Public and Private Keys

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Every request made by the chef-client to the Chef server must be an authenticated request using the Chef server API and a private key. When the chef-client makes a request to the Chef server, the chef-client authenticates each request using a private key located in /etc/chef/client.pem.

How are Keys Used?

The authentication process ensures the Chef server responds only to requests made by trusted users. Public key encryption is used by the Chef server. When a node and/or a workstation is configured to run the chef-client, both public and private keys are created. The public key is stored on the Chef server, while the private key is returned to the user for safe keeping. (The private key is a .pem file located in the .chef directory or in /etc/chef.)

Both the chef-client and knife use the Chef server API when communicating with the Chef server. The chef-validator uses the Chef server API, but only during the first chef-client run on a node.

Each request to the Chef server from those executables sign a special group of HTTP headers with the private key. The Chef server then uses the public key to verify the headers and verify the contents.

chef-client

RSA public key-pairs are used to authenticate the chef-client with the Chef server every time a chef-client needs access to data that is stored on the Chef server. This prevents any node from accessing data that it shouldn’t and it ensures that only nodes that are properly registered with the Chef server can be managed.

Knife

RSA public key-pairs are used to authenticate knife with the Chef server every time knife attempts to access the Chef server. This ensures that each instance of knife is properly registered with the Chef server and that only trusted users can make changes to the data.

knife can also use the knife exec subcommand to make specific, authenticated requests to the Chef server. knife plugins can also make authenticated requests to the Chef server by leveraging the knife exec subcommand.

chef-validator

However, during the first chef-client run, this private key does not exist. Instead, the chef-client will attempt to use the private key assigned to the chef-validator, located in /etc/chef/validation.pem. (If, for any reason, the chef-validator is unable to make an authenticated request to the Chef server, the initial chef-client run will fail.)

During the initial chef-client run, the chef-client will register with the Chef server using the private key assigned to the chef-validator, after which the chef-client will obtain a client.pem private key for all future authentication requests to the Chef server.

After the initial chef-client run has completed successfully, the chef-validator is no longer required and may be deleted from the node. Use the delete_validation recipe found in the chef-client cookbook (https://github.com/chef-cookbooks/chef-client) to remove the chef-validator.

Where are Keys Stored?

Keys are stored in different locations, depending on if the location is a node or a workstation.

Nodes

Each node stores its private key locally. This private key is generated as part of the bootstrap process that initially installs the chef-client on the node. The first time chef-client runs on that node, it uses the chef-validator to authenticate, but then on each subsequent run it uses the private key generated for that client by the Chef server.

Workstations

Each workstation stores its private key in the chef-repo. This private key is generated by the Chef server and must be download from the server and copied to the .chef directory in the chef-repo. If a new private key is required, simply regenerate it from the Chef server and re-copy it to the chef-repo.

The chef-repo is a directory on your workstation that stores:

  • Cookbooks (including recipes, attributes, custom resources, libraries, and templates)
  • Roles
  • Data bags
  • Environments

The chef-repo directory should be synchronized with a version control system, such as git. All of the data in the chef-repo should be treated like source code.

knife is used to upload data to the Chef server from the chef-repo directory. Once uploaded, that data is used by the chef-client to manage all of the nodes that are registered with the Chef server and to ensure that the correct cookbooks, environments, roles, and other settings are applied to nodes correctly.

The .chef directory is a hidden directory that is used to store validation key files and the knife.rb file.

Generating Keys

The Chef server generates two types of private keys: one for nodes and workstations (typically referred to as a “client key”) and the other for the organization. If (for any reason) a new key is required, the Chef server can re-generate these keys.