Issue HTTP(S) requests

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Region ID

The REGION_ID is an abbreviated code that Google assigns based on the region you select when you create your app. The code does not correspond to a country or province, even though some region IDs may appear similar to commonly used country and province codes. For apps created after February 2020, REGION_ID.r is included in App Engine URLs. For existing apps created before this date, the region ID is optional in the URL.

Learn more about region IDs.

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This API is supported for first-generation runtimes and can be used when upgrading to corresponding second-generation runtimes. If you are updating to the App Engine runtime, refer to the Upgrade to second-generation runtimes page to learn about your migration options for legacy bundled services.

This page describes how to issue HTTP(S) requests from your App Engine app using the URL Fetch service for second-generation runtimes.

Before following the instructions on this page, we recommend you use language idiomatic solutions to issue HTTP(S) requests before using the URL Fetch service. The primary use case for using the URL Fetch is when you want to issue HTTP(S) requests to another App Engine app and assert your app's identity on that request.

For details on request size limits and which headers are sent in a URL Fetch request, see Outbound Requests.

Issuing an HTTP request

To use the URL Fetch service to issue outbound HTTP(S) requests, you must explicitly

Disabling redirects

Important: To improve the security of your app, it is recommended that you disable redirects.

If you are using URL Fetch, the underlying URL Fetch service follows up to five redirects by default. These redirects could forward sensitive information, such as authorization headers, to the redirected destination. If your app does not require HTTP redirects, it is recommended that you disable the redirects.

Issuing an HTTPS request

Issuing a request to another App Engine app

When using URL Fetch to issue a request to another App Engine app, your app can assert its identity by adding the header X-Appengine-Inbound-Appid to the request.

If you instruct the URL Fetch service to not follow redirects, App Engine will add this header to requests automatically. See Disabling redirects for guidance on disabling redirects.

Note: If you are making requests to another App Engine application, use its REGION_ID.r.appspot.com domain name rather than a custom domain for your app.

What's next

Learn about the URL Fetch service, such as the headers that are sent in a URL Fetch request in Outbound Requests.