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:

• Kubespray Hosts.Yaml Examples
  • Hosts.Yaml Overview
• All-In-One Node
  • Topology
  • Pros
  • Cons
  • Example Hosts.yaml File
• One Control Plane Node with Multiple Worker Nodes
  • Topology
  • Pros
  • Cons
  • Example Hosts.yaml File
• Multiple Control Plane Nodes with Multiple Work Nodes
  • Topology
  • Pros
  • Cons
  • Example Hosts.yaml File

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: {}