notify calling process we are ready to serve

Fixes bug 980037

Service managers starting keystone-all have no way of being notified
when the service is ready to accept connections. This commit allows
a configurable command to be called when we are ready e.g.
for systemd setting the statup type of a service unit to "notify" and setting
onready    = systemd-notify --ready
in keystone.conf, would notify a waiting systemd that we are ready to
serve

In an automated envirnment (e.g. puppet) this will allow the startup of
the keystone-all service (with systemctl for example) directly followed
by usage of the keystone client without the need for a sleep (or retry)
while we are waiting for the keystone service to be ready.

Change-Id: I3f7aafe9837be60a0f35cae1a7db892f6851cc47

bin/keystone-all

@@ -20,6 +20,7 @@ from paste import deploy
 
 from keystone import config
 from keystone.common import wsgi
+from keystone.common import utils
 
 
 CONF = config.CONF
@@ -37,6 +38,13 @@ def serve(*servers):
                       server.port)
         server.start()
 
+    # notify calling process we are ready to serve
+    if CONF.onready:
+        try:
+            utils.check_output(CONF.onready.split())
+        except Exception:
+            logging.exception('Failed to execute onready command')
+
     for server in servers:
         try:
             server.wait()

etc/keystone.conf.sample

@@ -46,6 +46,10 @@
 # Format string for %(asctime)s in log records.
 # log_date_format = %Y-%m-%d %H:%M:%S
 
+# onready allows you to run a command when the process is ready to serve
+# for example to have it notify using systemd, one could set
+# onready = systemd-notify --ready
+
 [sql]
 # The SQLAlchemy connection string used to connect to the database
 # connection = sqlite:///keystone.db

keystone/config.py

@@ -143,6 +143,7 @@ register_str('bind_host', default='0.0.0.0')
 register_str('compute_port', default=8774)
 register_str('admin_port', default=35357)
 register_str('public_port', default=5000)
+register_str('onready')
 
 
 # sql options