Autoscaling on EC2 with Rails & Capistrano Deployments

Question

Is there a common strategy for setting up scripts on autoscaling to update the code in a capistrano deploy hierarchy to pull from your repository when the AMI is launched on an autoscaling event to ensure the commit running on the autoscaling machine matches the commit on non-autoscaling instances?

Answer 1

I run a setup a bit like this. I chose not to set instances to interact with git when they're booted because:

• I want instances to come up fast (deploy + bundle install can take a while)
• I want scaling up/replacing an instance to not depend on GitHub, rubygems etc
• I want scaling up an instance to be really simple

What I do is that the app I deploy is at /var/www/myapp. This is actually a separate EBS volume, mounted at that location. The filesystem is xfs because you can use xfs_freeze to safely take ebs snapshots of a mounted volume

When the deploy is done, in a capistrano after hook I snapshot the /var/www/myapp volume. I then update the block device mapping of the autoscaling launch configuration to say "when you start an instance, create a new volume from the snapshot and attach it to /dev/sdf.

All the instance has to do on startup is mount that device at /var/www/myapp, either by editing /etc/fstab or by running a super simple boot time script. Bundler is set to save its gems in /var/www/myapp/shared so the gems are taken care of too

Answer 2

Just in case anyone falls here, I've just discovered this gem:

https://github.com/lserman/capistrano-elbas

which will (as stated in the Readme):

• Deploy your code to each running instance connected to a given AutoScale group
• After deployment, create an AMI from one of the running instances
• Attach the AMI with the new code to a new AWS Launch Configuration
• Update your AutoScale group to use the new launch configuration
• Delete any old AMIs created by ELBAS
• Delete any old launch configurations created by ELBAS

So it ensures all instances of the autoscaling group (those running and those future) will run the same code.

Hope this helps