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Additional K8s Resources

Kubespray Hosts.Yaml Examples

Hosts.Yaml Overview

The Kubespray hosts.yaml inventory file is composed of 3 groups:

  • kube_node: list of Kubernetes nodes where the pods will run.
  • kube_control_plane: list of servers where Kubernetes control plane components (apiserver, scheduler, controller) will run.
  • etcd: list of servers to compose the etcd server. You should have at least 3 servers for failover purpose.

Please following these links for YAML examples and depending on your preferred topology:

All-In-One Node

Topology

  • node1 - is a single control plane + etcd node
  • node1 - is also running the pods

Pros

  • Easy to manage

Cons

  • Single point of failure for K8s/etcd/pods;
  • Thinner security barrier since pods are running on control plane / etcd nodes;

Example Hosts.yaml File

children:
kube_control_plane:
hosts:
node1:
kube_node:
hosts:
node1:
etcd:
hosts:
node1:
k8s_cluster:
children:
kube_control_plane:
kube_node:
calico_rr:
hosts: {}

One Control Plane Node with Multiple Worker Nodes

Topology

  • node1 - single control plane + etcd node
  • node2..N - kube nodes where the pods will run

Pros

  • Better security barrier since pods aren’t running on control plane / etcd nodes
  • Can scale by adding either more control plane nodes or worker nodes

Cons

  • Single point of failure only for K8s/etcd but not the pods

Example Hosts.yaml File

children:
kube_control_plane:
hosts:
node1:
kube_node:
hosts:
node2:
node3:
etcd:
hosts:
node1:
k8s_cluster:
children:
kube_control_plane:
kube_node:
calico_rr:
hosts: {}

Multiple Control Plane Nodes with Multiple Work Nodes

Topology

  • Nodes 1.-3 - the control plane + etcd nodes; (This makes K8s High Available)
  • Node 4.-N - the kube nodes on which the Pods will run

Pros

  • Highly available control plane / etcd
  • Better security barrier since pods aren’t running on control plane / etcd nodes
  • Can scale by adding either more control plane nodes or worker nodes

Cons

  • More complex environment makes its configuration & management more difficult

Example Hosts.yaml File

children:
kube_control_plane:
hosts:
node1:
node2:
node3:
kube_node:
hosts:
node4:
node5:
node6:
etcd:
hosts:
node1:
node2:
node3:
k8s_cluster:
children:
kube_control_plane:
kube_node:
calico_rr:
hosts: {}
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