kolla-build: fix build-date LABEL invalidating Docker layer cache

The build-date label was rendered into a LABEL instruction on line
3 of every Dockerfile template, immediately after FROM.

Because Docker invalidates the cache for a changed instruction and
all subsequent layers, a date change caused a full rebuild of every
image on each new calendar day, even when nothing else had changed.

Fix this by removing build-date from the Dockerfile templates and
applying it as a --label argument at build time via image.labels.

Labels passed on the build command line are not part of the
Dockerfile cache key, so the date is still recorded in the image
metadata without affecting layer caching.

Change-Id: I8ef0d85bab1a999a4d09f7cbf0c088ca00fdcf77
Signed-off-by: Michal Nasiadka <mnasiadka@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/docker/cloudkitty/cloudkitty-base/Dockerfile.j2 b/docker/cloudkitty/cloudkitty-base/Dockerfile.j2
index a56370936..b545d4adf 100644
--- a/docker/cloudkitty/cloudkitty-base/Dockerfile.j2
+++ b/docker/cloudkitty/cloudkitty-base/Dockerfile.j2
@@ -1,6 +1,6 @@
 FROM {{ namespace }}/{{ image_prefix }}openstack-base:{{ tag }}
 {% block labels %}
-LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
+LABEL maintainer="{{ maintainer }}" name="{{ image_name }}"
 {% endblock %}
 
 {% block cloudkitty_base_header %}{% endblock %}