Hey everyone,
I read that response streaming through Function URLs isn't supported for Lambdas within a VPC, as per AWS documentation. However, I have a Lambda function connected to a VPC that's set up with private subnets and a NAT gateway. When I invoke it using a Function URL with `invoke-mode: RESPONSE_STREAM`, I see the response chunks streaming to my client without any buffering issues. I tested this using `curl -N`.
Has anyone else had a similar experience? Is this behavior officially supported, or could it just be a fluke because of my NAT configuration? I'm a bit worried it might stop working in the future.
Thanks for any insights!
3 Answers
I ran a DNS query from my client and the Function URL resolves to several AWS IPs in eu-west-1: 34.242.183.167, 34.243.63.215, and 18.203.108.102.
If the docs say it’s unsupported but it’s working for you, you might be in a tricky spot—what we call 'undefined behavior' in tech. AWS doesn’t guarantee that this will continue to work. Your NAT gateway could be hiding the restrictions, but AWS could shut this down anytime. If response streaming is crucial to your application, don’t rely on this working in the long run until AWS updates their documentation. A good idea would be to log a support ticket to create a paper trail for your situation.
Have you checked what the function URL hostname resolves to when queried from your test client? That might give more clues about how it's working.
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