Bootstrap is the PROCESS by which the Chef Client is INSTALLED on the Chef nodes. Chef nodes could be physical, virtual or cloud machine. The bootstrap process can be done in TWO ways:

1. Using the “knife bootstrap” sub-command

The “knife bootstrap” command is issued from the Chef workstation. The command first creates an SSH connection with the NODE then installs the Chef Client along with all its dependencies on the node. This command also generates keys and register the node with Chef Server. In earlier versions of Chef Client, "ORGANIZATION-validator.pem" file was used to authenticate the Chef node with the Chef Server during the first Chef Client run. Starting from Chef Client 12.1, "USER.pem" file could be used to authenticate the new Chef node. This process is also known as “validatorless bootstrap”.

1.  Manual install in the node directly

We need to login to the Chef node and manually install the chef-client. Once it’s installed we need to manually set up the connection with the Chef Server.

Unattended Installs are often done on Chef nodes created in AWS Auto SCALING, AWS CloudFormation, Rackspace Auto Scale, and PXE. Chef Client is installed without SSH connection on the Chef nodes.