Ignore invalid host header between go1.6 and old docker clients
50000	     37082 ns/op	  44.50
MB/s	    1920 B/op	      30 allocs/op
50000	     30829 ns/op	  53.52
MB/s	       0 B/op	       0 allocs/op
@@ -849,6 +849,19 @@ set like this:
export DOCKER_TMPDIR=/mnt/disk2/tmp
/usr/local/bin/dockerd -D -g /var/lib/docker -H unix:// > /var/lib/docker-machine/docker.log 2>&1
+Docker clients <= 1.9.2 used an invalid Host header when making request to the
+daemon. Docker 1.12 is built using golang 1.6 which is now checking the validity
+of the Host header and as such clients <= 1.9.2 can't talk anymore to the daemon.
+Docker supports overcoming this issue via a Docker daemon
+environment variable. In case you are seeing this error when contacting the
+daemon:
+
+ Error response from daemon: 400 Bad Request: malformed Host header
+
+The `DOCKER_HTTP_HOST_COMPAT` can be set like this:
+
+ DOCKER_HTTP_HOST_COMPAT=1 /usr/local/bin/dockerd ...
+
## Default cgroup parent
