tl;dr They are going to pick a new pair of things for every major release of Docker. This is meant to let you keep track of more containers over a long time. Apparently you are in fact meant to keep them around if they're still in working order, and remember them "by ID" or by name.
https://github.com/dotcloud/docker/pull/2837
tl;dr They are going to pick a new pair of things for every major release of Docker. This is meant to let you keep track of more containers over a long time. Apparently you are in fact meant to keep them around if they're still in working order, and remember them "by ID" or by name.