On Wed, Feb 22, 2017 at 8:42 PM, Eric Wong <e...@80x24.org> wrote: > Simon Eskildsen <simon.eskild...@shopify.com> wrote: > > <snip> Thanks for the writeup! > > Another sidenote: It seems nginx <-> unicorn is a bit odd > for deployment in a containerized environment(*). > >> I meant to ask, in Raindrops why do you use the netlink API to get the >> socket backlog instead of `getsockopt(2)` with `TCP_INFO` to get >> `tcpi_unacked`? (as described in >> http://www.ryanfrantz.com/posts/apache-tcp-backlog/) We use this to >> monitor socket backlogs with a sidekick Ruby daemon. Although we're >> looking to replace it with a middleware to simplify for Kubernetes. >> It's one of our main metrics for monitoring performance, especially >> around deploys. > > The netlink API allows independently-spawned processes to > monitor others; so it can be system-wide. TCP_INFO requires the > process doing the checking to also have the socket open. > > I guess this reasoning for using netlink is invalid for containers, > though...
If you namespace the network it's problematic, yeah. I'm considering right now putting Raindrops in a middleware with the netlink API inside the container, but it feels weird. That said, if you consider the alternative of using `getsockopt(2)` on the listening socket, I don't know how you'd get access to the Unicorn listening socket from a middleware. Would it be nuts to expose a hook in Unicorn that allows periodic execution for monitoring listening stats from Raindrops on the listening socket? It seems somewhat of a narrow use-case, but on the other hand I'm also not a fan of doing `Raindrops::Linux.tcp_listener_stats("localhost:#{ENV["PORT"}")`, but that might be less ugly. > >> I was going to use `env["unicorn.socket"]`/`env["puma.socket"]`, but >> you could also do `env.delete("hijack_io")` after hijacking to allow >> Unicorn to still render the response. Unfortunately the >> `<webserver>.socket` key is not part of the Rack standard, so I'm >> hesitant to use it. When this gets into Unicorn I'm planning to >> propose it upstream to Puma as well. > > I was going to say env.delete("rack.hijack_io") is dangerous > (since env could be copied by middleware); but apparently not: > rack.hijack won't work with a copied env, either. > You only need to delete with the same env object you call > rack.hijack with. > > But calling rack.hijack followed by env.delete may still > have unintended side-effects in other servers; so I guess > we (again) cannot rely on hijack working portably. Exactly, it gives the illusion of portability but e.g. Puma stores an instance variable to check whether a middleware hijacked, rendering the `env#delete` option useless. > >> Cool. How would you suggest I check for TCP_INFO compatible platforms >> in Unicorn? Is `RUBY_PLATFORM.ends_with?("linux".freeze)` sufficient >> or do you prefer another mechanism? I agree that we should fall back >> to the write hack on other platforms. > > The Raindrops::TCP_Info class should be undefined on unsupported > platforms, so I think you can check for that, instead. Then it > should be transparent to add FreeBSD support from unicorn's > perspective. Perfect. I'll start working on a patch. > > > (*) So I've been wondering if adding a "unicorn-mode" to an > existing C10K, slow-client-capable Ruby/Rack server + > reverse proxy makes sense for containerized deploys. > Maybe... I'd love to hear more about this idea. What are you contemplating?