reloads mutable config values on SIGHUP

This changes the ironic (ironic-api and ironic-conductor)
services so that when a SIGHUP signal is issued, the
service reloads (and uses) the values of mutable configuration
options.

The mutable configuration options (set by oslo.config Opts' mutable=True)
are:
- [DEFAULT]/pin_release_version
- [DEFAULT]/debug
- [DEFAULT]/log_config_append
and are indicated as such in ironic's sample config
(https://docs.openstack.org/ironic/latest/configuration/sample-config.html)
by "# Note: This option can be changed without restarting.".

Configuration options are mutable if their oslo.config Opt's mutable=True
is set. This mutable setting is respected when the oslo method
mutate_config_files is called instead of reload_config_files.
Icec3e664f3fe72614e373b2938e8dee53cf8bc5e allows services to tell
oslo.service they want mutate_config_files to be called by specifying the
'restart_method=mutate' parameter, which this patch does.

Change-Id: I0df46bb21dda035b25daad17737dbfedb861e868
Closes-Bug: #1585595

ironic/cmd/conductor.py

@@ -81,7 +81,7 @@ def main():
 
     profiler.setup('ironic_conductor', CONF.host)
 
-    launcher = service.launch(CONF, mgr)
+    launcher = service.launch(CONF, mgr, restart_method='mutate')
     launcher.wait()
 
 

ironic/common/service.py

@@ -36,4 +36,4 @@ def prepare_service(argv=None):
 
 
 def process_launcher():
-    return service.ProcessLauncher(CONF)
+    return service.ProcessLauncher(CONF, restart_method='mutate')

ironic/conf/default.py

@@ -282,7 +282,7 @@ service_opts = [
                       'hostname, FQDN, or IP address.')),
     cfg.StrOpt('pin_release_version',
                choices=versions.RELEASE_VERSIONS,
-               # TODO(xek): mutable=True,
+               mutable=True,
                help=_('Used for rolling upgrades. Setting this option '
                       'downgrades (or pins) the Bare Metal API, '
                       'the internal ironic RPC communication, and '

releasenotes/notes/sighup-service-reloads-configs-0e2462e3f064a2ff.yaml

@@ -0,0 +1,17 @@
+---
+features:
+  - |
+    Issuing a SIGHUP (e.g. ``pkill -HUP ironic``) to an ironic-api or
+    ironic-conductor service will cause the service to reload and use any
+    changed values for *mutable* configuration options. The mutable
+    configuration options are:
+
+    * [DEFAULT]/debug
+    * [DEFAULT]/log_config_append
+    * [DEFAULT]/pin_release_version
+
+    Mutable configuration options are indicated as such in the `sample configuration
+    file <https://docs.openstack.org/ironic/latest/configuration/sample-config.html>`_
+    by ``Note: This option can be changed without restarting``.
+
+    A warning is logged for any changes to immutable configuration options.