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Subject: Re: The Case for a Universal Web Server Load Value
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Date: Wed, 14 Nov 2012 14:19:37 -0800
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On Nov 14, 2012, at 11:01, Tim Bannister <isoma@jellybaby.net> wrote:

>> I really like how Perlbal does it:
>>=20
>> It opens a connection when it thinks it needs more and issues a (by =
default, it's configurable) "OPTIONS *" request and only after getting a =
successful response to the test will it send real requests on that =
connection (and then it will keep the connection open with Keep-Alive =
for further requests).
>=20
> X-Server-Load: would still be an improvement, eg with this response to =
OPTIONS:
> HTTP/1.1 200 OK
> Date: Wed, 14 Nov 2012 19:00:00 GMT
> Server: Apache/2.5.x
> X-Server-Load: 0.999
>=20
> =85the balancer might decide to use a backend that is reporting a =
lower load.

I know I am fighting the tide here, but it's really the wrong smarts to =
put in the load balancer.

The backend should/can know if it can take more requests.  When it can't =
it shouldn't and the load balancer shouldn't pass that back to the =
end-user but rather just find another available server or hold on to the =
request until one becomes available (or some timeout value is met if =
things are that bad).

With the "Perlbal-model" the backend can control how much work it will =
take on and the load balancer will never send traffic to an overloaded =
or hung server, so the users will always get to the first truly =
available backend.

The load balancer smarts should be in managing these "let's see if you =
are ready" requests and "pending" connections.


Ask

--=20
Ask Bj=F8rn Hansen, http://askask.com/