Docker for Mac Beta is very nice – more integrated with OS X and significantly faster. The only issue I have encountered so far is the Docker API not being available over HTTP.
The problem can be overcome using socat and launchd; socat is used to expose a HTTP endpoint on which the Docker API is available and launchd to automatically start the socat forwarder each time OS X is started. The socat workaround has been suggested by several persons – thanks! My own laziness drove me to create the launch daemon job.

Install Socat

The most convenient way to install socat is using Homebrew:

• If you haven’t installed Homebrew, do it using the following command in a terminal window:

  /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

• Install socat:

  brew install socat

If you now try the socat command without any parameters in the terminal, you should see output similar to this:

2016/05/21 11:43:41 socat[2598] E exactly 2 addresses required (there are 0); use option "-h" for help

Create a Launch Daemon

Some research told me that creating a launch daemon is the appropriate way to run a script or program at startup. Further details are available here.
After some tinkering, I came up with the following launchd job configuration:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
        <string>se.ivankrizsan.socat_launcher</string>
        <key>Disabled</key>
        <false/>
        <key>RunAtLoad</key>
        <true/>
        <key>KeepAlive</key>
        <true/>
        <key>ProgramArguments</key>
        <array>
            <string>/usr/local/bin/socat</string>
            <string>-d</string>
            <string>TCP-LISTEN:2376,range=127.0.0.1/32,reuseaddr,fork</string>
            <string>UNIX:/var/run/docker.sock</string>
        </array>
        <key>StandardErrorPath</key>
    	<string>/Library/Logs/socat_docker.log</string>
    	<key>StandardOutPath</key>
    	<string>/Library/Logs/socat_docker.log</string>
        <key>StartInterval</key>
       <integer>30</integer>
    </dict>
</plist>

Note that:

• The value of the “Label” key must be unique among your launchd jobs.
• The launchd job can be disabled by setting the key “Disabled” value to true.
• The launchd job will be run at startup (RunAtLoad) and restarted if the process is terminated (KeepAlive).
• The program to execute is the first value in array of the “ProgramArguments” key.
• The arguments to socat needs to have one <string> elements each in the program arguments array.
• The Docker API HTTP endpoint will be made available on port 2376.
  In addition, the Docker API HTTP endpoint will only be available from localhost (range=127.0.0.1/32).
  If you want to open the Docker API HTTP endpoint to access from any IP, modify row 17 of the launchd job configuration to look like this:

  <string>TCP-LISTEN:2376,reuseaddr,fork</string>

• Log from socat will be written to the file /Library/Logs/socat_docker.log
• Socat will be restarted with a 30 second interval if needed (StartInterval).

To activate the launchd job configuration:

• Save the above launchd job configuration to a file with the postfix “.plist” (without quotes).
  My file is named “se.ivankrizsan.socat_launcher.plist”.
• Copy the file you just saved to /Library/LaunchDaemons on your OS X boot disk.
• Open a terminal window.
• Go to the launch daemons directory:

  cd /Library/LaunchDaemons

• Set the owner and group of the new launchd job configuration file:

  sudo chown root:wheel se.ivankrizsan.socat_launcher.plist

• Load the launchd job configuration.
  This can be accomplished either by rebooting OS X or by the following command in the terminal:

  sudo launchctl load se.ivankrizsan.socat_launcher.plist

• Open the Console application and examine the system log for entries related to socat and the socat_docker.log log file.
• Start the Docker (for Mac Beta) application.
• Open the link http://127.0.0.1:2376/version in a browser.
  You should see output similar to this:

  {"Version":"1.11.1","ApiVersion":"1.23","GitCommit":"8b63c77","GoVersion":"go1.5.4","Os":"linux","Arch":"amd64","KernelVersion":"4.4.9-moby","BuildTime":"2016-05-10T10:39:20.341523579+00:00"}

If there are problems regarding the permissions of the launchd job configuration file, use Disk Utility to repair permissions as a last resort.

Happy coding!