Taints and Tolerations

Used to set restrictions on what pods can be shceduled on which nodes

Default there are none and the schedule will schedule pods in a balanced way across the nodes

Taints

Set on Nodes

Lets say there are 3 nodes with a taints

Node	Taint
node-1	Red
node-2	Green
node-3	Blue

Tolerations

Set on Pods

Lets say there are pods with tolerations

Pod	Toleration
pod-1	Blue
pod-2	Green
pod-3	Red
pod-4	Red
pod-5	Red
pod-7	Blue

Kube scheduler will now deploy the pods and add them to the resulting nodes

Node-1 RED
pod-3
pod-4
pod-5

Node-2 GREEN
pod-2

Node-3 BLUE
pod-1
pod-7

How to Taint a node

1kubectl taint nodes node-name key=value:taint-effect

rm taint

1kubectl taint nodes node-name key=value:taint-effect-

Taint effect

This is what will happen if the Pod DOES NOT TOLERATE the taint

NoSchedule - will not be scheduled on node
PreferNoSchedule - will try to prevent scheduling on node
NoExecute - new pods wont be sheduled and existing bods will be removed that do not tolerate the taint

Add Tolerations to Pod

1spec:
2  tolerations: # Must be in " quotes "
3    - key: "app"
4      operator: "Equal"
5      value: "blue"
6      effect: Taint Effect

Example

 1apiVersion: 
 2kind: Pod
 3metadata:
 4  name: simple-webapp-color
 5spec:
 6  tolerations: # Must be in " quotes "
 7    - key: "app"
 8      operator: "Equal"
 9      value: "blue"
10      effect: "NoSchedule"
11  
12  containers:
13    - name: simple-webapp-color
14      image: simple-webapp-color
15      ports:
16        - containerPort: 8080
17      envFrom:
18        - configMapRef:
19            name: app-config

Master Node

Master node has a default taint

Best practice to not deploy application workloads on master node

1kubectl describe node kubemaster | grep Taint

output

1Taints:            node-role.kubernetes.io/master:NoShcedule