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, 90 insertions, 0 deletions

diff --git a/cloudinit/cmd/devel/render.py b/cloudinit/cmd/devel/render.py
new file mode 100755
index 00000000..e85933db
--- /dev/null
+++ b/cloudinit/cmd/devel/render.py
@@ -0,0 +1,90 @@
+# This file is part of cloud-init. See LICENSE file for license information.
+
+"""Debug jinja template rendering of user-data."""
+
+import argparse
+import os
+import sys
+
+from cloudinit.handlers.jinja_template import render_jinja_payload_from_file
+from cloudinit import log
+from cloudinit.sources import INSTANCE_JSON_FILE
+from cloudinit import util
+from . import addLogHandlerCLI, read_cfg_paths
+
+NAME = 'render'
+DEFAULT_INSTANCE_DATA = '/run/cloud-init/instance-data.json'
+
+LOG = log.getLogger(NAME)
+
+
+def get_parser(parser=None):
+    """Build or extend and arg parser for jinja render utility.
+
+    @param parser: Optional existing ArgumentParser instance representing the
+        subcommand which will be extended to support the args of this utility.
+
+    @returns: ArgumentParser with proper argument configuration.
+    """
+    if not parser:
+        parser = argparse.ArgumentParser(prog=NAME, description=__doc__)
+    parser.add_argument(
+        'user_data', type=str, help='Path to the user-data file to render')
+    parser.add_argument(
+        '-i', '--instance-data', type=str,
+        help=('Optional path to instance-data.json file. Defaults to'
+              ' /run/cloud-init/instance-data.json'))
+    parser.add_argument('-d', '--debug', action='store_true', default=False,
+                        help='Add verbose messages during template render')
+    return parser
+
+
+def handle_args(name, args):
+    """Render the provided user-data template file using instance-data values.
+
+    Also setup CLI log handlers to report to stderr since this is a development
+    utility which should be run by a human on the CLI.
+
+    @return 0 on success, 1 on failure.
+    """
+    addLogHandlerCLI(LOG, log.DEBUG if args.debug else log.WARNING)
+    if not args.instance_data:
+        paths = read_cfg_paths()
+        instance_data_fn = os.path.join(
+            paths.run_dir, INSTANCE_JSON_FILE)
+    else:
+        instance_data_fn = args.instance_data
+    try:
+        with open(instance_data_fn) as stream:
+            instance_data = stream.read()
+        instance_data = util.load_json(instance_data)
+    except IOError:
+        LOG.error('Missing instance-data.json file: %s', instance_data_fn)
+        return 1
+    try:
+        with open(args.user_data) as stream:
+            user_data = stream.read()
+    except IOError:
+        LOG.error('Missing user-data file: %s', args.user_data)
+        return 1
+    rendered_payload = render_jinja_payload_from_file(
+        payload=user_data, payload_fn=args.user_data,
+        instance_data_file=instance_data_fn,
+        debug=True if args.debug else False)
+    if not rendered_payload:
+        LOG.error('Unable to render user-data file: %s', args.user_data)
+        return 1
+    sys.stdout.write(rendered_payload)
+    return 0
+
+
+def main():
+    args = get_parser().parse_args()
+    return(handle_args(NAME, args))
+
+
+if __name__ == '__main__':
+    sys.exit(main())
+
+
+# vi: ts=4 expandtab