Our Azure Service IP address is changed Suddenly.

[may zin]

Our Azure Service IP address is changed Suddenly. We don't want to get new IP address and want back the original IP because changing IP address will give us a lot of troubles. We have to change our serving clients' connection string one by one. is there any way we can get back the Original IP?

[#2]

Hello May,

Was IP Set to static or a reserved IP?

If the IP Address was not set to static or reserved there is no way to get it back. 

[#3]

If you are building web based applications hosted on Azure Web Apps (App Services) and require static outbound IP addresses then the following details will help you.
When provisioning Azure Web Apps (Azure App Services), a pool of IP addresses are allocated to the underlying scale unit of the web app and from what I have found the outbound IP addresses wont change if you stop/start the site or change to a different app service hosting plan (at least in my testing).
Also the App Service and App service plan have to be in the same region, you cannot move to a different app service plan located in a different region, the App service and plan both have to be in the same Azure region.
The outbound IP addresses will be released back into the global address pool when the web app is deleted. When redeployed a new range of IP addresses will be allocated for you from the available pool.
Also currently the only way to have a fixed IP for inbound traffic is via an internal IP with a web app hosted in an Application Service Environment (But that’s for another post). For now you access a web app via a load balanced endpoint such as <<mysite>>.azurewebsites.net.
Having fixed outbound IPs is very useful if you need to add a range of IPs to a whitelist for firewall rules and intra-service communication and the like. To find the outbound IP addresses for a given Web app, follow the steps below:
1) First select and click on the web app:

2) Scroll down and then select the properties section from the properties blade:

3) The outbound IP addresses will be shown as per the diagram:

Also I have spoken to some folks from Microsoft about this and here is a summary of what they told me:
1) Static outbound addresses associated with a scale unit do not change unless Microsoft makes a specific change to them.
2) Microsoft will also provide around 90 days notice if the IP addressed were to change on the backend.
3) Typically there is a fixed pool of about 4 or 5 outbound IP addresses per underlying scale unit.
4) The pool of addresses wont change without further advanced notification.

[#4 · Accepted solution]

@Sameer Salunke 

Thank for the information, very helpful.

We just encountered also that the outbound IP address changed. We would expect that the new outbound IP was one of the listed Outbound IP addresses specified on the Web App (listed in the Azure portal, Outbound IP Addresses).

However, we found out that our new Outbound IP address on the Web App was not listed anywhere. (we needed to made a function in our Web App which calls an external API, which return the IP address of our Web App).

As far as we know, we were not informed in advance of the IP change (and that the new IP was not listed in the outbound IP addresses).

For security reasons, I rather use the portal for this kind of security information exchange in stead of an email (with detailed IP numbers). 

Does this make senses to you and did anyone else encounter the same problem?