Mechanism for Dockerfile customization

This patchset enables potentially full customization of Dockerfiles
provided by Kolla without having to change main Kolla code. Mechanism is
based on jinja2 block mechanism. In our dockerfiles we'll add blocks
(mostly empty) with highly standarized naming, then in override file
users will be able to fill/override contents of these blocks. Example is
shown in this patch.
To enable cutomized override file call build.py

--template-override=path-to-file Only caveat is that header {% extends
.. %} has to stay

Change-Id: I5957024e5652f9677c439fb2fcd524e467b951af
Partially-implements: blueprint third-party-plugin-support

2 files changed, 12 insertions, 3 deletions

diff --git a/kolla/common/config.py b/kolla/common/config.py
index 903fd693d..b1224d09e 100644
--- a/kolla/common/config.py
+++ b/kolla/common/config.py
@@ -142,6 +142,8 @@ _CLI_OPTS = [
                 help=("Don't build images. Generate Dockerfile only")),
     cfg.IntOpt('timeout', default=120,
                help='Time in seconds after which any operation times out'),
+    cfg.StrOpt('template-override',
+               help='Path to template override file'),
 ]
 
 _BASE_OPTS = [
diff --git a/kolla/image/build.py b/kolla/image/build.py
index 40601f0e8..6805ab14c 100755
--- a/kolla/image/build.py
+++ b/kolla/image/build.py
@@ -609,9 +609,6 @@ class KollaWorker(object):
             self.base)
         for path in self.docker_build_paths:
             template_name = "Dockerfile.j2"
-            env = jinja2.Environment(  # nosec: not used to render HTML
-                loader=jinja2.FileSystemLoader(path))
-            template = env.get_template(template_name)
             values = {'base_distro': self.base,
                       'base_image': self.conf.base_image,
                       'base_distro_tag': self.base_tag,
@@ -624,6 +621,16 @@ class KollaWorker(object):
                       'maintainer': self.maintainer,
                       'kolla_version': kolla_version,
                       'rpm_setup': self.rpm_setup}
+            env = jinja2.Environment(  # nosec: not used to render HTML
+                loader=jinja2.FileSystemLoader(path))
+            template = env.get_template(template_name)
+            if self.conf.template_override:
+                template_path = os.path.dirname(self.conf.template_override)
+                template_name = os.path.basename(self.conf.template_override)
+                values['parent_template'] = template
+                env = jinja2.Environment(  # nosec: not used to render HTML
+                    loader=jinja2.FileSystemLoader(template_path))
+                template = env.get_template(template_name)
             if self.include_header:
                 with open(self.include_header, 'r') as f:
                     values['include_header'] = f.read()