Writing hooks for Perlbal
Elliot F
elliotf-danga-perlbal at gratuitous.net
Wed Oct 11 16:10:11 UTC 2006
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.
>
>
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