Happy eyeballs (fast fallback) in an Async environment?

[travisbell]

Hey Samuel,

I came across a bit of unique scenario with regards to a dual stack DNS address that I am trying to figure out. To be fair, this doesn't affect our production environment but is something I noticed in my local development environment since we connect to a VPN with only IPv4 addresses.

irb(main):009> Resolv.getaddresses("some-random-aws-service.aos.us-east-1.on.aws")
=> ["2600:1f28:372:c403:ccda:45e8:2797:6b54", "172.24.186.66"]

irb(main):010> Addrinfo.ip("some-random-aws-service.aos.us-east-1.on.aws")
=> #<Addrinfo: 2600:1f28:372:c403:ccda:45e8:2797:6b54 (some-random-aws-service.aos.us-east-1.on.aws)>

When I try and use this address with Async::HTTP, I just get a timeout because it's trying to connect to the (I think first(?) address which is IPv6:

irb(main):005> Async::HTTP::Internet.get("https://some-random-aws-service.aos.us-east-1.on.aws")
/Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/io-endpoint-0.15.2/lib/io/endpoint/wrapper.rb:58:in 'Socket#connect': Operation timed out - connect(2) for [2600:1f28:372:c403:ccda:45e8:2797:6b54]:443 (Errno::ETIMEDOUT)
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/io-endpoint-0.15.2/lib/io/endpoint/wrapper.rb:58:in 'IO::Endpoint::Wrapper#socket_connect'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/io-endpoint-0.15.2/lib/io/endpoint/wrapper.rb:99:in 'IO::Endpoint::Wrapper#connect'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/io-endpoint-0.15.2/lib/io/endpoint/host_endpoint.rb:46:in 'block in IO::Endpoint::HostEndpoint#connect'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/3.4.0/socket.rb:231:in 'Array#each'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/3.4.0/socket.rb:231:in 'Addrinfo.foreach'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/io-endpoint-0.15.2/lib/io/endpoint/host_endpoint.rb:44:in 'IO::Endpoint::HostEndpoint#connect'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/io-endpoint-0.15.2/lib/io/endpoint/ssl_endpoint.rb:159:in 'IO::Endpoint::SSLEndpoint#connect'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-http-0.89.0/lib/async/http/endpoint.rb:220:in 'Async::HTTP::Endpoint#connect'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-http-0.89.0/lib/async/http/client.rb:169:in 'block in Async::HTTP::Client#make_pool'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-pool-0.11.0/lib/async/pool/controller.rb:324:in 'Async::Pool::Controller#create_resource'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-pool-0.11.0/lib/async/pool/controller.rb:394:in 'Async::Pool::Controller#acquire_or_create_resource'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-pool-0.11.0/lib/async/pool/controller.rb:343:in 'block in Async::Pool::Controller#available_resource'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-2.27.0/lib/async/semaphore.rb:87:in 'Async::Semaphore#acquire'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-pool-0.11.0/lib/async/pool/controller.rb:342:in 'Async::Pool::Controller#available_resource'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-pool-0.11.0/lib/async/pool/controller.rb:312:in 'Async::Pool::Controller#wait_for_resource'
	from /Users/travisbell/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/async-pool-0.11.0/lib/async/pool/controller.rb:155:in 'Async::Pool::Controller#acquire'

Yet, when I use Net::HTTP, everything succeeds:

irb(main):006> Net::HTTP.get(URI("https://some-random-aws-service.aos.us-east-1.on.aws"))
=> "successful response body..."

I know a lot of work was done in Ruby 3.4 to support happy eyeballs v2 (RFC8305)... is this something we need to also build out in the Async libraries?

Thanks as always!

[ioquatix]

This is on my to-do list, and will be implemented in the io-endpoint gem as we have all the specific pieces available to us.

[travisbell]

Ah, groovy! Good to know it's on your radar.