Don't use cachefrom if sources don't exist

dockermake/step.py

@@ -94,7 +94,8 @@ def build(self, client, pull=False, usecache=True):
             usecache = False
 
         if not usecache:
-            print('   INFO: Docker caching disabled - forcing rebuild')
+            cprint('  Build cache disabled - this image will be rebuilt from scratch',
+                   'yellow')
 
         dockerfile = u'\n'.join(self.dockerfile_lines)
 
@@ -103,8 +104,8 @@ def build(self, client, pull=False, usecache=True):
                           nocache=not usecache,
                           decode=True, rm=True)
 
-        if usecache and self.cache_from:
-            build_args['cache_from'] = self.cache_from
+        if usecache:
+            utils.set_build_cachefrom(self.cache_from, build_args, client)
 
         if self.build_dir is not None:
             tempdir = self.write_dockerfile(dockerfile)
@@ -150,6 +151,7 @@ def build(self, client, pull=False, usecache=True):
             os.unlink(os.path.join(tempdir, 'Dockerfile'))
             os.rmdir(tempdir)
 
+
     def write_dockerfile(self, dockerfile):
         tempdir = os.path.abspath(os.path.join(self.build_dir, DOCKER_TMPDIR))
         temp_df = os.path.join(tempdir, 'Dockerfile')

dockermake/utils.py

@@ -217,6 +217,7 @@ def get_console_width():
 
 SHOWSIZE = set(('Pushing', 'Pulling', 'Pulled', 'Downloaded', 'Downloading'))
 
+
 def _show_xfer_state(pullstats, item):
     imgid = item['id']
     stat = item['status']
@@ -232,3 +233,20 @@ def _show_xfer_state(pullstats, item):
         return toprint
     else:
         return None
+
+
+def set_build_cachefrom(cache_from, buildargs, client):
+    if cache_from:  # use cachefrom only if at least one of the images exists
+        for image in cache_from:
+            try:
+                client.images.get(image)
+            except docker.errors.ImageNotFound:
+                pass
+            else:
+                cprint("  Build cache sources: %s" % cache_from,
+                       'blue')
+                buildargs['cache_from'] = cache_from
+                return
+        else:
+            cprint("  No build cache sources present; ignoring --cache-repo and --cache-tag",
+                   'blue')

test/test_features.py

@@ -76,8 +76,9 @@ def test_no_cache(twin_simple_targets):
     image1, image2 = twin_simple_targets
     assert image1.id != image2.id
 
-
-def test_explicit_cache_from(twin_simple_targets, docker_client):
+clean8 = creates_images('img1repo/simple-target:img1tag',
+                        'img2repo/simple-target:img2tag')
+def test_explicit_cache_from(twin_simple_targets, docker_client, clean8):
     image1, image2 = twin_simple_targets
     image1.tag('img1repo/simple-target', tag='img1tag')
     image2.tag('img2repo/simple-target', tag='img2tag')
@@ -88,6 +89,15 @@ def test_explicit_cache_from(twin_simple_targets, docker_client):
     assert final_image.id == image1.id
 
 
+def test_cache_fallback(twin_simple_targets, docker_client):
+    image1, image2 = twin_simple_targets
+
+    run_docker_make('-f data/simple.yml simple-target'
+                    ' --cache-repo fakerepo --cache-tag faketag')
+    final_image = docker_client.images.get('simple-target')
+    assert final_image.id == image2.id
+
+
 def _check_files(img, **present):
     for f, record in _FILES.items():
         if not present.get(f, True):