Adds config component to Machine Provider

appengine/machine_provider/config.py

+# Copyright 2016 The LUCI Authors. All rights reserved.
+# Use of this source code is governed under the Apache License, Version 2.0
+# that can be found in the LICENSE file.
+
+"""Instance specific settings."""
+
+import logging
+
+from components import config
+from components import net
+from components import utils
+from components.config import validation
+
+from proto import config_pb2
+
+SETTINGS_CFG_FILENAME = 'settings.cfg'
+SETTINGS_TS_MON_DEFAULT = True
+
+
+ConfigApi = config.ConfigApi
+
+
+@validation.self_rule(SETTINGS_CFG_FILENAME, config_pb2.SettingsCfg)
+def validate_settings(cfg, ctx):
+  """Validates settings.cfg file against proto message schema."""
+  pass
+
+
+def _get_settings():
+  """Returns (rev, cfg) where cfg is a parsed SettingsCfg message.
+
+  If config does not exists, returns (None, <cfg with defaults>).
+
+  The config is cached in the datastore.
+  """
+  # store_last_good=True tells config component to update the config file
+  # in a cron job. Here we just read from the datastore.
+  rev, cfg = config.get_self_config(
+      SETTINGS_CFG_FILENAME, config_pb2.SettingsCfg, store_last_good=True)
+  cfg = cfg or config_pb2.SettingsCfg()
+  cfg.enable_ts_monitoring = cfg.enable_ts_monitoring or SETTINGS_TS_MON_DEFAULT
+  return rev, cfg
+
+
+@utils.cache_with_expiration(60)
+def settings():
+  """Loads settings from an NDB-based cache or a default one if not present."""
+  return _get_settings()[1]