Tag built images and use them when starting

A basic measure to get round the fact that adding isn't cached. Once
Docker supports cached adds, this is probably redundant.

plum/service.py

@@ -139,14 +139,20 @@ class Service(object):
             container_options['volumes'] = dict((v.split(':')[1], {}) for v in container_options['volumes'])
 
         if 'build' in self.options:
-            container_options['image'] = self.build()
+            if len(self.client.images(name=self._build_tag_name())) == 0:
+                self.build()
+            container_options['image'] = self._build_tag_name()
 
         return container_options
 
     def build(self):
         log.info('Building %s...' % self.name)
 
-        build_output = self.client.build(self.options['build'], stream=True)
+        build_output = self.client.build(
+            self.options['build'],
+            tag=self._build_tag_name(),
+            stream=True
+        )
 
         image_id = None
 
@@ -162,6 +168,12 @@ class Service(object):
 
         return image_id
 
+    def _build_tag_name(self):
+        """
+        The tag to give to images built for this service.
+        """
+        return '%s_%s' % (self.project, self.name)
+
 
 NAME_RE = re.compile(r'^([^_]+)_([^_]+)_(run_)?(\d+)$')
 

tests/service_test.py

@@ -113,6 +113,18 @@ class ServiceTest(DockerClientTestCase):
         container = service.start()
         container.wait()
         self.assertIn('success', container.logs())
+        self.assertEqual(len(self.client.images(name='default_test')), 1)
+
+    def test_start_container_uses_tagged_image_if_it_exists(self):
+        self.client.build('tests/fixtures/simple-dockerfile', tag='default_test')
+        service = Service(
+            name='test',
+            client=self.client,
+            build='this/does/not/exist/and/will/throw/error',
+        )
+        container = service.start()
+        container.wait()
+        self.assertIn('success', container.logs())
 
     def test_start_container_creates_ports(self):
         service = self.create_service('web', ports=[8000])