Why do you need Node Affinity?
Node Affinity
nodeSelector is not enough to set PODs on the specific Node.
If you want to make some limitations that are more complex than nodeSelector, you have to use affinity.
Compare nodeSelector and affinity
nodeSelctor node-selector.yml
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| apiVersion: v1
kind: Pod
metadata:
name: myapp-pod
spec:
containers:
- name: nginx
image: nginx
nodeSelector:
size: Large
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affinity affinity.yml
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| apiVersion: v1
kind: Pod
metadata:
name: myapp-pod
spec:
containers:
- name: nginx
image: nginx
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: size
operator: In
values:
- Large
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affinity Types
DuringScheduling
The meaning of schedule is to bind the POD to the Node in Kubernetes.
So DuringScheduling means “How to apply when it’s binding”.
DuringExecution
DuringExecution means “Hwo to apply to the running PODs”.
| Type | Action |
|---|
required | Apply the Configuration |
preferred | Try to apply, but it’s not necessary |
ignore | No Action |
operator Types in affinity
| Type | Action |
|---|
| In | It is like ‘IN’ in SQL. The values is an array. |
| NotIn | It is like NOT IN in SQL. The values is an array. |
| Exists | Just check the key is exists. The values is not defined. |
Examples of affinity
Scenarios
There are three Nodes.
Each node has a label that key is ‘size’.
The labels are Large, Medium, and Small.
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| # Large on node01
kubectl label nodes node01 size=Large
# Medium on node02
kubectl label nodes node02 size=Medium
# Small on node03
kubectl label nodes node03 size=Small
# Check labels
kubectl get nodes --show-labels
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Scheduling PODs to Large Node
Use nodeSelector
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| apiVersion: v1
kind: Pod
metadata:
name: myapp-pod
spec:
containers:
- name: nginx-container
image: nginx
nodeSelector: Large
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Use affinity
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| apiVersion: v1
kind: Pod
metadata:
name: myapp-pod
spec:
containers:
- name: nginx-container
image: nginx
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: size
operator: In
values:
- Large
|
Scheduling PODs not to Small Node
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| apiVersion: v1
kind: Pod
metadata:
name: myapp-pod
spec:
containers:
- name: nginx-container
image: nginx
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: size
operator: NotIn
values:
- Small
|
Scheduling PODs to Medium and Small Node
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| apiVersion: v1
kind: Pod
metadata:
name: myapp-pod
spec:
containers:
- name: nginx-container
image: nginx
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: size
operator: In
values:
- Medinum
- Small
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Deployment with affinity
blue-deployment.yml
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| apiVersion: apps/v1
kind: Deployment
metadata:
name: blue
spec:
template:
metadata:
name: blue-pod
labels:
app: blue-app
spec:
containers:
- name: nginx-container
image: nginx
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: color
operator: In
values:
- blue
replicas: 3
selector:
matchLabels:
app: blue-app
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red-deployment.yml
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| apiVersion: apps/v1
kind: Deployment
metadata:
name: red
spec:
replicas: 2
selector:
matchLabels:
app: red-app
template:
metadata:
name: red-pod
labels:
app: red-app
spec:
containers:
- name: nginx-container
image: nginx
affinity:
nodeAffinity:
requiredDuringSchedulingIgnoredDuringExecution:
nodeSelectorTerms:
- matchExpressions:
- key: node-role.kubernetes.io/master
operator: Exists
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