Open Stack

Hi guys,

Unfortunately I haven't been on Tokio summit but I know that there was
discussion about dynamic reloading of configuration.
Etherpad refs:
https://etherpad.openstack.org/p/mitaka-cross-project-dynamic-config-services
,
https://etherpad.openstack.org/p/mitaka-oslo-security-logging

In this thread I want to discuss agreements reached on the summit and
discuss
implementation details.

Some notes taken from etherpad and my remarks:

1. "Adding "mutable" parameter for each option."
"Do we have an option mutable=True on CfgOpt? Yes"
---------------------------------------------------------
As I understood 'mutable' parameter must indicate whether service contains
code responsible for reloading of this option or not.
And this parameter should be one of the arguments of cfg.Opt constructor.
Problems:
1. Library's options.
SSL options ca_file, cert_file, key_file taken from oslo.service library
could be reloaded in nova-api so these options should be mutable...
But for some projects that don't need SSL support reloading of SSL options
doesn't make sense. For such projects this option should be non mutable.
Problem is that oslo.service - single and there are many different projects
which use it in different way.
The same options could be mutable and non mutable in different contexts.
2. Support of config options on some platforms.
Parameter "mutable" could be different for different platforms. Some
options
make sense only for specific platforms. If we mark such options as mutable
it could be misleading on some platforms.
3. Dependency of options.
There are many 'workers' options(osapi_compute_workers, ec2_workers,
metadata_workers, workers). These options specify number of workers for
OpenStack API services.
If value of the 'workers' option is greater than '1' instance of
ProcessLauncher is created otherwise instance of ServiceLauncher is created.
When ProcessLauncher receives SIGHUP it reloads it own configuration,
gracefully terminates children and respawns new children.
This mechanism allows to reload many config options implicitly.
But if value of the 'workers' option equals '1' instance of ServiceLauncher
is created.
ServiceLauncher starts everything in single process and in this case we
don't have such implicit reloading.

I think that mutability of options is a complicated feature and I think that
adding of 'mutable' parameter into cfg.Opt constructor could just add mess.

2. "oslo.service catches SIGHUP and calls oslo.config"
---------------------------------------------------------
>From my point of view every service should register list of hooks to reload
config options. oslo.service should catch SIGHUP and call list of
registered
hooks one by one with specified order.
Discussion of such implementation was started in ML:
http://lists.openstack.org/pipermail/openstack-dev/2015-September/074558.html
.
Raw reviews:
https://review.openstack.org/#/c/228892/,
https://review.openstack.org/#/c/223668/.

3. "oslo.config is responsible to log changes which were ignored on SIGHUP"
---------------------------------------------------------
Some config options could be changed using API(for example quotas) that's
why
oslo.config doesn't know actual configuration of service and can't log
changes of configuration.

Regards, Marian Horban
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