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Upgrade go-connlimit to v0.3.0 / return http 429 on too many connections #8221

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Jul 3, 2020
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Upgrade go-connlimit to v0.3.0 / return http 429 on too many connections #8221

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2 changes: 1 addition & 1 deletion agent/agent.go
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Original file line number Diff line number Diff line change
Expand Up @@ -1154,7 +1154,7 @@ func (a *Agent) listenHTTP() ([]*HTTPServer, error) {
srv.Server.Handler = srv.handler(a.config.EnableDebug)

// Load the connlimit helper into the server
connLimitFn := a.httpConnLimiter.HTTPConnStateFunc()
connLimitFn := a.httpConnLimiter.HTTPConnStateFuncWithDefault429Handler(10 * time.Millisecond)
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I want to highlight this and explain what I think the implications are and make sure we are aware:

  • HTTPConnStateFunc closes the connection when it is beyond the limit. Close does not block.
  • HTTPConnStateFuncWithDefault429Handler(10 * time.Millisecond) blocks until the following is done (worst case):
    1. conn.SetDeadline(10*time.Millisecond) so that
    2. conn.Write(429error) is guaranteed to timeout after 10ms, so that the http 429 can be written and
    3. conn.Close can happen

The implication of this change is that accepting any new connection is worst case delayed by 10ms. But only after a client reached the limit already.

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Yes, indeed, you are fully correct. From my test, even by forcing very high latency with the clients, there ate no measurable change since write/close is fast because probably buffered by the OS.


if proto == "https" {
// Enforce TLS handshake timeout
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2 changes: 1 addition & 1 deletion go.mod
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Expand Up @@ -34,7 +34,7 @@ require (
github.com/hashicorp/go-bexpr v0.1.2
github.com/hashicorp/go-checkpoint v0.0.0-20171009173528-1545e56e46de
github.com/hashicorp/go-cleanhttp v0.5.1
github.com/hashicorp/go-connlimit v0.2.0
github.com/hashicorp/go-connlimit v0.3.0
github.com/hashicorp/go-discover v0.0.0-20200501174627-ad1e96bde088
github.com/hashicorp/go-hclog v0.12.0
github.com/hashicorp/go-memdb v1.1.0
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4 changes: 2 additions & 2 deletions go.sum
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Expand Up @@ -205,8 +205,8 @@ github.com/hashicorp/go-checkpoint v0.0.0-20171009173528-1545e56e46de/go.mod h1:
github.com/hashicorp/go-cleanhttp v0.5.0/go.mod h1:JpRdi6/HCYpAwUzNwuwqhbovhLtngrth3wmdIIUrZ80=
github.com/hashicorp/go-cleanhttp v0.5.1 h1:dH3aiDG9Jvb5r5+bYHsikaOUIpcM0xvgMXVoDkXMzJM=
github.com/hashicorp/go-cleanhttp v0.5.1/go.mod h1:JpRdi6/HCYpAwUzNwuwqhbovhLtngrth3wmdIIUrZ80=
github.com/hashicorp/go-connlimit v0.2.0 h1:OZjcfNxH/hPh/bT2Iw5yOJcLzz+zuIWpsp3I1S4Pjw4=
github.com/hashicorp/go-connlimit v0.2.0/go.mod h1:OUj9FGL1tPIhl/2RCfzYHrIiWj+VVPGNyVPnUX8AqS0=
github.com/hashicorp/go-connlimit v0.3.0 h1:oAojHGjFxUTTTA8c5XXnDqWJ2HLuWbDiBPTpWvNzvqM=
github.com/hashicorp/go-connlimit v0.3.0/go.mod h1:OUj9FGL1tPIhl/2RCfzYHrIiWj+VVPGNyVPnUX8AqS0=
github.com/hashicorp/go-discover v0.0.0-20200501174627-ad1e96bde088 h1:jBvElOilnIl6mm8S6gva/dfeTJCcMs9TGO6/2C6k52E=
github.com/hashicorp/go-discover v0.0.0-20200501174627-ad1e96bde088/go.mod h1:vZu6Opqf49xX5lsFAu7iFNewkcVF1sn/wyapZh5ytlg=
github.com/hashicorp/go-hclog v0.0.0-20180709165350-ff2cf002a8dd/go.mod h1:9bjs9uLqI8l75knNv3lV1kA55veR+WUPSiKIWcQHudI=
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6 changes: 3 additions & 3 deletions vendor/github.com/hashicorp/go-connlimit/README.md
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38 changes: 35 additions & 3 deletions vendor/github.com/hashicorp/go-connlimit/connlimit.go
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2 changes: 1 addition & 1 deletion vendor/modules.txt
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Expand Up @@ -197,7 +197,7 @@ github.com/hashicorp/go-bexpr
github.com/hashicorp/go-checkpoint
# github.com/hashicorp/go-cleanhttp v0.5.1
github.com/hashicorp/go-cleanhttp
# github.com/hashicorp/go-connlimit v0.2.0
# github.com/hashicorp/go-connlimit v0.3.0
github.com/hashicorp/go-connlimit
# github.com/hashicorp/go-discover v0.0.0-20200501174627-ad1e96bde088
github.com/hashicorp/go-discover
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