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List:       haproxy
Subject:    Re: realtime switch to another backend if got 5xx error?
From:       Jonah Horowitz <jhorowitz () looksmart ! net>
Date:       2009-07-30 23:05:05
Message-ID: C6977531.191E9F%jhorowitz () looksmart ! com
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I'm trying to figure out how this works.  I desperately need to figure out a
way to monitor servers and either take any server that sends any 5xx error
out of rotation, or failing that, at least redirect the query to a different
server.

The clients that use this web service are SOAP/XML clients, so they're not
"real" web browsers.  Also, we don't use any cookies.

It looks like this config just tells the client to make a second request.
Am I missing something here?

I know I can use httpchk, but I don't want to run "inter 1" because then all
my traffic is monitoring traffic.  Each server is normally doing several
hundred requests per second, and our haproxy test setup is a couple orders
of magnitude higher on % of 500 errors. (10% vs .01%).

Any ideas?

Thanks,

Jonah



On 6/11/09 7:45 AM, "Maciej Bogucki" <macbogucki@gmail.com> wrote:

> Dawid Sieradzki / Gadu-Gadu S.A. pisze:
>> Hi.
>> 
>> The problem is how to silent switch to another backend in realtime if
>> got 500 answer from backend, without http_client knowledge
>> Yes i know, httpchk, but the error 500 is 10 per hour, we don't know
>> when and why.
>> So, it is a race who get 500 first - httpchk or http_client.
>> 
>> If You don't know what i mean:
>> 
>> example config:
>> 
>> ----8<--------
>> 
>> frontend
>> (..)
>> default_backend back_1
>> 
>> backend back_1
>>    option httpchk GET /index.php HTTP/1.1\r\nHost:\ test.pl
>>    mode http
>>    retries 10
>>    balance roundrobin
>> 
>>  server chk1 127.0.0.1:81 weight 1 check
>>  server chk2 127.0.0.1:82 weight 1 check
>>  server chk3 127.0.0.1:83 weight 1 check backup
>> 
>> ---->8----------
>> 
>> http_client -> haproxy -> (backend1|backend2|backend3)
>> 
>> let's go inside request:
>> 
>> A. haproxy recived request from http_client
>> B. haproxy sent request from http_client to backend1
>> C. backend1 said 500 internal server error
>> 
>> I want: :-)
>> D. haproxy sent request from_http to backend2 (or backup backend or
>> another one, or one more time to backend1)
>> 
>> I have: :-(
>> D. haproxy sent 500 internal server error to http_client from backend1
>> E. haproxy will mark backend1 as down if got 2 > errror 500 from backend1
>> 
>> 
>> It is possible to do that?
>> 
> Hello,
> 
> Yes it is possible but it could be dengerous for some kinde of
> application fe. billing system ;)
> Here is an example how to do it. I know that it is the hack but it works
> good ;P
> 
> frontend fr1
>         default_backend back_1
>         rspirep         ^HTTP/...\ [23]0..* \0\nSet-Cookie:\
> cookiexxx=0;path=/;domain=.yourdomain.com
>         rspirep         ^(HTTP/...)\ 5[0-9][0-9].* \1\ 202\ Again\
> Please\nSet-Cookie:\
> cookiexxx=1;path=/;domain=.yourdomain.com\nRefresh:\ 6\nContent-Length:\
> Lenght_xxx\nContent-Type:\ text/html\n\n<FRAMESET\ cols="100%"><FRAME\
> src="http://www.yourdomain.com/redispatch.pl">
> 
> backend back_1
>          cookie          cookiexxx
>          server chk1 127.0.0.1:81 weight 1 check
>          server chk2 127.0.0.1:82 weight 1 check
>          server chk3 127.0.0.1:83 weight 1 check cookie 1 backup
> 
> Remember to set Lenght_xxx properly.
> 
> Best Regards
> Maciej Bogucki
> 
> 

-- 
Jonah Horowitz · Monitoring Manager · jhorowitz@looksmart.net
W: 415-348-7694 · F: 415-348-7033 · M: 415-513-7202
LookSmart - Premium and Performance Advertising Solutions
625 Second Street, San Francisco, CA 94107




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