[Engine-devel] vdsm checkConnectivity pitfals

[Itamar Heim]

On 12/22/2011 01:05 PM, Roy Golan wrote:
>
> Hi all,
>
> VDSM network provisioning api exposes a validity check to know the newly
> applied changes works. The actual
> check is comparing the /var/run/vdsm/client.log modified time to the
> time when the check began and repeats
> that check after sleeping 1 seconds for X time (where X is
> connectivityTimeOut)
>
> def clientSeen(timeout):
> start = time.time()
> while timeout >= 0:
> if os.stat(constants.P_VDSM_CLIENT_LOG).st_mtime > start:
> return True
> time.sleep(1)
> timeout -= 1
> return False
>
> Main issues I spot are:
> 1. In case the host is in maintenance, the caller of the API must
> generate traffic, concurrently to running api call,
> and then must join and sync threads to realize when all is done. see
> http://gerrit.ovirt.org/#change,584
> 2. locally calling vdsClient also modifies the client.log - we can't
> rely on that no one will do that during the call.
> 3. Failure writing to the client log will fail network provisioning!
>
> All of the above makes it not very reliable as a check and harder to
> call, without posing races, as client.
>
> Possible alternate solution:
> 1. We can try to reach the api caller socket in return, maybe use http
> code 100 ?
> 2. pass in the API a URL which the VDSM will call. could be a
> health-check servlet or something similar.

VDSM calling voirt engine is not a good enough health check. it doesn't 
mean engine can call back.
so you would need VDSM to call an engine URL asking engine to generate 
traffic to VDSM.

replying to Ayal - I think even with QMF you would need to ask to get a 
reply - so mechanism is probably same wrt API, just "URL" may change.