Try connecting to localdocker:4243

See https://github.com/noplay/docker-osx/pull/22

fig/cli/utils.py

@@ -83,21 +83,29 @@ def docker_url():
         return os.environ['DOCKER_URL']
 
     socket_path = '/var/run/docker.sock'
+    tcp_hosts = [
+        ('localdocker', 4243),
+        ('127.0.0.1', 4243),
+    ]
     tcp_host = '127.0.0.1'
     tcp_port = 4243
 
     if os.path.exists(socket_path):
         return 'unix://%s' % socket_path
 
-    try:
-        s = socket.socket()
-        s.connect((tcp_host, tcp_port))
-        s.close()
-        return 'http://%s:%s' % (tcp_host, tcp_port)
-    except:
-        pass
+    for host, port in tcp_hosts:
+        try:
+            s = socket.create_connection((host, port), timeout=1)
+            s.close()
+            return 'http://%s:%s' % (host, port)
+        except:
+            pass
 
     raise UserError("""
-    Couldn't find Docker daemon - tried %s and %s:%s.
-    If it's running elsewhere, specify a url with DOCKER_URL.
-    """ % (socket_path, tcp_host, tcp_port))
+Couldn't find Docker daemon - tried:
+
+unix://%s
+%s
+
+If it's running elsewhere, specify a url with DOCKER_URL.
+    """ % (socket_path, '\n'.join('tcp://%s:%s' % h for h in tcp_hosts)))