Illumina Innovates with Rancher and Kubernetes
There are three roles that can be assigned to nodes: etcd, controlplane and worker.
When designing your cluster(s), you have two options:
In either case, the worker role should not be used or added to nodes with the etcd or controlplane role.
Therefore, each node should have one of the following role configurations:
The cluster should have:
For more information on what each role is used for, refer to the section on roles for nodes in Kubernetes.
Adding more than one node with the controlplane role makes every master component highly available.
The number of nodes that you can lose at once while maintaining cluster availability is determined by the number of nodes assigned the etcd role. For a cluster with n members, the minimum is (n/2)+1. Therefore, we recommend creating an etcd node in 3 different availability zones within a region to survive the loss of one availability zone. If you use only two zones, you can only survive the loss of the zone where you don’t lose the majority of nodes.
Adding more than one node with the worker role will make sure your workloads can be rescheduled if a node fails.
You may have noticed that our High Availability (HA) Install instructions do not meet our definition of a production-ready cluster, as there are no dedicated nodes for the worker role. However, for your Rancher installation, this three node cluster is valid, because: