user-data: jinja template to render instance-data.json in cloud-config

Allow users to provide '## template: jinja' as the first line or their
#cloud-config or custom script user-data parts. When this header exists,
the cloud-config or script will be rendered as a jinja template.

All instance metadata keys and values present in
/run/cloud-init/instance-data.json will be available as jinja variables
for the template. This means any cloud-config module or script can
reference any standardized instance data in templates and scripts.

Additionally, any standardized instance-data.json keys scoped below a
'<v#>' key will be promoted as a top-level key for ease of reference in
templates. This means that '{{ local_hostname }}' is the same as using the
latest '{{ v#.local_hostname }}'.

Since instance-data is written to /run/cloud-init/instance-data.json, make
sure it is persisted across reboots when the cached datasource opject is
reloaded.

LP: #1791781

1 files changed, 8 insertions, 3 deletions

diff --git a/cloudinit/handlers/__init__.py b/cloudinit/handlers/__init__.py
index c3576c04..0db75af9 100644
--- a/cloudinit/handlers/__init__.py
+++ b/cloudinit/handlers/__init__.py
@@ -41,7 +41,7 @@ PART_HANDLER_FN_TMPL = 'part-handler-%03d'
 # For parts without filenames
 PART_FN_TPL = 'part-%03d'
 
-# Different file beginnings to there content type
+# Different file beginnings to their content type
 INCLUSION_TYPES_MAP = {
     '#include': 'text/x-include-url',
     '#include-once': 'text/x-include-once-url',
@@ -52,6 +52,7 @@ INCLUSION_TYPES_MAP = {
     '#cloud-boothook': 'text/cloud-boothook',
     '#cloud-config-archive': 'text/cloud-config-archive',
     '#cloud-config-jsonp': 'text/cloud-config-jsonp',
+    '## template: jinja': 'text/jinja2',
 }
 
 # Sorted longest first
@@ -69,9 +70,13 @@ class Handler(object):
     def __repr__(self):
         return "%s: [%s]" % (type_utils.obj_name(self), self.list_types())
 
-    @abc.abstractmethod
     def list_types(self):
-        raise NotImplementedError()
+        # Each subclass must define the supported content prefixes it handles.
+        if not hasattr(self, 'prefixes'):
+            raise NotImplementedError('Missing prefixes subclass attribute')
+        else:
+            return [INCLUSION_TYPES_MAP[prefix]
+                    for prefix in getattr(self, 'prefixes')]
 
     @abc.abstractmethod
     def handle_part(self, *args, **kwargs):