diff --git a/nodepool/elements/openstack-repos/extra-data.d/50-create-repo-list b/nodepool/elements/openstack-repos/extra-data.d/50-create-repo-list
index 2465d47a09..7a7fd1987d 100755
--- a/nodepool/elements/openstack-repos/extra-data.d/50-create-repo-list
+++ b/nodepool/elements/openstack-repos/extra-data.d/50-create-repo-list
@@ -36,7 +36,7 @@ def get_project_list(url):
         return projects
     except URLError:
         print "Could not open project list url: '%s'" % url
-        return None
+        raise
 
 def main():
     projects = []
diff --git a/tools/build-image.sh b/tools/build-image.sh
index 5f15096ef3..16796adcc3 100755
--- a/tools/build-image.sh
+++ b/tools/build-image.sh
@@ -14,6 +14,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+#
+# Read through this script.  There are a lot of comments that might
+# help you!
+#
+
 # To run on Ubuntu 14.04, this depends on:
 # diskimage-builder
 # qemu-utils
@@ -59,6 +64,21 @@ fi
 ## break into the grub console.  Or set it to 0 for fast boot.
 # export DIB_GRUB_TIMEOUT=10
 
+## The openstack-repos element caches every git repo, wihch can take
+## quite some time.  We can override this, but some minimal repos are
+## required for a successful build.  For speeding up builds when
+## you're testing the following should work, but be very careful
+## stripping things out when generating real images.
+
+## add to /tmp/custom_projects.yaml:
+##
+## - project: openstack-infra/project-config
+## - project: openstack-infra/system-config
+## - project: openstack-dev/devstack
+
+# export DIB_CUSTOM_PROJECTS_LIST_URL='file:///tmp/custom_projects.yaml'
+
+
 # The list of elements here should match nodepool/nodepool.yaml
 disk-image-create -x --no-tmpfs -o $IMAGE_NAME \
     $DISTRO \