Attempting to pull a docker image results in an error like the following:
$ docker pull quay.io/coreos/etcd
Pulling repository quay.io/coreos/etcd
Could not reach any registry endpoint
While the error message is extremely cryptic, you are likely attempting to pull a tag that does not exist. If you do not specify a tag, newer versions of docker will attempt to pull the “latest” tag regardless of its existance.