Refer to "Google App Engine Java new performant HTTP connector" document. https://github.com/GoogleCloudPlatform/appengine-java-standard/blob/main/httpconnector.md

So I decide to test with my app. After I add this below properties into appengine-web.xml

property name="appengine.use.httpconnector" value="true"

and then re-deploy the service. Perform testing by HTTP GET on the browser, it's return status 403. And display the message: Error: !Secure" on the browser.

So I have revert it by change the value from 'true' to 'false' and re-deploy everything work as usual.

My environement is below ...
Runtime: java17
Using app-engine-apis: true
on F4 instance, automatic scaling.

Anybody has this kind of issue like me?