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Re: [Spacewalk-list] How to update running applications?



Thank you Michael for all of your valuable feedback.

Yes, ooffice is not the best example. I just wanted to illustrate that operators will be working against a GUI, which can't just restart apparently out of its own volition whenever there's an update.

For starters, RPM is a package format, yum is the updater. Deciding when you want to do updates is a good thing to be thinking about. Configuring spacewalk to /not/ pull down updates automatically is I presume doable (spacewalk folks?), in which case you can just push them out when you want (Spacewalk also have a facility to do this as well and can probably explain better).

Maybe I wasn't clear with my previous mail. I do understand the difference between RPM and YUM. I know that from the spacewalk POV I could push the updates at specific times, but to the best of my knowledge this gives me no guarantee the updates will be applied to the clients at a specific time. Furthermore, I'm thinking of administering as much as well over a thousand hosts this way, in an environment were mantainance windows could be quite impractical to enforce. Thus I though of having the yum-rhn plugin download all rpms in the backgound, while the app might be running, and have them installed when I know I can restart the app without inconveniences. I'd also have to ensure that the app can't be started while an update is taking place.

I hope with this I took care of any preceding ambiguities in my intentions.

So I restate my questions: Do you consider this a terrible solution? Am I trying to defeat RPM/YUM/Spacewalk design with this? Is there a better alternative?

Thank you all.

Adrián.

Michael DeHaan escribió:
Adrián Márques wrote:
Thanks a lot Michael.
I'd never heard of condrestart before and your other suggestions also seem to be more than worth checking out.

If I understood you correctly though, the advice you are giving me is geared towards updating services and in the process starting/stopping/restarting them based on conditions (I'll be looking into the links you provided to verify whether this is right). The conundrum I'm facing is that this is a desktop app, picture ooffice as an example, and I can't restart it while the users are logged in it.

office doesn't have a backend service, so that may not be the best example.

In either case, you'd want to deploy your new software in a window where it made since to do it.
The hosts were this app will be running will be dedicated, so I'm leaning towards the idea of hacking the spacewalk client as I mentioned before (so it won't install the updates until told to) and periodically install downloaded rpms either at boot time or whenever I can ensure that no users are logged into this app. Do you consider this a terrible solution? Am I trying to defeat RPM with this? Is there a better alternative?

For starters, RPM is a package format, yum is the updater. Deciding when you want to do updates is a good thing to be thinking about. Configuring spacewalk to /not/ pull down updates automatically is I presume doable (spacewalk folks?), in which case you can just push them out when you want (Spacewalk also have a facility to do this as well and can probably explain better).



Thanks.

Adrián.

Michael DeHaan escribió:
Gerhardus Geldenhuis gta-travel com wrote:
Hi Adrián,
The question is probably more suitable on a rpm list.
We don't distribute our jar's with rpm but I appreciate your dillema.

I don't personnally think that for such complex applications, rpm is the right way to upgrade with. I see rpm has a way to distribute "core" stuff, and not suitable for distributing weird and wonderfull applications that requires restarts and database upgrades etc. There is application servers and frameworks that is better suited for this type of thing and that sits on a logically higher level. JBoss, Wesphere and I think even tomcat has some basic stuff build in.

Regards


This is generally true only for applications that are packaged /poorly/. Properly packaged RPMs can be configured to do "condrestart" as needed.

If you need something more advanced, this is typically where you would want to look at something like puppet/cfengine/bcfg2 where you can describe the state you want your services to be (and remain) in.

Also you may be interested in a simple tool such as Func (http://fedorahosted.org/func) for restarting services remotely. It is in many ways easier to deploy than SSH and also provides you a way of defining arbitrary groups of systems to send commands to.

--Michael
-----Original Message-----
From: spacewalk-list-bounces redhat com [mailto:spacewalk-list-bounces redhat com] On Behalf Of Adrián Márques
Sent: 06 October 2008 18:45
To: spacewalk-list redhat com
Subject: [Spacewalk-list] How to update running applications?

Dear all,

I'm having a difficult time in finding the correct forum to pose this question since I guess it's part spacewalk, part RPM, part basic aplication design.

Being an RPM end-user for years I had always assumed that updating running apps was a piece of cake with RPM. After all, I always did it and the most I got were occasional messages such as "Firefox restart required", never encountering other side-effects.

However, after reading through the RPM guide, getting my hands dirty trying to package an app, scouring the internet for info and asking around in the RPM mailing list, I'm still not sure how to write my RPM so updating won't be an issue.

The scenario is the following: I'd like to use spacewalk to distribute a custom desktop app. Hence, it's unavoidable that some users will be working at the time of an update. So far I've identified two problems with this, 1) If I have to modify the app's database schema as part of the update, the running app might break down if it's not aware of the change 2) This happens to be a java app, so in case a jar gets updated a class might get loaded that is not compatible with those already loaded by the running app.

I understand that what I've explained so far might be outside of the scope of the subjects treated in this mailing list, if so, please just treat it as a detailed background problem description.

What I would like to know from you guys is whether you've had any problems when updating apps through Satellite/Spacewalk due to them being running at the time or what precautions (if any) you take when doing so.

Finally, I suppose that as a last resort I could hack the spacewalk client to only download updates and not install them until it is told to do so from the command line. Is this already possible? If not, where's the place to start with hacking this?

I thank you all for your time and attention. It'd be amazing if you had any comments regarding my background issue, but I'll be more than satisfied and grateful if you could just provide any feedback on those questions strictly spacewalk-related.

Thanks.

Adrián.





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