config: add environment variable substitution

This change enables setting configuration values through
environment variables. This is useful to manage user defined
configuration, such as user password, in Kubernetes deployment.

Change-Id: Ia40510c2b6443ea2a650a45e30b2885197f18c29

tests/fixtures/registry.yaml

@@ -0,0 +1,14 @@
+registry:
+  address: '0.0.0.0'
+  port: 9000
+  public-url: https://localhost:9000
+  tls-cert: /tmp/test/cert.pem
+  tls-key: /tmp/test/cert.key
+  secret: "%(ZUUL_REGISTRY_SECRET)"
+  users:
+    - name: testuser
+      pass: testpass
+      access: write
+  storage:
+    driver: filesystem
+    root: /tmp/test/storage

tests/test_config.py

@@ -0,0 +1,27 @@
+# Copyright 2020 Red Hat, Inc.
+#
+# This module is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This software is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this software.  If not, see <http://www.gnu.org/licenses/>.
+
+import testtools
+
+from zuul_registry.main import RegistryServer
+
+
+class TestRegistryConfig(testtools.TestCase):
+    def test_config_env(self):
+        conf = RegistryServer.load_config("tests/fixtures/registry.yaml", {})
+        self.assertEqual(conf["registry"]["secret"], "%(ZUUL_REGISTRY_SECRET)")
+        conf = RegistryServer.load_config(
+            "tests/fixtures/registry.yaml", dict(ZUUL_REGISTRY_SECRET="42"))
+        self.assertEqual(conf["registry"]["secret"], "42")

zuul_registry/main.py

@@ -21,6 +21,8 @@ import logging
 import cherrypy
 import hashlib
 import json
+import typing
+import functools
 import yaml
 
 from . import filesystem
@@ -310,7 +312,8 @@ class RegistryServer:
 
     def __init__(self, config_path):
         self.log.info("Loading config from %s", config_path)
-        self._load_config(config_path)
+        self.conf = RegistryServer.load_config(
+            config_path, os.environ)['registry']
 
         # TODO: pyopenssl?
         cherrypy.server.ssl_module = 'builtin'
@@ -376,10 +379,17 @@ class RegistryServer:
 
         cherrypy.tree.mount(api, '/', config=conf)
 
-    def _load_config(self, path):
+    @staticmethod
+    def load_config(path: str, env: typing.Dict[str, str]) -> typing.Any:
+        """Replace path content value of the form %(ZUUL_ENV_NAME) with environment,
+           Then return the yaml load result"""
         with open(path) as f:
-            conf = yaml.safe_load(f.read())
+            return yaml.safe_load(functools.reduce(
-        self.conf = conf['registry']
+                lambda config, env_item: config.replace(
+                    f"%({env_item[0]})", env_item[1]),
+                [(k, v) for k, v in env.items() if k.startswith('ZUUL_')],
+                f.read()
+            ))
 
     @property
     def port(self):