Zero Downtime Failover Description (cloudflare#4947)

Author: patriciasantaana

content/load-balancing/understand-basics/session-affinity.md

@@ -55,6 +55,16 @@ Origin drain is not supported for load balancers in [DNS-only mode (gray cloud)]
 
 {{</Aside>}}
 
+### Zero Downtime Failover
+
+Zero Downtime Failover automatically sends traffic to origin servers within a pool during transient network issues. This helps reduce errors shown to your users when issues occur in between active health monitors. 
+
+You can enable one of three options:
+
+- **None**: No failover will take place and errors may show to your users.
+- **Temporary**: Traffic will be sent to other origin(s) until the originally pinned origin is available.
+- **Sticky**: The session affinity cookie is updated and subsequent requests are sent to the new origin moving forward as needed.
+
 ---
 
 ## Enabling Session Affinity via the Cloudflare API