Merge pull request kubernetes-sigs#942 from vladimirmukhin/waf_documentation

Add documentation about configuring WAF

Author: k8s-ci-robot

docs/guide/ingress/annotation.md

@@ -43,6 +43,7 @@ You can add kubernetes annotations to ingress and service objects to customize t
 |[alb.ingress.kubernetes.io/target-group-attributes](#target-group-attributes)|stringMap|N/A|ingress,service|
 |[alb.ingress.kubernetes.io/target-type](#target-type)|instance \| ip|instance|ingress,service|
 |[alb.ingress.kubernetes.io/unhealthy-threshold-count](#unhealthy-threshold-count)|integer|'2'|ingress,service|
+|[alb.ingress.kubernetes.io/waf-acl-id](#waf-acl-id)|string|N/A|ingress|
 
 ## Traffic Listening
 Traffic Listening can be controlled with following annotations:
@@ -328,6 +329,16 @@ Health check on target groups can be controlled with following annotations:
  ```alb.ingress.kubernetes.io/unhealthy-threshold-count: '2'
  ```
 
+## WAF
+- <a name="waf-acl-id">`alb.ingress.kubernetes.io/waf-acl-id`</a> specifies the identifier for the Amzon WAF web ACL.
+
+ !!!warning ""
+ Only Regional WAF is supported.
+
+ !!!example
+ ```alb.ingress.kubernetes.io/waf-acl-id: 499e8b99-6671-4614-a86d-adb1810b7fbe
+ ```
+
 ## SSL
 SSL support can be controlled with following annotations: