[ovirt-devel] [vdsm] exploring a possible integration between collectd and Vdsm

[Nir Soffer]

On Tue, Oct 11, 2016 at 2:05 PM, Francesco Romani <fromani at redhat.com> wrote:
> Hi all,
>
> In the last 2.5 days I was exploring if and how we can integrate collectd and Vdsm.

Some comments regarding storage high watermarks only. I will comment later
on other aspects.

> The final picture could look like:
> 1. collectd does all the monitoring and reporting currently Vdsm does
> 2. Engine consumes data from collectd
> 3. Vdsm consumes *notifications* from collectd - for few but important tasks like Drive high water mark monitoring

Drive high watermark is our core business,  we cannot outsource
it to collectd.

Vdsm will always monitor high watermarks directly from libvirt.

> Benefits (aka: why to bother?):
> 1. less code in Vdsm / long-awaited modularization of Vdsm
> 2. better integration with the system, reuse of well-known components
> 3. more flexibility in monitoring/reporting: collectd is special purpose existing solution
> 4. faster, more scalable operation because all the monitoring can be done in C

If the problem in monitoring is python, we can have small and simple
helper doing the monitoring (for storage), like ioprocess.

> At first glance, Collectd seems to have all the tools we need.
> 1. A plugin interface (https://collectd.org/wiki/index.php/Plugin_architecture and https://collectd.org/wiki/index.php/Table_of_Plugins)
> 2. Support for notifications and thresholds (https://collectd.org/wiki/index.php/Notifications_and_thresholds)

Setting threshhold and getting notifications when treshold is reached
sounds like the best design for monitoring drive high watermarks.

But I would like to depend on component that does *only* this task, and
service only vdsm.

> 3. a libvirt plugin https://collectd.org/wiki/index.php/Plugin:virt
>
> So, the picture is like
>
> 1. we start requiring collectd as dependency of Vdsm
> 2. we either configure it appropriately (collectd support config drop-ins: /etc/collectd.d) or we document our requirements (or both)
> 3. collectd monitors the hosts and libvirt
> 4. Engine polls collectd
> 5. Vdsm listens from notifications

Sounds good

>
> Should libvirt deliver us the event we need (see https://bugzilla.redhat.com/show_bug.cgi?id=1181659),
> we can just stop using collectd notifications, everything else works as previously.
>
> Challenges:
> 1. Collectd does NOT consider the plugin API stable (https://collectd.org/wiki/index.php/Plugin_architecture#The_interface.27s_stability)
>    so the plugins should be inclueded in the main tree, much like the modules of the linux kernel
>    Worth mentioning that the plugin API itself has a good deal of rough edges.
>    we will need to maintain this plugin ourselves, *and* we need to maintain our thin API
>    layer, to make sure the plugin loads and works with recent versions of collectd.
> 2. the virt plugin is out of date, doesn't report some data we need: see https://github.com/collectd/collectd/issues/1945
> 3. the notification message(s) are tailored for human consumption, those messages are not easy
>    to parse for machines.
> 4. the threshold support in collectd seems to match values against constants; it doesn't seem possible
>    to match a value against another one, as we need to do for high water monitoring (capacity VS allocation).
>
> How I'm addressing, or how I plan to address those challenges (aka action items):
> 1. I've been experimenting with out-of-tree plugins, and I managed develop, build, install and run
>    one out-of-tree plugin: https://github.com/mojaves/vmon/tree/master/collectd
>    The development pace of collectd looks sustainable, so this doesn't look such a big deal.
>    Furthermore, we can engage with upstream to merge our plugins, either as-is or to extend existing ones.
> 2. Write another collectd plugin based on the Vdsm python code and/or my past accelerator executable project
>    (https://github.com/mojaves/vmon)
> 3. patch the collectd notification code. It is yet another plugin
>    OR
> 4. send notification from the new virt module as per #2, bypassing the threshold system. This move could preclude
>    the new virt module to be merged in the collectd tree.
>
> Current status of the action items:
> 1. done BUT PoC quality
> 2. To be done (more work than #1/possible dupe with github issue)
> 3. need more investigation, conflicts with #4
> 4. need more investigation, conflicts with #3
>
> All the code I'm working on will be found on https://github.com/mojaves/vmon
>
> Comments are appreciated
>
> --
> Francesco Romani
> RedHat Engineering Virtualization R & D
> Phone: 8261328
> IRC: fromani