Don't initialize networks that aren't used by any services.

Signed-off-by: Daniel Nephin <dnephin@docker.com>

compose/cli/main.py

@@ -693,7 +693,7 @@ def run_one_off_container(container_options, project, service, options):
                 start_deps=True,
                 strategy=ConvergenceStrategy.never)
 
-    project.initialize_networks()
+    project.initialize()
 
     container = service.create_container(
         quiet=True,

compose/network.py

@@ -133,12 +133,17 @@ class ProjectNetworks(object):
 
     @classmethod
     def from_services(cls, services, networks, use_networking):
-        networks = {
-            network: networks[network]
+        service_networks = {
+            network: networks.get(network)
             for service in services
             for network in service.get('networks', ['default'])
         }
-        return cls(networks, use_networking)
+        unused = set(networks) - set(service_networks) - {'default'}
+        if unused:
+            log.warn(
+                "Some networks were defined but are not used by any service: "
+                "{}".format(", ".join(unused)))
+        return cls(service_networks, use_networking)
 
     def remove(self):
         if not self.use_networking:

compose/project.py

@@ -351,13 +351,12 @@ class Project(object):
            timeout=DEFAULT_TIMEOUT,
            detached=False):
 
-        services = self.get_services_without_duplicate(service_names, include_deps=start_deps)
+        self.initialize()
+        services = self.get_services_without_duplicate(
+            service_names,
+            include_deps=start_deps)
 
         plans = self._get_convergence_plans(services, strategy)
-
-        self.networks.initialize()
-        self.initialize_volumes()
-
         return [
             container
             for service in services
@@ -369,6 +368,10 @@ class Project(object):
             )
         ]
 
+    def initialize(self):
+        self.networks.initialize()
+        self.initialize_volumes()
+
     def _get_convergence_plans(self, services, strategy):
         plans = {}