Check default socket and localhost:4243 for Docker daemon

fig/cli/command.py

@@ -3,11 +3,13 @@ import logging
 import os
 import re
 import yaml
+import socket
 
 from ..project import Project
 from .docopt_command import DocoptCommand
 from .formatter import Formatter
 from .utils import cached_property
+from .errors import UserError
 
 log = logging.getLogger(__name__)
 
@@ -16,8 +18,26 @@ class Command(DocoptCommand):
     def client(self):
         if os.environ.get('DOCKER_URL'):
             return Client(os.environ['DOCKER_URL'])
-        else:
-            return Client()
+
+        socket_path = '/var/run/docker.sock'
+        tcp_host = '127.0.0.1'
+        tcp_port = 4243
+
+        if os.path.exists(socket_path):
+            return Client('unix://%s' % socket_path)
+
+        try:
+            s = socket.socket()
+            s.connect((tcp_host, tcp_port))
+            s.close()
+            return Client('http://%s:%s' % (tcp_host, tcp_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))
 
     @cached_property
     def project(self):