From f5a6234ef4cbc2896e09100c7f0662dcb2117374 Mon Sep 17 00:00:00 2001
From: marcel-dempers <aimvec@gmail.com>
Date: Wed, 11 Oct 2023 16:40:42 +1100
Subject: [PATCH] affinity updates

---
 kubernetes/affinity/README.md          | 31 +++++++++++++++++++++++++-
 kubernetes/affinity/kind.yaml          |  8 +++----
 kubernetes/affinity/node-affinity.yaml |  9 ++++++++
 kubernetes/affinity/pod-affinity.yaml  | 16 ++++++-------
 4 files changed, 51 insertions(+), 13 deletions(-)

diff --git a/kubernetes/affinity/README.md b/kubernetes/affinity/README.md
index 55d9fdc..5a2b08e 100644
--- a/kubernetes/affinity/README.md
+++ b/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
+```
+
diff --git a/kubernetes/affinity/kind.yaml b/kubernetes/affinity/kind.yaml
index d0b17f8..c1306d4 100644
--- a/kubernetes/affinity/kind.yaml
+++ b/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
diff --git a/kubernetes/affinity/node-affinity.yaml b/kubernetes/affinity/node-affinity.yaml
index 6870f6a..037ce9d 100644
--- a/kubernetes/affinity/node-affinity.yaml
+++ b/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:
diff --git a/kubernetes/affinity/pod-affinity.yaml b/kubernetes/affinity/pod-affinity.yaml
index 9a8abfc..1bccf3d 100644
--- a/kubernetes/affinity/pod-affinity.yaml
+++ b/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
-            topologyKey: zone
\ No newline at end of file
+                - app-disk
+            topologyKey: "kubernetes.io/hostname"
\ No newline at end of file