[ClusterLabs] Antw: Re: Apache graceful restart not supported by heartbeat apache control script

[Cole Miller]

Hi,

Thank you very much Andrei, Ken and Ulrich for your input! 

I should have mentioned that I did start with trying apachectl graceful, but it fails to find the process because the httpd process is not being run via systemd.

The explanation of why this capability is not present in the control script makes sense, configuration of httpd is outside the scope of the clustering software.

I will proceed with my workarounds that I have found so far. 

Thank you all again so much for your quick help.

Best regards, 
Cole

> On Mar 26, 2019, at 12:02 AM, Ulrich Windl <Ulrich.Windl at rz.uni-regensburg.de> wrote:
> 
>>>> Ken Gaillot <kgaillot at redhat.com> schrieb am 25.03.2019 um 20:03 in
> Nachricht
> <a227e94c55459af8c04ae9fe6f11438fdd6ddd32.camel at redhat.com>:
>> On Mon, 2019-03-25 at 10:42 -0700, Cole Miller wrote:
>>> Hi users at clusterlabs.org,
>>> 
>>> My current project at work is a two node cluster running apache and
>>> virtual IPs on CentOS 7. I found in my testing that apache when run
>>> by corosync does not have a reload or graceful restart. Before the
>>> cluster, when apache was a single instance, I previously used
>>> graceful restart to be able to add configurations with out affecting
>>> current users of the system.
>>> 
>>> Initially, I tried adding the capability myself as a resource action
>>> in the pcs configuration, I was able to add the action, but it would
>>> have no effect when run. Digging deeper, I eventually found the
>>> apache control script at /usr/lib/ocf/resource.d/heartbeat/apache and
>>> was able to see that there are no commands available for a graceful
>>> restart, only graceful stop. 
>>> 
>>> Currently, I have found two ways of getting around this limitation.
>>> The first is “/bin/kill -USR1 `cat /var/run/httpd.pid`", and the
>>> second is "/bin/test -f /var/run/httpd.pid && /usr/sbin/httpd -f
>>> /etc/httpd/conf/httpd.conf -c "PidFile /var/run/httpd.pid" -k
>>> graceful”. Both seem to work with out adversely affecting corosync.
>> 
>> Hi,
>> 
>> apachectl (apache2ctl on some distros) is an easier interface, i.e.
>> "apachectl graceful"
>> 
>>> My primary question is; what is the reason that graceful restart is
>>> not supported by the heartbeat apache control script? It seems like a
>>> pretty common usage of apache, so it seems a strange omission from
>>> the script. I am concerned that I’m trying to work against the grain
>>> since it is absent from the script.
>> 
>> Like an init script, an OCF script is mainly intended for the system
>> (the cluster in this case) to bring a service up or down, and then
>> secondarily as a user interface for doing such actions. The cluster
>> won't ever need or use a graceful restart command, so there hasn't been
>> a demand for an OCF interface to it.
> 
> But there is a "reload" operation defined for OCF RA agents.
> 
>> 
>> I would just use apachectl for reloads and graceful restarts. Neither
>> should affect pacemaker's monitoring (as long as they succeed). (By
>> contrast, you shouldn't use apachectl to do a full start or stop if
>> apache is being controlled by the cluster, because the cluster will see
>> that as a failure.)
> 
> On gracefule restart: IMHO the RA could always try to do a graceful restart,
> and only after some timeout had expired, it should switch to an immediate stop
> of apache. You might compare it to the Xen RA: It always tried to shut down VMs
> cleanly; only after a timeout expired the VMs are terminated the hard way.
> 
>> 
>> A side note: there is a "reload" action supported by some OCF agents,
>> but its use is muddled in pacemaker right now. There is an effort to
>> clear that up, after which we will likely implement a user interface
>> for natively reloading a service. It would make sense for the apache
>> agent to use a graceful restart for that action. So, in the longer
>> term, there might be a way to do what you want via cluster tools.
> 
> Seems we agree on that ;-)
> 
> Regards,
> Ulrich
> 
>> 
>>> My second question is; are the two work arounds presented above safe
>>> for use with corosync/heartbeat/pcs? Is one preferable to the other?
>>> If neither are safe, how would you recommend being able to update
>>> apache configurations with no downtime?
>>> 
>>> I am new to this list and could not find a way to search the
>>> archives, so if this question has already been answered, could you
>>> point me to the search area and to the answer as well?
>>> 
>>> Thank you in advance for your advice and recommendations.
>>> -Cole
>> -- 
>> Ken Gaillot <kgaillot at redhat.com>
>> 
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