A productive development environment with Docker on OS X

Docker and Boot2Docker are awesome for running containers on OS X, but if you try to use them to do iterative development by mounting a source folder from OS X into your Docker container, you will run into two major problems:

1. Mounted volumes on VirtualBox use vboxsf, which is extremely slow, so compilation and startup times for code in mounted folders is 10-20x slower.
2. File watching is broken since vboxsf does not trigger the inotify file watching mechanism. The only workaround is to enable polling, which is much slower to pick up changes and eats up a lot of resources.

I tried many different solutions (see Alternatives) that didn't work until I finally stumbled across one that does: rsync. With rsync, build and compilation performance in mounted folders is on par with native OS X performance and standard file watching mechanisms work properly too. However, setting it up correctly is a painful process that involves many steps, so to make life easier, I've packaged this process up in this docker-osx-dev project.

For more info, check out the blog post A productive development environment with Docker on OS X.

Status

Beta. A number of developers are successfully using and contributing to docker-osx-dev. It still has some rough edges, but it works well, and makes the docker experience on OS X much better. Give it a try, share your feedback, and submit some pull requests!

Note: this project is inherently a temporary workaround. I hope that in the future, someone will build a better alternative to vboxsf for mounting source code from OS X, and thereby make this entire project obsolete. Until that day comes, I will continue to use the docker-osx-dev scripts to keep myself productive.

Install

Prerequisite: HomeBrew must be installed.

The docker-osx-dev script has an install command that can setup your entire Docker development environment on OS X, including installing Docker and Boot2Docker:

curl -o /usr/local/bin/docker-osx-dev https://raw.githubusercontent.com/brikis98/docker-osx-dev/master/src/docker-osx-dev
chmod +x /usr/local/bin/docker-osx-dev
docker-osx-dev install

Three notes about the install command:

1. It is idempotent, so if you have some of the dependencies installed already, it will not overwrite them.
2. When the install completes, it prints out instructions for one source command you have to run to pick up important environment variables in your current shell, so make sure not to skip that step!
3. Once the install completes, you can use the docker-osx-dev script to sync files, as described in the next section.

Usage

The install command will install, configure, and run Boot2Docker on your system, so the only thing left to do is to run the docker-osx-dev script and tell it what folders to sync. If you run it with no arguments, it will sync the current folder to the Boot2Docker VM:

> cd /foo/bar
> docker-osx-dev
[INFO] Performing initial sync of paths: /foo/bar
[INFO] Watching: /foo/bar

Alternatively, you can use the -s flag to specify what folders to sync (run docker-osx-dev -h to see all supported options):

> docker-osx-dev -s /foo/bar
[INFO] Performing initial sync of paths: /foo/bar
[INFO] Watching: /foo/bar

Now, in a separate tab, you can run a Docker container and mount the current folder in it using the -v parameter. For example, here is how you can fire up the tiny Alpine Linux image and get a Linux console in seconds:

> cd /foo/bar
> docker run -v $(pwd):/src -it --rm gliderlabs/alpine:3.1 sh
/ # cd /src
/ # echo "I'm in a $(uname) container and my OS X files are being synced to $(pwd)!"
I'm in a Linux container and my OS X files are being synced to /src!

As you make changes to the files in the /foo/bar folder on OS X, using the text editors, IDEs, and tools you're used to, they will be automatically synced to the /src folder in the Docker image. Moreover, file watchers should work normally in the Docker container for any framework that supports hot reload (e.g. Grunt, SBT, Jekyll) without any need for polling, so you should be able to follow a "make a change and refresh the page" development model.

If you are using Docker Compose, docker-osx-dev will automatically sync any folders marked as volumes in docker-compose.yml. For example, let's say you had the following docker-compose.yml file:

web:  
  image: training/webapp
  volumes:
    - /foo:/src
  ports:
    - "5000:5000"
db:
  image: postgres    

First, run docker-osx-dev:

> docker-osx-dev
[INFO] Using sync paths from Docker Compose file at docker-compose.yml
[INFO] Performing initial sync of paths: /foo
[INFO] Watching: /foo

Notice how it automatically found /foo in the docker-compose.yml file. Now you can start your Docker containers:

docker-compose up

This will fire up a Postgres database and the training webapp (a simple "Hello, World" Python app), mount the /foo folder into /src in the webapp container, and expose port 5000. You can now test this webapp by going to:

http://dockerhost:5000

When you install docker-osx-dev, it adds an entry to your /etc/hosts file so that http://dockerhost works as a URL for testing your Docker containers.

docker-machine support

docker-machine support is experimental. You can use it as the way it is used for boot2docker, but run docker-machine env before. So as an example, run as:

> docker-machine create --driver virtualbox <machine-name>
> eval "$(docker-machine env <machine-name>)"
> docker-osx-dev install
> cd /foo/bar
> docker-osx-dev
[INFO] Performing initial sync of paths: /foo/bar
[INFO] Watching: /foo/bar

In this case, docker-osx-dev will use the machine defined in the DOCKER_MACHINE_NAME env var, defined by docker-machine env. Alternatively, use the --machine-name <machine-name> argument.

