Bootstrapping Salt on Linux EC2 with Cloud-Init

Salt is a great tool for remote execution and configuration management, however you will still need to bootstrap the daemon when spinning up a new node. One option is to create and save a custom AMI, but this creates another resource to maintain and document.

A better method for Linux machines uses Canonical's CloudInit to run a bootstrap script during an EC2 Instance initialization. Cloud-init takes the user_data string passed into a new AWS instance and runs it in a manner similar to rc.local. The bootstrap script needs to:

1. Install Salt with dependencies
2. Point the minion to the master

Here is a sample script:

#!/bin/bash

# Install saltstack
add-apt-repository ppa:saltstack/salt -y
apt-get update -y
apt-get install salt-minion -y
apt-get install salt-master -y
apt-get upgrade -y

# Set salt master location and start minion
sed -i 's/#master: salt/master: [salt_master_fqdn]/' /etc/salt/minion
salt-minion -d

First the script adds the saltstack ppa and installs the package. Then we copy over the minion config template and tell it where to find the master. You will have to replace [salt_master_fqdn] with something that resolves to your Salt master.

Used With Boto

Boto will accept a string for user data which can be used to pass our bootstrap script. If the script is saved to a file, you can read it into a string:

import boto

user_data = open('salt_bootstrap.sh')

conn = boto.connect_ec2(<AWS_ACCESS_ID>, <AWS_SECRET_KEY>)

reservation = conn.run_instances(image_id=<ami_id>,
                                 key_name=<key_name>,
                                 user_data=user_data.read())

Additional Notes

Sometime in the future the ppa will include and install an upstart file. In the meantime, you can use the bootstrap to build one.

It may also be useful to set the node's role during this phase. One option would be saving the node's role to a file and then using a custom Grain to select it.