Affinity and anti-affinity

README.md

-# scheduling
+# Scheduling
 
 Affinity/Anti-Affinity Rules, Taints and Tolerations
+
+## Index
+* [Affinity/Anti-Affinity Rules](#troubleshooting-and-debugging)
+  * [Exercise: Node Selector](#exercise-debugging-pods)
+  * [Exercise: Node Affinity](#exercise-events)
+  * [Exercise: Node Anti-Affinity](#exercise-debugging-services)
+* [Taints and Tolerations](#monitoring)
+  * [Exercise: Taints](#exercise-kubernetes-dashboard)
+  * [Exercise: Tolerations](#exercise-weave-scope)
+
+---
+
+## Affinity/Anti-Affinity Rules
+
+It is one way to set rules on which nodes are selected by the scheduler. This feature is a generalization of the nodeSelector feature. The rules are defined using the familiar concepts of custom labels on nodes and selectors specified in pods, and they can be either required or preferred, depending on how strictly you want the scheduler to enforce them.
+
+
+### Exercise: Node Selector
+
+1. First show your node labels.
+
+```
+$ kubectl get node --output=jsonpath={.items..metadata.labels}
+```
+> Output may different for each environments or cluster setup. This is how it look like in minikube
+
+__output__
+
+```
+map[beta.kubernetes.io/arch:amd64 beta.kubernetes.io/os:linux kubernetes.io/arch:amd64 kubernetes.io/hostname:minikube kubernetes.io/os:linux node-role.kubernetes.io/master:]
+```
+
+2. Create a pod with `nodeSelector` or use the `yaml` below.
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+ name: nginx
+ labels:
+   env: test
+spec:
+ containers:
+ - name: nginx
+   image: nginx:latest
+   imagePullPolicy: IfNotPresent
+ nodeSelector:
+   disktype: ssd
+```
+__Command__
+
+```
+$ kubectl apply -f yaml/node-selector.yaml 
+```
+
+3. List the pods
+
+```
+$ kubectl get pods
+```
+__Output__
+```
+NAME    READY   STATUS    RESTARTS   AGE
+nginx   0/1     Pending   0          59s
+```
+
+4. Pod is in `Pending` state. Describe the pod for more information about the status.
+
+```
+$ kubectl describe pod nginx
+```
+
+__Output__
+
+```
+Name:               nginx
+Namespace:          default
+Priority:           0
+PriorityClassName:  <none>
+Node:               <none>
+Labels:             env=test
+Annotations:        kubectl.kubernetes.io/last-applied-configuration:
+                      {"apiVersion":"v1","kind":"Pod","metadata":{"annotations":{},"labels":{"env":"test"},"name":"nginx","namespace":"default"},"spec":{"contai...
+Status:             Pending
+IP:                 
+Containers:
+  nginx:
+    Image:        nginx:latest
+    Port:         <none>
+    Host Port:    <none>
+    Environment:  <none>
+    Mounts:
+      /var/run/secrets/kubernetes.io/serviceaccount from default-token-6zm5t (ro)
+Conditions:
+  Type           Status
+  PodScheduled   False 
+Volumes:
+  default-token-6zm5t:
+    Type:        Secret (a volume populated by a Secret)
+    SecretName:  default-token-6zm5t
+    Optional:    false
+QoS Class:       BestEffort
+Node-Selectors:  disktype=ssd
+Tolerations:     node.kubernetes.io/not-ready:NoExecute for 300s
+                 node.kubernetes.io/unreachable:NoExecute for 300s
+Events:
+  Type     Reason            Age                  From               Message
+  ----     ------            ----                 ----               -------
+  Warning  FailedScheduling  64s (x3 over 2m26s)  default-scheduler  0/1 nodes are available: 1 node(s) didn't match node selector.
+```
+5. When you look the events, it cant be scheduled to the node because the node's labels does not match with `nodeSelector`. Label the node `disktype=ssd` and describe it again.
+
+>Your nodename can be different.
+
+```
+$ kubectl label node minikube disktype=ssd
+```
+
+6. List the pods.
+
+```
+$ kubectl get pods
+```
+
+__Expected output__
+
+```
+NAME    READY   STATUS    RESTARTS   AGE
+nginx   1/1     Running   0          6m13s
+```
+
+7. Clean up
+
+```
+$ kubectl delete pod nginx
+```
+
+---
+
+### Exercise: Node Affinity
+
+Node affinity is a set of rules used by the scheduler to determine where a pod can be placed.
+
+1. Create a pod with NodeAffinity for doing previous exercise with node affinity. Use the yaml below or `yaml/node-affinity-1.yaml`
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+ name: with-node-affinity
+spec:
+ affinity:
+   nodeAffinity:
+     requiredDuringSchedulingIgnoredDuringExecution:
+       nodeSelectorTerms:
+       - matchExpressions:
+         - key: "disktype"
+           operator: In
+           values: ["ssd"]
+ containers:
+ - name: with-node-affinity
+   image: nginx:latest
+```
+
+__Command__
+
+```
+$ kubectl apply -f yaml/node-affinity-1.yaml
+```
+
+> The operator represents the relationship between the label on the node and the set of values in the `matchExpression` parameters in the pod specification. 
+This value can be `In`, `NotIn`, `Exists`, or `DoesNotExist`, `Lt`, or `Gt`.
+
+
+2. The label will be found by the NodeAffinity because we labeled the our node in the previous exercise. List the pods.
+
+```
+$ kubectl get pods
+```
+
+__Expected Output__
+
+```
+NAME                 READY   STATUS    RESTARTS   AGE
+with-node-affinity   1/1     Running   0          4m40s
+```
+
+3. Lets delete the pod.
+
+```
+$ kubectl delete pod with-node-affinity
+```
+
+4. Create a pod with the yaml below or use `yaml/node-affinity-2.yaml`
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+ name: with-node-affinity
+spec:
+ affinity:
+  nodeAffinity:
+    preferredDuringSchedulingIgnoredDuringExecution:
+    - weight: 1
+      preference:
+        matchExpressions:
+        - key: "disktype"
+          operator: In
+          values:
+          - hdd
+ containers:
+ - name: with-node-affinity
+   image: nginx:latest
+```
+
+> As you realized the node affnity has `preferredDuringSchedulingIgnoredDuringExecution` field at this time. Preferred Rules mean that if nodes match the rules, they will be chosen first, and only if no preferred nodes are available will non-preferred nodes be chosen. 
+
+5. The other difference is the affinity looking for label `disktype=hdd` but as you remember we label the node with `disktype=ssd`. However, this affinity has a type `prefered` so the pod will e scheduled. Apply the yaml.
+
+```
+$ kubectl apply -f yaml/node-affinity-2.yaml
+```
+
+6. List the pods
+```
+$ kubectl get pods
+```
+
+__Expected output__
+
+```
+NAME                          READY   STATUS    RESTARTS   AGE
+with-node-affinity-prefered   1/1     Running   0          28s
+```
+
+> The behaviour of the affinity types;
+
+| AFFINITY SELECTOR                               | REQUIREMENTS MET | REQUIREMENTS NOT MET | REQUIREMENTS LOST |
+|-------------------------------------------------|------------------|----------------------|-------------------|
+| requiredDuringSchedulingIgnoredDuringExecution  | RUNS             | FAILS                | KEEPS RUNNING     |
+| preferredDuringSchedulingIgnoredDuringExecution | RUNS             | RUNS                 | KEEPS RUNNING     |
+
+> .
+
+---
+
+### Exercise: Node Anti-Affinity
+
+You can use `NotIn` and `DoesNotExist` to achieve node anti-affinity behavior.
+
+1. Create yaml file from the yalm below or use `yaml/node-anti-affinity.yaml`
+
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+ name: with-node-affinity
+spec:
+ affinity:
+   nodeAffinity:
+     requiredDuringSchedulingIgnoredDuringExecution:
+       nodeSelectorTerms:
+       - matchExpressions:
+         - key: "disktype"
+           operator: NotIn
+           values: ["hdd"]
+ containers:
+ - name: with-node-affinity
+   image: nginx:latest
+```
+
+__Command__
+
+```
+$ kubectl apply -f yaml/node-anti-affinity.yaml
+```
+
+> This pod is looking for a node that does not have `disktype` key equals to `hdd` value. Our node is still labeled with `disktype=ssd` so there will not be a problem.
+
+2. List the pods
+
+```
+$ kubectl get pods
+```
+__Expected Output__
+
+```
+NAME            READY   STATUS    RESTARTS   AGE
+anti-affinity   1/1     Running   0          7m1s
+```
+
+---
+
+## Taints and Tolerations
+
+You apply taints to a node through the node specification (NodeSpec) and apply tolerations to a pod through the pod specification (PodSpec). A taint on a node instructs the node to repel all pods that do not tolerate the taint.
+
+### Exercise: Taints
+
+
+
+### Exercise: Tolerations
\ No newline at end of file

