Dynamically add/remove mongrel on EC2 from Apache balancer

Rails Deployment
1

Hi,

I’d like to scale out by adding more EC2 mongrel instances, and scale
down by removing EC2 mongrel instances.

Is there a way to dynamically add/remove mongrel instances from Apache
mod_proxy_balancer. It seems that I’d have to manually change the
configuration file and restart apache whenever I add/remove a new
mongrel.

Yaxm

2

Is there a way to dynamically add/remove mongrel instances from Apache
mod_proxy_balancer. It seems that I’d have to manually change the
configuration file and restart apache whenever I add/remove a new
mongrel.

Well, you could write a script to edit the config for you and send
apache a usr1 signal ( “kill -usr1 [pid]” ) to cause it to reload the
updated config, then trigger the script whenever a new EC2 instance is
started or stopped.

Another approach could be to proxy everything to swiftiply (
http://swiftiply.swiftcore.org/ ), and have each new EC2 instances
mongrels register/deregister with the swiftiply proxy.

Yet another option would be to use switchpipe ( http://switchpipe.org/
) to manage things.

I haven’t done any of these, of course, so I’m basically talking
through my hat, but they all sound plausible!

Good luck

David

3

On Tue, 2008-02-19 at 01:41 +0100, Yaxm Y. wrote:

Is there a way to dynamically add/remove mongrel instances from Apache
mod_proxy_balancer. It seems that I’d have to manually change the
configuration file and restart apache whenever I add/remove a new
mongrel.

mod_proxy_balancer comes with the “balancer manager” with which can
toggle a member of the cluster offline and back online:

http://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html

You could script that interface and then call it from Capistrano. I
Googled around but couldn’t find an existing library for this… kind of
surprising. Maybe most folks are just going the “rewriting the config
file and send USR1” route.

Yours,

Tom

4

On Feb 19, 10:05 am, digitalronin [email protected] wrote:

Is there a way to dynamically add/remove mongrel instances from Apache
mod_proxy_balancer. It seems that I’d have to manually change the
configuration file and restart apache whenever I add/remove a new
mongrel.

[snip]

Yet another option would be to use switchpipe (http://switchpipe.org/
) to manage things.

Yep, that’s exactly what SwitchPipe does. Dynamically launches,
manages, and kills backend processes that speak HTTP. Even better than
that, it’ll kill Mongrels that aren’t in use for a certain period of
time… so rather than having, say, 3 Mongrels running ALL the time on
a quiet app, it’ll scale it back to zero Mongrels after X seconds of
inactivity if you like. Alternatively you can make it keep 1 Mongrel
up to pick up requests before scaling up to meet demand. Whatever you
want to do, it does it.

Cheers,
Peter C.
http://www.petercooper.co.uk/

5

While dorking around, I found you can disable/enable mongrel instances
in apache via curl. I added these two functions to my mongrel init
file:

enable_mongrel ()
{
curl -s -o /dev/null
http://127.0.0.1:8888/balancer-manager\?b=mongrel_cluster\&w=http://127.0.0.1:$1\&dw\=ENABLE
}

disable_mongrel ()
{
curl -s -o /dev/null
http://127.0.0.1:8888/balancer-manager\?b=mongrel_cluster\&w=http://127.0.0.1:$1\&dw\=DISABLE
}

in the case statement:

enable)
  enable_mongrel $2
  RETVAL=$?

;;
disable)
disable_mongrel $2
RETVAL=$?
;;

They accept the port number as an option. I use this as part of my
monit system to keep things in check. I have a very high traffic site
and I found proxy_balancer didn’t react quick enough.

usage:

service monit disable 8081
service monit enable 8081