MonthMarch 2008

Update your rails application without downtime

It’s often not possible or wanted to take down your rails application for updates. Even if it is, I still regard downtime as something that should be avoided if possible.

When using the absolutely fantastic HAProxy to load-balance between your mongrels, you can take down a mongrel process without any adverse effects. When a mongrel process is not answering anymore, HAProxy just forwards the request to the next available mongrel and no harm is done.

So all you need is a way to stop and restart each mongrel, one after the other. I cooked up a bash script to do this. It’s not perfect, but I’ve been using it on several projects. The script stops each mongrel, waits until it’s really stopped, then restarts and checks if it’s really running.

Why a bash script ? I wanted to sharpen my (limited) bash scripting skills (so if you have any tips: feel free to comment).

Customize where needed. (properly indented version here)

If you are running monit, remember to ‘unmonitor’ before and ‘monitor’ after.


#!/usr/bin/env bash

#rails project home dir
#!!Change acc to your needs
cd /home/rails/le_test/current

#Ports mongrels are running on
#!!Change acc to your needs
for PORT in 8000 8001 8002
do
#the location of our pid-files
#!!Change acc to your needs
PF=/var/run/mongrel/mongrel.$PORT.pid

#pidfile exists ?
if [ -e $PF ]; then
PR=$(cat $PF)

#process still running ?
if ps $PR > /dev/null 2>&1; then
echo "$PF $PR Running - killing"
kill $PR
while ps $PR > /dev/null 2>&1; do
echo "$PR still running"
sleep 1
done
echo "$PR killed"
else
echo "$PF $PR Not Running - deleting pidfile"
rm -f $PF
fi
else
echo "$PF does not exist"
fi

#check if a command containing $PORT.pid is still running
#in case process is still active but pidfile was not found
if ps ax|grep $PORT.[p]id > /dev/null 2>&1; then
echo "!!! But process containing $PORT.pid running !!!"
echo "!!! NOT auto-restarting, Manual intervention necessary !!!"
else
echo "Restarting port $PORT"
#mongrel start cmd
#!!Change acc to your needs
mongrel_rails start -d -e production -p $PORT -P $PF
sleep 1
#check if process is actually running now (could also be done by pidfile based check)
while ! ps ax|grep $PORT.[p]id > /dev/null 2>&1; do
echo "Not Running"
done
fi

done

This should work with other load-balancers too, but since HAProxy had all features I expected to find and is very resource friendly and has a tiny footprint (and irons a shirt in 2 mins), I didn’t look any further (after looking at Pound, which only advantage is that it’s easy to install/configure and cisco css switches which are just a tiny bit expensive for my needs)

Quiet 2007

Ok, 2007 was a bit quiet on the blogging side. Been squeezing the max out of every minute of spare time and been working/learning as hell. Maybe more about what I’ve been upto later.

The layout started looking a bit stale so I modded a layout I like (credits: see bottom of page) to something I like even more (gustibus and stuff) and gave WP the much needed update. So there, giving a reason to unsubscribe to the 3 people that had forgotten that they were following my feed!

CSSVista: Internet Explorer Live CSS Editing

This tool has been around for quite some time, but it often surprises me how few people (also ‘professional’ ones) seem to have heard about it. Since it’s the only FREE live CSS IE editing tool I know, and since (added bonus!) it actually offers split-view Firefox/Internet Explorer editing, there’s no harm in spreading the word a bit.

Get it at: http://litmusapp.com/labs. DL link is sent to email address provided. However, I’m pretty sure they honour their no-spam policy.

Oh yes… it only runs on windows. But since there’s no escape having to consider IE users browsing your site, it’s almost worth keeping a windows installation for (that, and homebanking).

Tip: If your site requires a login and you have problems logging in using CSSVista: save the page you want to edit using Firefox and open it in CSSVista for editing.

And just in case you’ve been hiding under a rock, for day-to-day live CSS editing use (running fine under Linux!) there’s the webdev swiss army knife: Chris Pederick Web Developer Extension.