Re: Writing hooks for Perlbal

Raistlin,

I could swear that perlbal already has a health check in place, but the 
other place you would do health checking would be during the callback 
that you registered (that would fire every N seconds.)  Or are you 
looking for something else?

Elliot

Raistlin Majere wrote:
> Elliot,
>     
>     Well, I think I'm onto something.  I've been hacking on Service.pm 
> and the code that spawns new servers.  Around line 1162 I've added a 
> subroutine which verifies that the server is available on the specified 
> ip and port it receives from  $self->{pool}->get_backend_endpoint.  If 
> the server isn't there, then I execute a lot of code and return a new 
> $ip and $port, and then let the subroutine continue.
>
>     I'm a little concerned that this gets executed only when new 
> backends are created, and that if an existing backend with a persistent 
> connection goes down this code won't be executed.  I'd like to find a 
> better place for it and write a 'hook' for it.  Essentially a 'verify' 
> server hook.  Any ideas or suggestions would be appreciated.
>
> -=Raistlin
>
> On 8-Oct-06, at 12:11 PM, Elliot F wrote:
>
> > I would suggest taking a look at the code around the 
> > backend_client_assigned hook.  If you haven't already, take a look at 
> > the doc/hacking/hooks.txt file.
> >
> > I'm not sure, but your problem may quickly get much more complex.  I 
> > would not be surprised if you have to make your own hook somewhere, or 
> > modify perlbal.
> >
> > If the 'backend_client_assigned' hook isn't enough, I'm assuming you 
> > would want to look at './lib/Perlbal/BackendHTTP.pm', and specifically 
> > the 'assign_client' sub around line 159.  I'm not saying this is the 
> > answer, but it would be where I would start looking.
> >
> > Hope that helps,
> >
> > Elliot
> >
> > Raistlin Majere wrote:
> > > Alright, I have the plugin/callback being called.  Looks like I just 
> > > needed to add "plugins = MyPlugin" (where MyPlugin is the package in 
> > > the Perlbal/Plugin directory).
> > > The callback functionality looks useful for polling things and 
> > > reacting accordingly, I've implemented this, however I am curious how 
> > > to rewrite a request to a different backend server.
> > > Ideally I'd like to be able to be able to:
> > > Accept a request to a virtualhost
> > > Verify that the backend server is up and running
> > > if it's not then hold the request while I either:
> > >     a) bring the backend server up
> > >     b) rewrite the request to a different server
> > > Any ideas how to redirect the request, POST data, etc to a different 
> > > machine?
> > > > Raistlin,
> > > >
> > > > Take a look at registering a callback that perlbal will trigger 
> > > > every N seconds.  AtomStream.pm has it being used.  It's called 
> > > > 'Perlbal::Socket::register_callback'.  You would be able to do 
> > > > whatever check(s) you want, and react accordingly (mark it as down 
> > > > somehow, reconfigure perlbal, etc.)  And it wouldn't be doing it for 
> > > > every request.
> > > >
> > > > Just make sure you don't block.  :)
> > > >
> > > > Elliot
> > > >
> > > > Raistlin Majere wrote:
> > > > > I've installed and configured perlbal and have run into some 
> > > > > difficulties.  I've setup perlbal to be a reverse proxy so that it 
> > > > > correctly proxies virtualhosts to the appropriate servers.  (i.e. 
> > > > > vhost1.example.com, vhost2.example.com correctly reverse proxies 
> > > > > for vhost1.com and vhost2.com respectively) This is working 
> > > > > perfectly, and wasn't too difficult to configure.
> > > > > However now I want to write some code that will:
> > > > > First verify that the backend server is alive
> > > > > Second that the backend server can answer requests on the port I'm 
> > > > > trying to talk to
> > > > > And if it's NOT alive and able to respond to requests that I can 
> > > > > redirect requests to a different server, or execute some code to 
> > > > > bring the downed server up, before retrying.
> > > > > I've tried to use the Perlbal::ClientProxy "start_proxy_request" 
> > > > > hook, however that seems to affect each and every request (i.e. 
> > > > > each html page, graphic, etc.)
> > > > > I need to be able to check to see if the backend server is alive, 
> > > > > and if it's not, tell Perlbal: "Whoa hold your horeses" long enough 
> > > > > for me to bring a server up (I can do this with some scripts I 
> > > > > have), and then redirect the request to the new server.
> > > > > Any help or advice would be greatly appreciated.