Can anyone else use the app service outbound IP address?

Question

If I use only one web app and I have a lot of outbound IP addresses, can Azure give them to another app service that I do not own, or do these IPs belong to me even if I do not use them?

Answer 1

"All App Service plans in the same deployment unit, and app instances that run in them, share the same set of virtual IP addresses. For an App Service Environment (an App Service plan in Isolated tier), the App Service plan is the deployment unit itself, so the virtual IP addresses are dedicated to it as a result."

Reference: How IP addresses work in App Service

If I got it well, it's not your own ip addresses if you don't have isolated tier.

The set of outbound IP addresses for your app changes when you perform one of the following actions:

• Delete an app and recreate it in a different resource group (deployment unit may change).
• Delete the last app in a resource group and region combination and recreate it (deployment unit may change).
• Scale your app between the lower tiers (Basic, Standard, and Premium), the PremiumV2 tier, the PremiumV3 tier, and the Pmv3 options within the PremiumV3 tier (IP addresses may be added to or subtracted from the set).

Reference: When outbound IPs change

In answer to your question, if you do not perform the actions listed above, in theory you will still have the IPs you are not using. BTW, you can't actually decide which IP you're using based on the description, because the app service plan decides on the fly, but they belong to you.

Any outbound connection from the App Service app, such as to a back-end database, uses one of the outbound IP addresses as the origin IP address. The IP address to use is selected randomly at runtime, so your back-end service must open its firewall to all the outbound IP addresses for your app.

Reference: When outbound IPs change