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On Mon, 2008-01-14 at 15:47 -0500, Graeme Fowler wrote:
> Hi
>
> Will cc this to keepalied list as you posted there too :)
>
> On Mon, 2008-01-14 at 11:19 -0500, Scott McClanahan wrote:
> > We run ipvs with keepalived (CentOS 5.1) and often change the
> run-time
> > configuration of real servers by manipulating there weights. Our
> > problem is if the backend real server reboots or the application
> > restarts, the weight gets reset to the value in the keepalived
> config
> > file which is often times not what we want.
>
> You probably need the following (see keepalived.conf.SYNOPSIS or the
> man
> page), edited slightly, in your virtual_server or virtual_server_group
> definitions:
>
> MISC_CHECK { # MISC healthchecker
> misc_path <STRING>|<QUOTED-STRING> # External script or program
> misc_timeout <INTEGER> # Script execution timeout
>
> # If set, exit code from healthchecker is used
> # to dynamically adjust the weight as follows:
> # exit status 0: svc check success, weight
> # unchanged.
> # exit status 1: svc check failed.
> # exit status 2-255: svc check success, weight
> # changed to 2 less than exit status.
> # (for example: exit status of 255 would set
> # weight to 253)
> misc_dynamic
> }
>
> My reading of that is that you replace your healthcheck scripts with a
> MISC_CHECK that can lookup the set weight in some way (in a file, a
> database, or by parsing the output from ipvsadm - TMTOWTDI, in Perl
> parlance) and then return a value appropriate to your circumstance.
>
> Example:
>
> You configure an HTTP realserver with weight 100 in keepalived.conf.
> You
> have a MISC_CHECK script which uses wget, LWP or something to check
> the
> web service is running.
>
> You want to turn the weight down to 75.
>
> Your MISC_CHECK script, as well as doing a health check, can do a
> lookup
> in a file (say /etc/keepalived/weights/$virtual_server). If the file
> doesn't exist, skip the weight setting. If it does, read the contents
> and set the return code appropriately.
>
> For the avoidance of confusion, you put the *real* weight - 75 - in
> the
> file. The MISC_CHECK then does some meta-logic:
>
> Is the service healthy?
> No? Exit 1 (ie. fail)
> Yes?
> Does /etc/keepalived/weights/$virtual_server exist?
> No? Skip this part.
> Yes? Read the file and fetch $value.
> Is the value numeric, from 2-255?
> No? Log the error, Exit 0 (ie. success)
> Yes?
> Exit $value+2 (ie. success, change weight to $value)
>
> This is untried/untested but if I read you right it should work.
>
> The joy of this is that the weight will then remain at whatever you
> set
> it to in the file *and* persist across service, server, keepalived or
> director restarts as long as the file exists.
>
> Graeme
>
Thanks for the response but I think the easiest and best approach for me
would simply be to mod the config with the appropriate weight (this
doesn't happen so frequently that it's a burden) and perform a reload.
I just need to be sure keepalived handles a HUP signal as I'd expect. I
noticed in previous releases HUP signals weren't always handled so
gracefully. I'd like to make sure the master stays master and
interruptions to users are avoided.
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