I Recently stumbled across a predicament of multiple aws accounts.
This is a minor predicament but a predicament nonethless.
I have a situation where i have

1. A personal AWS account

2. A work AWS account

3. A vendor AWS account

These three AWS accounts all use the same chef-server. So to make my life easier i decided to organize them.
I created the following structure:

$ mkdir -p ~/chef-aws/{personal,work,thirdparty}/.chef

I copied my knife.rb from ~/.chef/knife.rb into each of these folders.

$ cp -p ~/.chef/knife.rb ~/chef-aws/personal
$ cp -p ~/.chef/knife.rb ~/chef-aws/work
$ cp -p ~/.chef/knife.rb ~/chef-aws/thirdparty

Here’s an example of the knife.rb file
You can find details on setting up knife with ec2 here : Knife-EC2 Configuration

current_dir = File.dirname(__FILE__)
log_level                :info
log_location             STDOUT
node_name                "neosirex"
client_key               "/home/James/.chef/myuser.pem"
validation_client_name   "neosirex-validator"
validation_key           "/home/James/.chef/random-validator.pem"
chef_server_url          "https://api.opscode.com/organizations/somemakebelieveaccount"
cache_type               'BasicFile'
cache_options( :path => "#{ENV['HOME']}/.chef/checksums" )
cookbook_path            ["#{current_dir}/../cookbooks"]

Here’s the snippet that’s added to each AWS specific knife.rb

knife[:aws_access_key_id] ='< AWS ACCESS KEY GOES HERE >'
knife[:aws_secret_access_key] ='< AWS SECRET KEY GOES HERE >'

So now in order to use different AWS accounts what i do is change into each of those aws directories and run knife commands from there.
Each of the following commands would give me the output only of the relevant AWS server

$ cd ~/chef-aws/personal && knife ec2 server list
$ cd ~/chef-aws/work && knife ec2 server list
$ cd ~/chef-aws/thirdparty && knife ec2 server list

I Leave my default ~/.chef/knife.rb file without AWS credentials in it.
This is because i don’t want to accidently deploy to the wrong AWS account.
There’s still room for human error but i suppose it’s better than nothing
If someone has a better approach to this i’d like to know about it.