Google uses a wide range of IP addresses for its different services, and the addresses may change without notification. Google App Engine is a Platform as a Service offering which hosts a wide variety of 3rd party applications. This post announces changes in the IP address range and headers used by the Google App Engine URLFetch (outbound HTTP) and outbound sockets APIs.

While we recommend that App Engine IP ranges not be used to filter inbound requests, we are aware that some services have created filters that rely on specific addresses. Google App Engine will be changing its IP range beginning this month. Please see these instructions to determine App Engine’s IP range.

Additionally, the HTTP User-Agent header string that historically allowed identification of individual App Engine applications should no longer be relied on to identify the application. With the introduction of outbound sockets for App Engine, applications may now make HTTP requests without using the URLFetch API, and those requests may set a User-Agent of their own choosing.