implementation of initial_scale service option (issue #116)

docs/yml.md

@@ -199,3 +199,12 @@ privileged: true
 
 restart: always
 ```
+
+### initial_scale
+
+Specify inital scale for container. Upon service creation or recreation, `initial_scale`
+instances of the service container will be created (and started).
+
+```
+initial_scale: 3
+```

fig/service.py

@@ -93,7 +93,7 @@ def __init__(self, name, client=None, project='default', links=None, volumes_fro
         if 'image' in options and 'build' in options:
             raise ConfigError('Service %s has both an image and build path specified. A service can either be built to image or use an existing image, not both.' % name)
 
-        supported_options = DOCKER_CONFIG_KEYS + ['build', 'expose']
+        supported_options = DOCKER_CONFIG_KEYS + ['build', 'expose', 'initial_scale']
 
         for k in options:
             if k not in supported_options:
@@ -102,6 +102,10 @@ def __init__(self, name, client=None, project='default', links=None, volumes_fro
                     msg += " (did you mean '%s'?)" % DOCKER_CONFIG_HINTS[k]
                 raise ConfigError(msg)
 
+        if options.get('initial_scale', 1) > 1:
+            if not can_be_scaled(options):
+                raise CannotBeScaledError()
+
         self.name = name
         self.client = client
         self.project = project
@@ -164,7 +168,7 @@ def scale(self, desired_num):
         - starts containers until there are at least `desired_num` running
         - removes all stopped containers
         """
-        if not self.can_be_scaled():
+        if not can_be_scaled(self.options):
             raise CannotBeScaledError()
 
         # Create enough containers
@@ -243,13 +247,12 @@ def recreate_containers(self, insecure_registry=False, do_build=True, **override
         """
         containers = self.containers(stopped=True)
         if not containers:
-            log.info("Creating %s..." % self._next_container_name(containers))
-            container = self.create_container(
-                insecure_registry=insecure_registry,
-                do_build=do_build,
-                **override_options)
-            self.start_container(container)
-            return [(None, container)]
+            new_containers = []
+            for _ in range(self.options.get("initial_scale", 1)):
+                log.info("Creating %s..." % self._next_container_name(new_containers))
+                new_container = self.create_container(insecure_registry=insecure_registry, do_build=do_build, **override_options)
+                new_containers.append(new_container)
+            return [(None, self.start_container(nc)) for nc in new_containers]
         else:
             tuples = []
 
@@ -341,13 +344,12 @@ def start_or_create_containers(
         containers = self.containers(stopped=True)
 
         if not containers:
-            log.info("Creating %s..." % self._next_container_name(containers))
-            new_container = self.create_container(
-                insecure_registry=insecure_registry,
-                detach=detach,
-                do_build=do_build,
-            )
-            return [self.start_container(new_container)]
+            new_containers = []
+            for _ in range(self.options.get("initial_scale", 1)):
+                log.info("Creating %s..." % self._next_container_name(new_containers))
+                new_container = self.create_container(insecure_registry=insecure_registry, detach=detach, do_build=do_build)
+                new_containers.append(new_container)
+            return [self.start_container(nc) for nc in new_containers]
         else:
             return [self.start_container_if_stopped(c) for c in containers]
 
@@ -493,12 +495,6 @@ def full_name(self):
         """
         return '%s_%s' % (self.project, self.name)
 
-    def can_be_scaled(self):
-        for port in self.options.get('ports', []):
-            if ':' in str(port):
-                return False
-        return True
-
     def pull(self, insecure_registry=False):
         if 'image' in self.options:
             image_name = self._get_image_name(self.options['image'])
@@ -665,3 +661,10 @@ def env_vars_from_file(filename):
             k, v = split_env(line)
             env[k] = v
     return env
+
+
+def can_be_scaled(options):
+    for port in options.get('ports', []):
+        if ':' in str(port):
+            return False
+    return True

tests/unit/service_test.py

@@ -1,6 +1,7 @@
 from __future__ import unicode_literals
 from __future__ import absolute_import
 import os
+import functools
 
 from .. import unittest
 import mock
@@ -18,6 +19,7 @@
     build_volume_binding,
     APIError,
     parse_repository_tag,
+    CannotBeScaledError,
 )
 
 
@@ -245,6 +247,37 @@ def test_create_container_no_build(self):
         self.assertFalse(self.mock_client.images.called)
         self.assertFalse(self.mock_client.build.called)
 
+    def test_initial_scale_recreate(self):
+        def _side_effect(nd, *args, **kwargs):
+            nd['num'] = num = nd.get('num', 0) + 1
+            return {'Id': 'aabbccdd%d' % num, 'Name': '/default_foo_%d' % num}
+        mock_client = mock.create_autospec(docker.Client)
+        mock_client.create_container.side_effect = functools.partial(_side_effect, {})
+        mock_client.inspect_container.side_effect = functools.partial(_side_effect, {})
+        service = Service('foo', image='redis', client=mock_client, initial_scale=3)
+        ret = service.recreate_containers()
+        self.assertEqual(3, len(ret))
+        for intermediate, new in ret:
+            self.assertIsNone(intermediate)
+            self.assertIsInstance(new, Container)
+
+    def test_initial_scale_start_or_create(self):
+        def _side_effect(nd, *args, **kwargs):
+            nd['num'] = num = nd.get('num', 0) + 1
+            return {'Id': 'aabbccdd%d' % num, 'Name': '/default_foo_%d' % num}
+        mock_client = mock.create_autospec(docker.Client)
+        mock_client.create_container.side_effect = functools.partial(_side_effect, {})
+        mock_client.inspect_container.side_effect = functools.partial(_side_effect, {})
+        service = Service('foo', image='redis', client=mock_client, initial_scale=3)
+        ret = service.start_or_create_containers()
+        self.assertEqual(3, len(ret))
+        for c in ret:
+            self.assertIsInstance(c, Container)
+
+    def test_initial_scale_cannot_be_scaled(self):
+        with self.assertRaises(CannotBeScaledError):
+            service = Service('foo', client=self.mock_client, initial_scale=3, ports=["80:80"])
+
 
 class ServiceVolumesTest(unittest.TestCase):