swarming: Add server-side implementation for supplemental bot_config

appengine/swarming/handlers_bot.py

 # Copyright 2015 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.
 
 """Internal bot API handlers."""
 
 import base64
 import json
 import logging
 import re
@@ skipping 222 matching lines @@
   # Bot identifier, extracted from 'id' dimension.
   bot_id = None
   # Version of the bot code, as reported by the bot itself.
   version = None
   # Dict with bot state (as reported by the bot).
   state = None
   # Dict with bot dimensions (union of bot-reported and server-side ones).
   dimensions = None
   # Instance of BotGroupConfig with server-side bot config (from bots.cfg).
   bot_group_cfg = None
+  # Supplemental bot_config to inject into the bot.
+  bot_config = None
   # Bot quarantine message (or None if the bot is not in a quarantine).
   quarantined_msg = None
 
   def __init__(self, **kwargs):
     for k, v in kwargs.iteritems():
       # Typo catching assert, ensure _ProcessResult class has the attribute.
       assert hasattr(self, k), k
       setattr(self, k, v)
 
 
@@ skipping 177 matching lines @@
 
     data = {
       'bot_version': bot_code.get_bot_version(self.get_bot_contact_server())[0],
       'server_version': utils.get_app_version(),
       'bot_group_cfg_version': res.bot_group_cfg.version,
       'bot_group_cfg': {
         # Let the bot know its server-side dimensions (from bots.cfg file).
         'dimensions': res.bot_group_cfg.dimensions,
       },
     }
+    if res.bot_group_cfg.bot_config_script:

[Vadim Sh., 2017/02/10 22:08:00]

I've realized there's no mechanism that triggers a reload of config script
changes. The existing mechanism based on 'bot_group_cfg_version' will trigger a
reload if _name_ of bot_config_script changes, not its content.

And even if we extend to include bot_config_script body into
bot_group_cfg_version hash, this mechanism currently reboots bots, which is too
heavyweight for config changes (e.g. we don't want to reboot the entire Chrome
pool when changing configs). 

+      _, script = config.config.get_self_config(
+          'scripts/' + res.bot_group_cfg.bot_config_script,
+          store_last_good=True)
+      logging.info(
+          'Injecting %s: %d bytes',
+          res.bot_group_cfg.bot_config_script,
+          len(script or ''))
+      if not script:
+        # Return an internal error, so that the bot retries slowly.
+        msg = 'Failed to find %s' % res.bot_group_cfg.bot_config_script
+        logging.error(msg)
+        self.abort(503, msg)
+      data['bot_config'] = script
     self.send_response(data)
 
 
 class BotPollHandler(_BotBaseHandler):
   """The bot polls for a task; returns either a task, update command or sleep.
 
   In case of exception on the bot, this is enough to get it just far enough to
   eventually self-update to a working version. This is to ensure that coding
   errors in bot code doesn't kill all the fleet at once, they should still be up
   just enough to be able to self-update again even if they don't get task
@@ skipping 458 matching lines @@
       ('/swarming/api/v1/bot/poll', BotPollHandler),
       ('/swarming/api/v1/bot/server_ping', ServerPingHandler),
       ('/swarming/api/v1/bot/task_update', BotTaskUpdateHandler),
       ('/swarming/api/v1/bot/task_update/<task_id:[a-f0-9]+>',
           BotTaskUpdateHandler),
       ('/swarming/api/v1/bot/task_error', BotTaskErrorHandler),
       ('/swarming/api/v1/bot/task_error/<task_id:[a-f0-9]+>',
           BotTaskErrorHandler),
   ]
   return [webapp2.Route(*i) for i in routes]