Merge pull request #28434 from mehabhalodiya/fix-28324

Add tooltip for affinity

content/en/docs/reference/glossary/affinity.md

@@ -0,0 +1,22 @@
+---
+title: Affinity
+id: affinity
+date: 2019-01-11
+full_link: /docs/concepts/scheduling-eviction/assign-pod-node/#affinity-and-anti-affinity
+short_description: >
+     Rules used by the scheduler to determine where to place pods
+aka:
+tags:
+- fundamental
+---
+
+In Kubernetes, _affinity_ is a set of rules that give hints to the scheduler about where to place pods.
+
+<!--more-->
+There are two kinds of affinity:
+* [node affinity](/docs/concepts/scheduling-eviction/assign-pod-node/#node-affinity)
+* [pod-to-pod affinity](/docs/concepts/scheduling-eviction/assign-pod-node/#inter-pod-affinity-and-anti-affinity)
+
+The rules are defined using the Kubernetes {{< glossary_tooltip term_id="label" text="labels">}},
+and {{< glossary_tooltip term_id="selector" text="selectors">}} specified in {{< glossary_tooltip term_id="pod" text="pods" >}}, 
+and they can be either required or preferred, depending on how strictly you want the scheduler to enforce them.