h2_backend - no Host header

Questions / Help
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1

Given that self-managed HTTP/2 via handlers = [“tls”] is no longer supported, I decided to switch. Previously, I had the following setup

[[services]]
  internal_port = 5202
  protocol = "tcp"
  auto_stop_machines = true
  auto_start_machines = true
  min_machines_running = 1
  [[services.ports]]
    handlers = ["tls"]
    port = "9090"
    tls_options = { alpn = ["h2"] }

I have switched this to the new setup:

[[services]]
  internal_port = 5202
  protocol = "tcp"
  auto_stop_machines = true
  auto_start_machines = true
  min_machines_running = 1
  [[services.ports]]
    handlers = ["tls", "http"]
    port = 9090
    tls_options = { alpn = ["h2"] }
    http_options = { h2_backend = true }

This works. But there is a differnce in the Host header. Previously, I received my.app as the Host, now it is something like 172.19.137.34.

I need to know the original Host. An additional http_service hosted on the same machine receives the correct Host header without problems. I also echoed back the HTTP headers to debug this issue and there is no additional information that could help me discern the original Host.

This was already reported in h2_backend loses incoming request host information , but I can still reproduce it.

2

Hey @CommonGuy

Yeah, with h2_backend we currently don’t properly forward :authority: pseudo-header. This is on our TODO list, but no ETA at the moment.

We still set Host header even for http/2, though, so it should be available to your app.

Could use share a reproducer that shows the problem, please?

I’ve just tested it with a simple Go app and I see the original host header just fine.

3

Thank you for the quick answer. Based on my research, it seems that .NET (or rather Kestrel, the webserver) replaces the Host header with the :authority: value completely to prevent mismatched values. That’s why I cannot see the actual Host header. See aspnetcore/src/Servers/Kestrel/Core/src/Internal/Http2/Http2Stream.cs at main · dotnet/aspnetcore · GitHub

So properly setting the :authority: header would be much appreciated

5

@CommonGuy

Could you share your app’s name, please? If you don’t want to share it publicly, feel free to drop me an email to pavel fly.io.

I’ve just rolled out a fix for this. It’s behind a feature flag which I’m gonna gradually enable for all apps in the coming days. I can switch it on for your app first, if you want.

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6

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