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Creating and bootstrapping EC2 instances in an Amazon VPC using Chef & Knife

Instances in an Amazon VPC are a little tricker than usual to create using the knife ec2 server create command, because they are, of course, private. However, if you have an SSH gateway you can use that to create and bootstrap them.

There is one small caveat, however: if you create a server in a public subnet, it will not be able to access the Internet (and thus complete the Chef bootstrap process) until you assign it an Elastic IP. The knife ec2 plugin doesn’t let you do this, so you’ll either have to do it manually after the server has been created, or script it using the AWS API.

Creating a server

You’ll need:

  • an SSH gateway in the VPC, accessible from the Internet
    • you should have a user account on this gateway, preferably with public key authentication
  • the ID of the subnet you intend to deploy into
  • the AMI you wish to use
  • the security group IDs for the new instance
    • one of these must contain a rule which allows inbound SSH access from the SSH gateway

If you have all that, you can use the following command. It’s a bit of a mouthful:

knife ec2 server create
  --image ami-ce7b6fba
  --flavor m1.small
  --region eu-west-1
  --server-connect-attribute private_ip_address
  --ssh-gateway [email protected]
  --ssh-user ubuntu
  --identity-file ~/.ssh/clarkdave.pem
  --subnet subnet-8d034be5
  --environment production
  --node-name web1
  --run-list 'role[base],role[web_server]'

To explain a few of the arguments:

  • --server-connect-attribute: after the instance is created, Knife will use this attribute to find an IP address to connect to. Because VPC instances don’t have a public IP by default, we use the private_ip_address instead
  • --ssh-gateway: don’t forget to specify the user (e.g. [email protected]…), or everything could fail with unhelpful errors
    • I have only tested this with a user who has public key authentication. The command may not be smart enough to prompt for a password for the SSH gateway, so if it fails, that could be why
  • --ssh-user: this is the user Chef will connect with to bootstrap the new instance. For Amazon AMI’s it’s usually ec2-user

Assuming all the options were correct, Chef should now create and then proceed to bootstrap the server. As I mentioned in the intro, if this server is in a public subnet, you’ll need to give it an Elastic IP because the bootstrap can proceed (it will just sit there timing out otherwise, while it attempts to download Chef).

Bootstrapping a server

If you already have a server in the VPC, you can also bootstrap it using the SSH gateway:

knife bootstrap 10.0.10.245
  --ssh-gateway [email protected]
  --ssh-user ubuntu
  --sudo
  --identity-file ~/.ssh/clarkdave.pem
  --environment production
  --node-name web1
  --run-list 'role[base],role[web_server]'

And that’s all there is to it!

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