Poor Man’s Automated Snapshots for EC2

doegox

We’ve invested quite some time in our WordPress Micro instance now. It’s definitely past the playing-around, prototype phase, so let’s get some automated backups in place. But, since we already suffered to get the EC2 API Tools installed, the hard part is actually done. Let’s get a couple of weekly cronjobs setup:

bitnami@awo:~$ crontab -l
# m h  dom mon dow   command
12 01 * * 6 /bin/bash /home/bitnami/scripts/createSnapshot.sh >/tmp/createSnapshot.log 2>&1
22 01 * * 6 /bin/bash /home/bitnami/scripts/deleteSnapshots.sh >/tmp/deleteSnapshots.log 2>&1

The time on a EC2 instance defaults to UTC – Greenwich, England.

As with most sysadmin tasks, there’s the right way to make system wide, consistent snapshots (with an XFS based EBS), and the easy way. As we can afford a minute a week with no writes, we take the easy way:

bitnami@awo:$ less /home/bitnami/scripts/createSnapshot.sh
#!/bin/bash
export EC2_PRIVATE_KEY=/home/bitnami/.ec2/pk-*secret*.pem
export EC2_CERT=/home/bitnami/.ec2/cert-*secret*.pem
export JAVA_HOME=/usr/lib/jvm/java-6-openjdk/jre
sudo /opt/bitnami/ctlscript.sh stop mysql
ec2addsnap vol-96268afe -d "Weekly backup"
sleep 30
sudo /opt/bitnami/ctlscript.sh start mysql

The stop mysql is the uncool portion of this script. But, not doing this might give you a corrupt database snapshot (which you wouldn’t even learn about until after disaster struck). So, for the time it takes ec2addsnap to do its thing, database writes will fail. The time we’ve scheduled this means those writes are user comments. The sleep 30 is also little league. Better would be to capture the snapshot ID from the ec2addsnap command and wait for status ‘completed’ – check the bottom of that post for some starter code.

Cleaning up EC2 snapshots

Running a backup once a week creates ~52 snapshots a year – not too bad. If you decide to run daily (or even hourly), these snapshots will pile up quickly.

bitnami@awo:$ less /home/bitnami/scripts/deleteSnapshots.sh
#!/bin/bash
export EC2_PRIVATE_KEY=/home/bitnami/.ec2/pk-*secret*.pem
export EC2_CERT=/home/bitnami/.ec2/cert-*secret*.pem
export JAVA_HOME=/usr/lib/jvm/java-6-openjdk/jre
ec2-describe-snapshots | sort -r -k 5 | grep "Weekly backup" | sed 1,6d | awk '{print "Deleting snapshot: " $2}; system("ec2-delete-snapshot " $2)'

The sort -r -k 5 gives us descending sort by snapshot date, and the sed 1,6d skips the first 6 in the list so that ec2-delete-snapshot gets called on the 7th (and oldest) snapshot. Naturally, you only want to delete your “Weekly backups”, thus the corresponding grep.

I hope you’re having fun running your own instance in the cloud. The fact that Amazon gives this to us for nothing for an entire year just convinces me more of the marketing genius employed there. After a year of this “geek crack”, who could possibly go cold turkey?

Professional Grade Virtual Computing for “Free”

In case you missed my other posts on acquiring, maintaining, backing-up and monitoring your virtual server, here’s the complete list:
• EC2 setup : Migrate Your WordPress Blog to a Bitnami EC2 Instance
• Performance : WordPress Caching For High Performance EC2 Micro Instances
• Monitoring : Cloudkick Monitoring for EC2