The Installation Process Details
Because each machine in the cluster requires information about the cluster when it is provisioned, OKD uses a temporary bootstrap machine during initial configuration to provide the required information to the permanent control plane. It boots by using an Ignition config file that describes how to create the cluster. The bootstrap machine creates the master machines that make up the control plane. The control plane machines then create the compute machines, which are also known as worker machines. The following figure illustrates this process:
After the cluster machines initialize, the bootstrap machine is destroyed. All clusters use the bootstrap process to initialize the cluster, but if you provision the infrastructure for your cluster, you must complete many of the steps manually.
Bootstrapping a cluster involves the following steps:
- The bootstrap machine boots and starts hosting the remote resources required for the control plane machines to boot. (Requires manual intervention if you provision the infrastructure)
- The bootstrap machine starts a single-node etcd cluster and a temporary Kubernetes control plane.
- The control plane machines fetch the remote resources from the bootstrap machine and finish booting. (Requires manual intervention if you provision the infrastructure)
- The temporary control plane schedules the production control plane to the production control plane machines.
- The Cluster Version Operator (CVO) comes online and installs the etcd Operator. The etcd Operator scales up etcd on all control plane nodes.
- The temporary control plane shuts down and passes control to the production control plane.
- The bootstrap machine injects OKD components into the production control plane.
- The installation program shuts down the bootstrap machine. (Requires manual intervention if you provision the infrastructure)
- The control plane sets up the worker nodes.
- The control plane installs additional services in the form of a set of Operators.
The result of this bootstrapping process is a fully running OKD cluster. The cluster then downloads and configures remaining components needed for the day-to-day operation, including the creation of worker machines in supported environments.