If you want to perform IP whitelisting against an App Service, you'll discover that on public instances of App Service (not App Service Environment) you have 4 or more outbound IP addresses.
I was in a situation where I needed to get all outbound IP addresses over multiple subscriptions for IP whitelisting purposes. With the help of PowerShell I created a little script that will do just that here is an example of the output:
.\Get-AppServiceWebAppsOutboundIpAddresses.ps1' -SubscriptionName 'mysub1','mysub2
Switching to subscription mysub1
Switching to subscription mysub2
Count IpAddress Sites
----- ---- -----
2 13.85.17.60 {sub1-bi-dev-as-webapp, sub2-bi-prod-as-webapp}
2 13.85.20.144 {sub1-bi-prod-as-webapp, sub1-bi-dev-as-webapp}
2 13.85.22.206 {sub2-bi-prod-as-webapp, sub1-bi-dev-as-webapp}
2 13.85.23.148 {sub1-bi-dev-as-webapp, sub2-bi-prod-as-webapp}
2 13.85.23.243 {sub1-bi-dev-as-webapp, sub2-bi-prod-as-webapp}
1 23.96.184.12 {sub1-dev-functions-mmckydd}
1 23.96.184.209 {sub1-dev-functions-mmckydd}
1 23.96.186.252 {sub1-dev-functions-mmckydd}
1 23.96.187.50 {sub1-dev-functions-mmckydd}
5 23.96.244.71 {sub1-stg-webapp-web-n7wfdda, sub1-stg-functions-n7wfdda, sub1-stg-webapp-admin-n7wfdda, sub1-dev-ops-functions-stl4tn5...}
If you are interested to have a sorted, unique list of IPs used in your App Services, this script is for you.
You can get it on the Script Center:
https://gallery.technet.microsoft.com/scriptcenter/List-all-App-Service-web-4d563f14