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Comment by ialad

3 years ago

I'm using Go's default HTTP client to make a few requests per second. I set a context timeout of a few seconds for each request. There are random 16 minute intervals where I only get the error `context deadline exceeded`.

From what I found, Go's default client uses HTTP/2 by default. When a TCP connection stops working, it relies on the OS to decide when to time out the connection. Over HTTP/1.1, it closes the connection itself [1] on timeout and makes a new connection.

In Linux, I guess the timeout for a TCP connection depends on `tcp_retries2` which defaults to 15 and corresponds to a time of ~15m40s [2].

This can be simulated by making a client and some requests and then blocking traffic with an `iptables` rule [3]. My solution for now is to use a client that only uses HTTP/1.1.

[1] https://github.com/golang/go/issues/36026#issuecomment-56902...

[2] https://blog.cloudflare.com/when-tcp-sockets-refuse-to-die/

[3] https://github.com/golang/go/issues/30702

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ialad

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benmmurphy  3 years ago

that sounds like there is pooling going on and not invalidating the pooled connection when a timeout happens. I've actually seen a lot of libraries in other languages do a similar thing (my experience is some of the elixir libraries don't have good pool invalidation for http connections). having a default invalidation policy that handles all situations is a bit difficult but I think a default policy that invalidates on any timeout is much better than a default policy that never invalidates on a timeout. as long as invalidation means just evicting it from the pool and not tearing down other channels on the HTTP/2 connection. for example you could have a timeout on a HTTP/2 connection that is just on an individual channel but there is still data flowing through the other channels.

rattray  3 years ago

Wow. Can you easily change the tcp connection timeout?