Ubuntu 14.04 does not come with Docker pre-installed by default. There is a Docker "one-click" image available on the "Applications" tab of the create page:

To check if it is installed, you can simply run the command. If you need to do this programmatically, you can check the exit code by running echo $?. If it's installed, you'll see:

$ docker -v
Docker version 1.7.0, build 0baf609
$ echo $?
0

If it's not installed, you'll see:

$ docker -v
The program 'docker' is currently not installed. You can install it by typing:
apt-get install docker
$ echo $?
127

The exit code 0 means that the command was successful, and the code 127 mean "command not found."

We already created a droplet on which we host our site. Can we still create and apply a Docker on this droplet? Basically we want to install PEPS on our system, but needed to install Docker first, any tip on easier way to install Docker on the system?