[openstack-dev] [devstack] Overriding settings file for devstack plugin

Deepak Shetty dpkshetty at gmail.com
Wed Mar 25 10:54:10 UTC 2015


On Wed, Mar 25, 2015 at 4:20 PM, Deepak Shetty <dpkshetty at gmail.com> wrote:

>
>
> On Wed, Mar 25, 2015 at 3:58 PM, Sean Dague <sean at dague.net> wrote:
>
>> On 03/25/2015 03:16 AM, Deepak Shetty wrote:
>> >
>> >
>> > On Wed, Mar 25, 2015 at 11:29 AM, Deepak Shetty <dpkshetty at gmail.com
>> > <mailto:dpkshetty at gmail.com>> wrote:
>> >
>> >
>> >
>> >     On Wed, Mar 25, 2015 at 12:58 AM, Ian Wienand <iwienand at redhat.com
>> >     <mailto:iwienand at redhat.com>> wrote:
>> >
>> >         On 03/24/2015 03:17 PM, Deepak Shetty wrote:
>> >         > For eg: Look at [1]
>> >         > [1]
>> https://github.com/stackforge/devstack-plugin-glusterfs/blob/master/devstack/settings
>> >
>> >         > I would like ability to change these while I use the
>> enable_plugin
>> >         > apporach to setup devstack w/ GlusterFS per my local
>> glusterfs setup
>> >
>> >         So I think the plugin should do
>> >
>> >
>>  CINDER_ENABLED_BACKENDS=${CINDER_ENABLED_BACKENDS:-glusterfs:glusterfs,lvm:lvm1}
>> >
>> >         i.e. provide a default only if the variable is unset.
>> >
>> >
>> >     Bah! That was easy, i should have figured that myself :)
>> >     Thanks for catching that
>> >
>> >
>> >
>> >         This seems like one of those "traps for new players" and is one
>> >         concern I have with devstack plugins -- that authors keep
>> having to
>> >         find out lessons learned independently.  I have added a note on
>> this
>> >         to the documentation in [1].
>> >
>> >         -i
>> >
>> >         [1] https://review.openstack.org/#/c/167375/
>> >
>> >
>> >     Great, i +1'ed it.
>> >
>> >     Also i posted patch to fix settings file @
>> >     https://review.openstack.org/167494
>> >
>> >
>> > Ian,
>> >    Looks like usign bash default in settings file of plugin is not
>> > working, in my patch it didn't use glusterfs driver, it used LVM
>> (default)
>> > I think whats happening here is that by the time settings file is
>> > sourced, CINDER_ENABLED_BACKENDS is already set to lvm by lib/cinder
>> > so settings file's default value is never taken
>> >
>> > IIUC there are 3 scenarios (taking CINDER_ENABLED_BACKENDS as example
>> var) :
>> >
>> > 1) localrc doesn't have CINDER_ENABLED_BACKENDS and enable_plugin
>> >     - Here we want the lib/cinder's default value to be taken
>> >     - this should work fine
>> >
>> > 2) localrc doesn't have CINDER_ENABLED_BACKENDS but has enable_plugin
>> > glusterfs
>> >     - Here we want the plugin's default values to be taken, but its not
>> > as lib/cinder already initialized CINDER_ENABLED_BACKENDS to use lvm
>> backend
>> >     - Thus broken
>> >
>> > 3) localrc has both CINDER_ENABLED_BACKENDS and enable_plugin glusterfs
>> > specified
>> >     - Here we want CINDER_ENABLED_BACKENDS present in my localrc to be
>> > chosen
>> >     - This will work as by the time settings file is sourced
>> > CINDER_ENABLED_BACKENDS is already initialised to my value in localrc
>> >
>> > So #2 scenario would need some changes in stack.sh handling of plugin
>> code ?
>>
>> Right, so this code runs late enough that you don't get to change the
>> defaults. I think that's ok.
>>
>> I would instead do the following:
>>
>> 1) CINDER_ENABLED_BACKENDS+=,glusterfs:glusterfs
>>
>> or
>>
>> 2) CINDER_ENABLED_BACKENDS=glusterfs:glusterfs
>>
>> in the plugin.
>>
>> Clearly, if you've enabled the plugin, you want glusterfs. I think that
>> in most cases you probably only want glusterfs as your backend, so
>> option #2 seems sensible.
>>
>
>
> #1 is needed for multi-backend testing
> #2 is needed for single-backend testing
>
> #2 is what we currently, we blindly override the var, but that forces the
> devstack user to
> use the config given in the plugin, I wanted a way to either use plugin
> config or override it
>
> I think #1 is better, since it gives the power in localrc to do:
>
> 1) CINDER_ENABLED_BACKENDS=
> This will ensure lib/cinder doesn't populate it and plugin adds
> glusterfs:glusterfs for single backend
>

My bad here, lib/cinder uses :- which IIUC means empty or unset, use default
so with #1 or #2 there isn't a way to provide ability to use plugin config
or override it , both ?

back to square one.

thanx,
deepak


>
> 2) No mention of CINDER_ENABLED_BACKENDS in localrc
> This will make it CINDER_ENABLED_BACKENDS=lvm:lvm-driver1,
> glusterfs:glusterfs for multi-backend
>
> Also for vars in settings file that are backend specific (hence not
> touched by lib/cinder):
>
> GLUSTERFS_LOOPBACK_DISK_SIZE & CINDER_GLUSTERFS_SHARES
>
> They can remain as :
> GLUSTERFS_LOOPBACK_DISK_SIZE=${GLUSTERFS_LOOPBACK_DISK_SIZE:-8G}
>
> CINDER_GLUSTERFS_SHARES=${CINDER_GLUSTERFS_SHARES:-"127.0.0.1:
> /vol1;127.0.0.1:/vol2"}
>
> (as mentioned in the patch @
> https://review.openstack.org/#/c/167494/1/devstack/settings)
>
> This will give the end user the ability to change loopback size and/or
> gluster server IPs
> based on the needs of his/her local setup
>
> Agree ?
>
> If yes, then we must mention this in the plugin.rst in a nice way for
> other plugin writers to
> understand properly :) ?
>
> thanx,
> deepak
>
>
>>
>>
>>         -Sean
>>
>> --
>> Sean Dague
>> http://dague.net
>>
>>
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>
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