help, would like tocontribute, or simply want to talk about the project with like-mindedindividuals, we have a number of open channels for communication.

• To report bugs or file feature requests: use the issue tracker on Github.

• To talk about the project with people in real time: join the#docker-compose channel on the Docker Community Slack.

• To contribute code or documentation changes: submit a pull request on Github.

Estimated reading time: 11 minutes

On this page you build a simple Python web application running on DockerCompose. The application uses the Flask framework and maintains a hit counter inRedis. While the sample uses Python, the concepts demonstrated here should beunderstandable even if you’re not familiar with it.

Prerequisites

Make sure you have already installed both Docker Engineand Docker Compose. You don’t need to install Python or Redis, asboth are provided by Docker images.

Step 1: Setup

Define the application dependencies.

1. Create a directory for the project:

2. Create a file called app.py in your project directory and paste this in:

   In this example, redis is the hostname of the redis container on theapplication’s network. We use the default port for Redis, 6379.

   Handling transient errors

   Note the way the get_hit_count function is written. This basic retryloop lets us attempt our request multiple times if the redis service isnot available. This is useful at startup while the application comesonline, but also makes our application more resilient if the Redisservice needs to be restarted anytime during the app’s lifetime. In acluster, this also helps handling momentary connection drops betweennodes.

3. Create another file called requirements.txt in your project directory andpaste this in:

Step 2: Create a Dockerfile

In this step, you write a Dockerfile that builds a Docker image. The imagecontains all the dependencies the Python application requires, including Pythonitself.

In your project directory, create a file named Dockerfile and paste thefollowing:

This tells Docker to:

• Build an image starting with the Python 3.7 image.
• Set the working directory to /code.
• Set environment variables used by the flask command.
• Install gcc and other dependencies
• Copy requirements.txt and install the Python dependencies.
• Add metadata to the image to describe that the container is listening on port 5000
• Copy the current directory . in the project to the workdir . in the image.
• Set the default command for the container to flask run.

For more information on how to write Dockerfiles, see theDocker user guideand the Dockerfile reference.

Step 3: Define services in a Compose file

Create a file called docker-compose.yml in your project directory and pastethe following:

Docker Compose On Linux

This Compose file defines two services: web and redis.

Web service

The web service uses an image that’s built from the Dockerfile in the current directory.It then binds the container and the host machine to the exposed port, 5000. This example service uses the default port for the Flask web server, 5000.

Redis service

The redis service uses a public Redis image pulled from the Docker Hub registry.

Step 4: Build and run your app with Compose

1. From your project directory, start up your application by running docker-compose up.

   Compose pulls a Redis image, builds an image for your code, and starts theservices you defined. In this case, the code is statically copied into the image at build time.

2. Enter http://localhost:5000/ in a browser to see the application running.

   If you’re using Docker natively on Linux, Docker Desktop for Mac, or Docker Desktop forWindows, then the web app should now be listening on port 5000 on yourDocker daemon host. Point your web browser to http://localhost:5000 tofind the Hello World message. If this doesn’t resolve, you can also tryhttp://127.0.0.1:5000.

   If you’re using Docker Machine on a Mac or Windows, use docker-machine ipMACHINE_VM to get the IP address of your Docker host. Then, openhttp://MACHINE_VM_IP:5000 in a browser.

   You should see a message in your browser saying:

3. Refresh the page.

   The number should increment.

4. Switch to another terminal window, and type docker image ls to list local images.

   Listing images at this point should return redis and web.

   You can inspect images with docker inspect <tag or id>.

5. Stop the application, either by running docker-compose downfrom within your project directory in the second terminal, or byhitting CTRL+C in the original terminal where you started the app.

Step 5: Edit the Compose file to add a bind mount

Edit docker-compose.yml in your project directory to add abind mount for the web service:

The new volumes key mounts the project directory (current directory) on thehost to /code inside the container, allowing you to modify the code on thefly, without having to rebuild the image. The environment key sets theFLASK_ENV environment variable, which tells flask run to run in developmentmode and reload the code on change. This mode should only be used in development.

Step 6: Re-build and run the app with Compose

From your project directory, type docker-compose up to build the app with the updated Compose file, and run it.

Check the Hello World message in a web browser again, and refresh to see thecount increment.

Shared folders, volumes, and bind mounts

• If your project is outside of the Users directory (cd ~), then youneed to share the drive or location of the Dockerfile and volume you are using.If you get runtime errors indicating an application file is not found, a volumemount is denied, or a service cannot start, try enabling file or drive sharing.Volume mounting requires shared drives for projects that live outside ofC:Users (Windows) or /Users (Mac), and is required for any project onDocker Desktop for Windows that uses Linux containers.For more information, see File sharing on Dockerfor Mac, and the general examples on how toManage data in containers.

• If you are using Oracle VirtualBox on an older Windows OS, you might encounter an issue with shared folders as described in this VB troubleticket. Newer Windows systems meet therequirements for Docker Desktop for Windows and do notneed VirtualBox.

Step 7: Update the application

Because the application code is now mounted into the container using a volume,you can make changes to its code and see the changes instantly, without havingto rebuild the image.

Change the greeting in app.py and save it. For example, change the Hello World!message to Hello from Docker!:

Refresh the app in your browser. The greeting should be updated, and thecounter should still be incrementing.

Step 8: Experiment with some other commands

If you want to run your services in the background, you can pass the -d flag(for “detached” mode) to docker-compose up and use docker-compose ps tosee what is currently running:

The docker-compose run command allows you to run one-off commands for yourservices. For example, to see what environment variables are available to theweb service:

See docker-compose --help to see other available commands. You can also install command completion for the bash and zsh shell, which also shows you available commands.

If you started Compose with docker-compose up -d, stopyour services once you’ve finished with them:

You can bring everything down, removing the containers entirely, with the downcommand. Pass --volumes to also remove the data volume used by the Rediscontainer:

At this point, you have seen the basics of how Compose works.

Where to go next

• Next, try the Sample apps with Compose
• To learn more about volumes and bind mounts, see Manage data in Docker