> FWIW, there are other ways of avoiding the restarts by preallocating > daemon process groups in advance and not using VirtualHost but other > means of virtual hosting.
Hmm, this is interesting, any example (docs)? On 13 Sty, 12:28, Graham Dumpleton <[email protected]> wrote: > On 13 January 2011 22:14, grassoalvaro <[email protected]> wrote: > > > Thanks. I'll try to modify Apache source code to change that timeout > > and then make some tests. > > Have fun trying to work out where to change it. It seems to differ > between MPMs and I never quite got my head around it completely, or at > least I have forgotten exactly how it works. Overall It is not > something I would recommend and increasing the timeout will likely > only cause other problems. That is, rather than have requests be > killed, you will cause new requests to stall for a lot longer and > sites will simply appear to not be responding. > > > Event if mod_wsgi wan't create for shared hosting - many people use it > > for this. And it works well (except Apache reloading ;-)) Solution to > > use one Apache for one client is good but takes too many memory. > > FWIW, there are other ways of avoiding the restarts by preallocating > daemon process groups in advance and not using VirtualHost but other > means of virtual hosting. > > Graham > > > Anywany, thanks for information. > > > On 11 Sty, 23:30, Graham Dumpleton <[email protected]> wrote: > >> On 11 January 2011 23:06, grassoalvaro <[email protected]> wrote: > > >> > Thanks for your very useful description. > >> > Do you know Is there any good reason why apache is killing process > >> > after 3 seconds? Why no 15 for example? > > >> It is a hard wired timeout period it applies to Apache child processes > >> when a 'restart' is applied. When it does a graceful restart, it > >> handles its own child process differently and lets them run to > >> completion, but in that graceful restart mode it still kills off > >> processes after fixed 3 seconds if they are what it regards as other > >> processes, which is what it regards mod_wsgi daemon processes. > > >> Note that mod_wsgi was originally intended for self hosting of your > >> own web applications with daemon mode not actually a part of the > >> original goals as far as features. The model of how it is implemented > >> isn't necessarily suited to doing shared hosting, especially where > >> changes are going to be made often to Apache configuration. > > >> Graham > > >> > On 11 Sty, 10:17, Graham Dumpleton <[email protected]> wrote: > >> >> On 11 January 2011 10:27, grassoalvaro <[email protected]> wrote: > > >> >> > Ok, short description is not enought. > > >> >> > My app is an ordering app for shared hosting accounts (for Python > >> >> > mod_wsgi) and it's based on mod_wsgi also. > >> >> > App is calling some API method (server-app) which is restarting apache > >> >> > after httpd modifications. > >> >> > The problem is that I can of course use sleep && httpd graceful in > >> >> > background, but this will kill other (customer apps) connections after > >> >> > sleep. > >> >> > So, is there any method do reload config without killing any mod_wsgi > >> >> > connections? > > >> >> Connections are transient and not permanent. For a well written site > >> >> connections would be maintained for less than a second. > > >> >> The way the process restart works for daemon processes, regardless of > >> >> whether you do an Apache restart or graceful restart, is that when > >> >> daemon process is signalled to restart, it will stop accepting any > >> >> more connections. If there are no active connections for current > >> >> requests it will shutdown process immediately and then restart. Any > >> >> connections that come during that time effectively queue up with > >> >> Apache child processes and/or within port 80 socket listener queue. > >> >> When processes restart, the held over requests will be handled. > > >> >> In the case that the daemon process still had active requests, then > >> >> rather than daemon process shutting down and restarting immediately it > >> >> waits, giving the current requests an opportunity to finish first at > >> >> what point the process is then shutdown and restarted. The way Apache > >> >> works however, is that it gives a maximum of three seconds grace to > >> >> the mod_wsgi daemon processes and if they have not shutdown by then, > >> >> because of the requests not finishing, Apache will forcibly kill them > >> >> off and they will be restarted. > > >> >> The problem you saw was because your request handler was likely > >> >> blocked in some way on waiting for the Apache process to restart and > >> >> that very act meant the request didn't complete within the three > >> >> seconds allowing the process to shutdown cleanly. > > >> >> Now, as I said, for a well written site, requests should be sub > >> >> second, only long requests like large file uploads might be affected. > >> >> So, for typical case, the restart wouldn't usually be noticed and > >> >> wouldn't affect any connections because outstanding requests would > >> >> finish within the three seconds dictated by Apache. > > >> >> Of course, if you are constantly restarting Apache because of > >> >> configuration changes, then you increase the risk that you will hit a > >> >> requests that doesn't finish within the three seconds and exit in time > >> >> to allow process to restart cleanly. > > >> >> Whether you can avoid doing the restarts I cannot comment because have > >> >> no idea what changes you are enacting to the Apache configuration > >> >> which triggers you wanting to restart it. If the changes relate to > >> >> mod_wsgi daemon process provisioning then for some cases you may be > >> >> able to avoid it, but it means setting up things in a particular way. > >> >> Overall, you are often better off having a nginx front end and simply > >> >> giving each customer their own Apache instance behind that. That way > >> >> only customer to whom the changes apply are affected and no one else. > >> >> This is how WebFaction and some other quality Python hosting companies > >> >> work. > > >> >> > Regards. > > >> >> > On 11 Sty, 00:15, Graham Dumpleton <[email protected]> wrote: > >> >> >> On 11 January 2011 07:53, grassoalvaro <[email protected]> > >> >> >> wrote: > > >> >> >> > Hi. > > >> >> >> > I have application deployed on apache + mod_wsgi which is changing > >> >> >> > httpd.conf and then reloading apache (httpd graceful). > >> >> >> > And here is the problem: application is making request changing > >> >> >> > httpd > >> >> >> > config and reloading him and while request is in progress the > >> >> >> > process > >> >> >> > is killing: > > >> >> >> > Premature end of script headers: start.wsgi > >> >> >> > (2)No such file or directory: mod_wsgi (pid=31624): Unable to > >> >> >> > connect > >> >> >> > to WSGI daemon process 'pylons_app' on > >> >> >> > '/var/logs/wsgi.31409.0.1.sock' > >> >> >> > after multiple attempts., > > >> >> >> > So it is possible to reload _only_ apache config without reloading > >> >> >> > whole mod_wsgi? > > >> >> >> The short answer is no. > > >> >> >> > Or any other idea how to deal with this problem? > > >> >> >> How are you triggering the Apache restart? The daemon processes > >> >> >> themselves will not have sufficient privileges to do it itself, so > >> >> >> you > >> >> >> must be using a separate suid script or invoking a remote API for > >> >> >> some > >> >> >> service that does it on your behalf. > > >> >> >> If it is a command line script, then invoke it as a background > >> >> >> command > >> >> >> with a time delay before it. Ie. > > >> >> >> os.system('(sleep 1; /some/path/restart-apache)&') > > >> >> >> If it is via a remote API using XML-RPC or something, instead of > >> >> >> doing > >> >> >> it from web application, make it a script executed as above. > > >> >> >> A further way is to create a background thread which calls the API. > > >> >> >> In all ways, you are attempting to avoid the problem of the request > >> >> >> handler blocking on waiting for the restart command to complete. > > >> >> >> Anyway, will help if you explain how you are triggering the Apache > >> >> >> restart. > > >> >> >> Graham > > >> >> > -- > >> >> > You received this message because you are subscribed to the Google > >> >> > Groups "modwsgi" group. > >> >> > To post to this group, send email to [email protected]. > >> >> > To unsubscribe from this group, send email to > >> >> > [email protected]. > >> >> > For more options, visit this group > >> >> > athttp://groups.google.com/group/modwsgi?hl=en. > > >> > -- > >> > You received this message because you are subscribed to the Google > >> > Groups "modwsgi" group. > >> > To post to this group, send email to [email protected]. > >> > To unsubscribe from this group, send email to > >> > [email protected]. > >> > For more options, visit this group > >> > athttp://groups.google.com/group/modwsgi?hl=en. > > > -- > > You received this message because you are subscribed to the Google Groups > > "modwsgi" group. > > To post to this group, send email to [email protected]. > > To unsubscribe from this group, send email to > > [email protected]. > > For more options, visit this group > > athttp://groups.google.com/group/modwsgi?hl=en. -- You received this message because you are subscribed to the Google Groups "modwsgi" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/modwsgi?hl=en.
