Ubuntu 14.04 LTS ships with Docker v0.9.1, as the package docker.io. The launcher script asks for v0.10.x or above, yet Discourse runs fine under the official docker release by Ubuntu.
I would like to think that 14.04.1 provides a vendor upgrade to Docker 1.0, but for now docker.io does not provide specific instructions for upsteam releases on 14.04. A few Docker cloud providers are beginning their Docker deployment on 14.04 hosts with the vendor supported version of Docker.
If we can avoid breaking support for Docker v0.9.1 in the meantime, I see no reason to have the script allow v0.9.1 and up. A solution is to warn the user about upgrading, rather than terminating the script.
I mistakenly posted this under Github issues rather than here. @supermathie commented that as Docker is still new and moving so quickly, encouragement to stay on the latest version is a good thing. @sam mentioned about a possible regression for his reason for not supporting v0.9.1.
Regardless of what version of Docker we decide to support, I’ve improved the logic of the launcher script used by Discourse to support both a minimum, and recommended version. Currently, the launcher script will only run with Docker versions containing 0.10 in their string (so 0.10.0, or 1.0.10, but not 0.11.0)
I am also happy to amend the logic so you can bypass the pre-flight checks. Eg:
./launcher --no-check bootstrap app
This will require quite a few changes internally, but should allow you to simply alias it without needing to fork the launcher script.
I am against supporting 0.9.1 cause you will be in for a shock when your containers stop after upgrading to 0.10, I am fairly confident this will not be fixed with the 0.11 upgrade, the internal design changed in a breaking way.