sitescripts: Script to keep services alive

sitescripts/management/bin/start_services.py

 # coding: utf-8
 
 # This file is part of the Adblock Plus web scripts,
 # Copyright (C) 2006-2012 Eyeo GmbH
 #
 # Adblock Plus is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 3 as
 # published by the Free Software Foundation.
 #
 # Adblock Plus 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 Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
 
-import os
+import os, subprocess
 from sitescripts.utils import get_config
 
 def _get_services():
-   config = get_config()
-   section_name = "keep_alive_services"
-   section_keys = config.options(section_name)
-   default_keys = config.defaults().keys()
-   keys = set(section_keys) - set(default_keys)
+  config = get_config()
+  section_name = "keep_alive_services"
+  section_keys = config.options(section_name)
+  default_keys = config.defaults().keys()
+  keys = set(section_keys) - set(default_keys)
 
-   services = {}
-   for key in keys:
-     services[key] = config.get(section_name, key)
-   return services
-
-def _files_exist(files):
-  for file in files:
-    if not os.path.exists(file):
-      print "'%s' does not exist." % file
-      return False
-  return True
+  services = {}
+  for key in keys:
+    services[key] = config.get(section_name, key)
+  return services
 
 def _process_running(pid):
-  return True

[Wladimir Palant, 2012/11/29 15:01:46]

That still needs to be written, right?

[Felix Dahlke, 2012/11/30 09:49:32]

Um, yes. That's sort of important :) Done.

+  try:
+    os.kill(pid, 0)
+    return True
+  except OSError:
+    return False
 
 if __name__ == "__main__":
   services = _get_services()
   for service in services.keys():
-    init_file = "/etc/init.d/%s" % service
-    pid_file = "/var/run/%s" % services[service]

[Wladimir Palant, 2012/11/29 15:01:46]

Use os.path.join() here?

[Felix Dahlke, 2012/11/30 09:49:32]

Done.

+    pid_path = os.path.join("/var/run", services[service])
+    if os.path.exists(pid_path):
+      with open(pid_path) as file:
+        pid_string = file.read()
 
-    if not _files_exist([init_file, pid_file]):

[Wladimir Palant, 2012/11/29 15:01:46]

Actually, if the pid file doesn't exist it means that the service isn't running
- we should start it. And if the init file doesn't exist we should fail -
otherwise we might end up mistakenly relying on this script even though we have
a typo in our configuration.

[Felix Dahlke, 2012/11/30 09:49:32]

Done.

-      continue
+      try:
+        pid = int(pid_string.rstrip())
+        if _process_running(pid):
+          continue
+      except exceptions.ValueError:
+        print "'%s' is not a PID." % pid_string
 
-    pid_file_content = open(pid_file).read().rstrip()

[Wladimir Palant, 2012/11/29 15:01:46]

I generally prefer to close files explicitly...

[Felix Dahlke, 2012/11/30 09:49:32]

Done.

-    try:
-      pid = int(pid_file_content)
-    except exceptions.ValueError:
-      print "'%s' is not a PID." % pid_file_content
-      continue
-
-    if _process_running(pid):
+    init_path = os.path.join("/etc/init.d", service)
+    if not os.path.exists(init_path):
+      print "%s does not exist, service is not running and cannot be started." % init_path
       continue
 
     print "%s is not running, starting ..." % service

[Wladimir Palant, 2012/11/29 15:01:46]

You are aware that any output from a cron job results in a mail to
administrator, right? Then again, maybe that's not a bad thing - if services
need restarting then this justifies a notification.

[Felix Dahlke, 2012/11/30 09:49:32]

Yes, that's what I intended. A crashing service is something we'll want to look
into.

-    subprocess.call([init_file, "start"])
+    subprocess.call([init_path, "start"])