yaml/node-affinity-1.yaml

+apiVersion: v1
+kind: Pod
+metadata:
+ name: with-node-affinity
+spec:
+ affinity:
+   nodeAffinity:
+     requiredDuringSchedulingIgnoredDuringExecution:
+       nodeSelectorTerms:
+       - matchExpressions:
+         - key: "disktype"
+           operator: In
+           values: ["ssd"]
+ containers:
+ - name: with-node-affinity
+   image: nginx:latest
\ No newline at end of file

yaml/node-affinity-2.yaml

+apiVersion: v1
+kind: Pod
+metadata:
+  name: with-node-affinity-prefered
+spec:
+ affinity:
+  nodeAffinity:
+    preferredDuringSchedulingIgnoredDuringExecution:
+    - weight: 1
+      preference:
+        matchExpressions:
+        - key: "disktype"
+          operator: In
+          values:
+          - hdd
+ containers:
+ - name: with-node-affinity
+   image: nginx:latest
+

yaml/node-anti-affinity.yaml

+apiVersion: v1
+kind: Pod
+metadata:
+ name: anti-affinity
+spec:
+ affinity:
+   nodeAffinity:
+     requiredDuringSchedulingIgnoredDuringExecution:
+       nodeSelectorTerms:
+       - matchExpressions:
+         - key: "disktype"
+           operator: NotIn
+           values: ["hdd"]
+ containers:
+ - name: with-node-affinity
+   image: nginx:latest
\ No newline at end of file

yaml/node-selector.yaml

+apiVersion: v1
+kind: Pod
+metadata:
+ name: nginx
+ labels:
+   env: test
+spec:
+ containers:
+ - name: nginx
+   image: nginx:latest
+   imagePullPolicy: IfNotPresent
+ nodeSelector:
+   disktype: ssd
+