affinity updates

kubernetes/affinity/README.md

@@ -22,7 +22,7 @@ demo-worker3         Ready    <none>          35s   v1.28.0
 
 ## Node Affinity 
 
-[Node Affinity](https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#node-affinity) is similar to `nodeSelector` however you can define more complex expressions
+[Node Affinity](https://kubernetes.io/docs/concepts/scheduling-eviction/assign-pod-node/#node-affinity) is similar to `nodeSelector` however you can define more complex expressions. "Like my pods must run on SSD nodes or preffer SSD nodes"
 
 For example: 
 * Node selector is a hard and fast rule meaning a pod will not be scheduled if the selection is not satisfied
@@ -59,5 +59,34 @@ kubectl taint nodes demo-worker type=ssd:NoSchedule-
 kubectl taint nodes demo-worker3 type=ssd:NoSchedule-
 ```
 
+## Pod Affinity 
 
 
+```
+kubectl apply -f app-disk --replicas 3
+kubectl apply -f web-disk --replicas 3
+```
+
+## Pod Anti-Affinity
+
+Let's say we observe our `app-disk` application disk usage is quite intense, and we would like to prevent `app-disk` pods from running together. </br>
+This is where anti-affinity comes in:
+
+```
+podAntiAffinity:
+  requiredDuringSchedulingIgnoredDuringExecution:
+  - labelSelector:
+      matchExpressions:
+      - key: app
+        operator: In
+        values:
+        - app-disk
+    topologyKey: "kubernetes.io/hostname"
+```
+
+After applying the above, we can roll it out:
+
+```
+kubectl apply -f node-affinity.yaml
+```
+

kubernetes/affinity/kind.yaml

@@ -2,17 +2,17 @@ kind: Cluster
 apiVersion: kind.x-k8s.io/v1alpha4
 nodes:
 - role: control-plane
-- role: worker
+- role: worker  #demo-worker
   labels:
     zone: us-east
     type: ssd
-- role: worker
+- role: worker  #demo-worker2
   labels:
     zone: us-west
     type: ssd
-- role: worker
+- role: worker  #demo-worker3
   labels:
     zone: us-east
-- role: worker
+- role: worker  #demo-worker4
   labels:
     zone: us-west

kubernetes/affinity/node-affinity.yaml

@@ -19,6 +19,15 @@ spec:
       - name: app-disk
         image: nginx:latest
       affinity:
+        podAntiAffinity:
+          requiredDuringSchedulingIgnoredDuringExecution:
+          - labelSelector:
+              matchExpressions:
+              - key: app
+                operator: In
+                values:
+                - app-disk
+            topologyKey: "kubernetes.io/hostname"
         nodeAffinity:
           requiredDuringSchedulingIgnoredDuringExecution:
             nodeSelectorTerms:

kubernetes/affinity/pod-affinity.yaml

@@ -2,29 +2,29 @@
 apiVersion: apps/v1
 kind: Deployment
 metadata:
-  name: app-disk2
+  name: web-disk
   labels:
-    app: app-disk2
+    app: web-disk
 spec:
   selector:
     matchLabels:
-      app: app-disk2
+      app: web-disk
   replicas: 1
   template:
     metadata:
       labels:
-        app: app-disk2
+        app: web-disk
     spec:
       containers:
-      - name: app-disk2
+      - name: web-disk
         image: nginx:latest
       affinity:
         podAffinity:
           requiredDuringSchedulingIgnoredDuringExecution:
           - labelSelector:
               matchExpressions:
-              - key: zone
+              - key: app
                 operator: In
                 values:
-                - us-east
+                - app-disk
-            topologyKey: zone
+            topologyKey: "kubernetes.io/hostname"