Update apply-rate-limiting-to-api.md
+### Applying ratelimiting to APIs
+
+Ratelimiting policies can be applied to the APIs created with the kubernetes operator, to throttle out requests according to the desired limit.
+
+Ratelimiting controller obtains the policies in the below 2 methods.
+* User defined policies
+* Set of default policies
+
+The ratelimiting controller uses the policies deployed to create a policy template configmap, which gets updated when user deploy ratelimiting policies.
+This policy cofigmap is mounted to kaniko job by the API controller and used to create the docker image.
+
+#### How to deploy a ratelimiting policy
+
+Create a ratelimiting policy using the RateLimiting kind. You can create 3 types of policies with the RateLimiting kind as shown below.
+Include the limit from which you want to throttle the API requests.
+
+* Application throttling
+```
+apiVersion: wso2.com/v1alpha1
+kind: RateLimiting
+metadata:
+ name: app4
+ namespace: wso2-test-ns
+spec:
+ type: application
+ description: Allow 4 requests per minute # optional
+ timeUnit: min
+ unitTime: 1
+ requestCount:
+ limit: 4
+```
+
+* Subscription throttling
+```
+apiVersion: wso2.com/v1alpha1
+kind: RateLimiting
+metadata:
+ name: sub6
+ namespace: wso2-test-ns
+spec:
+ type: subscription
+ description: Allow 6 requests per minute # optional
+ timeUnit: min
+ unitTime: 1
+ requestCount:
+ limit: 6
+```
+* Advance throttling
+```
+apiVersion: wso2.com/v1alpha1
+kind: RateLimiting
+metadata:
+ name: advance3
+ namespace: wso2-test-ns
+spec:
+ type: advance
+ description: Allow 3 requests per minute # optional
+ timeUnit: min
+ unitTime: 1
+ requestCount:
+ limit: 3
+```
+
+Implementation to the ratelimiting controller is found [here](https://github.com/wso2/k8s-apim-operator/blob/master/apim-operator/pkg/controller/ratelimiting/ratelimiting_controller.go)
