Add https and h2c to app-protocol for better HTTP/2 support, and deprecate app-ssl

[ItalyPaleAle]

In what area(s)?

/area runtime

Describe the proposal

Currently, Dapr can be configured to use 2 values for app-protcol:

• grpc
• http
  • Uses HTTPS if app-ssl is true

The app-ssl flag, which is probably misnamed (#6158), only applies to the HTTP app channel, and is ignored if the protocol is gRPC.

We can simplify this and instead add https as a protocol.

Why:

• This will make it easier for people to discover that we support HTTPS, which is something we should encourage since it enables using HTTP/2 (which can lead to much better perf)
• It's clearer since gRPC isn't impacted by app-ssl
• I have recently talked to a user who explained that now that we support HTTP/2, they were able to use HTTP for their app channel and at the same time use gRPC proxying to target the same app. This would be possible by setting app-channel to https. Fixes Can --app-protocol support both HTTP and grpc? #4291

We can also support h2c for the app channel, which is HTTP/2 Cleartext. This needs to be explicitly set for the protocol negotiation to work correctly.

We will maintain the app-ssl flag for backwards compatibility, but deprecated. When app-channel is set to http and app-ssl is enabled, we will switch the protocol to https

[yaron2]

+1

[ItalyPaleAle]

Looks like I was wrong on this:

The app-ssl flag [...] only applies to the HTTP app channel, and is ignored if the protocol is gRPC.

gRPC seems to be using that too.

Should we keep app-ssl (maybe renaming to app-tls) or introduce another protocol grpcs? I am also hoping to introduce h2c as protocol (HTTP/2 without TLS).

[daixiang0]

Agree.