Note: when running docker-osx-dev for boot2docker, please make sure the env var DOCKER_MACHINE_NAME is not defined.

How it works

The install command installs all the software you need:

1. Docker
2. Boot2Docker
3. Docker Compose
4. VirtualBox
5. fswatch
6. The docker-osx-dev script which you can use to start/stop file syncing

The install command also:

1. Adds the Docker environment variables to your environment file (e.g. ~/.bash_profile) so it is available at startup.
2. Adds an entry to /etc/hosts so that http://dockerhost works as a valid URL for your docker container for easy testing.

Instead of using VirtualBox shared folders and vboxsf, docker-osx-dev keeps files in sync by using fswatch to watch for changes and rsync to quickly sync the files to the Boot2Docker VM. By default, the current source folder (i.e. the one you're in when you run docker-osx-dev) is synced. If you use docker-compose, docker-osx-dev will sync any folders marked as volumes. Run docker-osx-dev -h to see all the other options supported.

Limitations and known issues

File syncing is currently one way only. That is, changes you make on OS X will be visible very quickly in the Docker container. However, changes in the Docker container will not be propagated back to OS X. This isn't a problem for most development scenarios, but time permitting, I'll be looking into using Unison to support two-way sync. The biggest limitation at the moment is getting a build of Unison that will run on the Boot2Docker VM.

Contributing

Contributions are very welcome via pull request. This project is in a very early alpha stage and it needs a lot of work. Take a look at the issues for known bugs and enhancements, especially the ones marked with the help wanted tag.

Running the code locally

To run the local version of the code, just clone the repo and run your local copy of docker-osx-dev:

> git clone https://github.com/brikis98/docker-osx-dev.git
> cd docker-osx-dev
> ./src/docker-osx-dev

Running unit tests

To run the unit tests, install bats (brew install bats) and run the corresponding files in the test folder:

> ./test/docker-osx-dev.bats 
 ✓ index_of doesn't find match in empty array
 ✓ index_of finds match in 1 item array
 ✓ index_of doesn't find match in 1 item array
 ✓ index_of finds match in 3 item array

[...]

51 tests, 0 failures

Running integration tests

I started to create integration tests for this project in test/integration-test.sh, but I hit a wall. The point of the integration test would be to run Boot2Docker in a VM, but most CI providers (e.g. TravisCI and CircleCI) already run your build in their own VM, so this would require running a VM-in-a-VM. As described in #7, I can't find any way to make this work. If anyone has any ideas, please take a look!

Alternatives

Below are some of the other solutions I tried to make Docker productive on OS X (I even created a StackOverflow Discussion to find out what other people were doing.) With most of them, file syncing was still too slow to be usable, but they were useful to me to learn more about the Docker ecosystem, and perhaps they will be useful for you if docker-osx-dev doesn't work out:

1. boot2docker-vagrant: Docker, Vagrant, and the ability to choose between NFS, Samba, rsync, and vboxsf for file syncing. A lot of the work in this project inspired docker-osx-dev.
2. dinghy: Docker + Vagrant + NFS. I found NFS was 2-3x slower than running builds locally, which was much faster than the 10-20x slowness of vboxsf, but still too slow to be usable.
3. docker-unison: Docker + Unison. The Unison File Synchronizer should be almost as fast as rsync, but I ran into strange connection errors when I tried to use it with Docker.
4. Polling in Jekyll and Polling in SBT/Play. Some of the file syncing solutions, such as vboxsf and NFS, don't work correctly with file watchers that rely on inotify, so these are a couple examples of how to switch from file watching to polling. Unfortunately, this eats up a fair amount of resources and responds to file changes slower, especially as the project gets larger.
5. Hodor. Uses the Unison File Synchronizer to sync files. I have not had a chance to try this project out yet.

License

This code is released under the MIT License. See LICENSE.txt.

Changelog

• 06/05/15: merged the setup.sh and docker-osx-dev scripts together since they share a lot of the same code and bash scripts don't have any easy ways to define modules, download dependencies, etc.
• 05/25/15: Second version released. Removes Vagrant dependency and uses just rsync + Boot2Docker. If you had installed the first version, you should delete your Vagrantfile, delete the old version of /usr/local/bin/docker-osx-dev, and re-run the setup.sh script.
• 05/19/15: Initial version released. Uses Vagrant + rsync + Boot2Docker.