Introduce SlowOpenToxic to approximate the TCP handshake latency #536
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Introduce a new toxic (`slow_open` / `SlowOpenToxic`) that adds a delay to the first data packet of a new TCP connection. This simulates the delay affecting the TCP handshake (SYN + SYN/ACK), which is not covered by the `latency` toxic.
Also: improve tests for latency toxic to check that every packet is subject to the added latency.
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As discussed in #123, the TCP handshake is performed by the kernel, so toxiproxy cannot inject latency there. Therefore, effects of latency on connection timeouts cannot be tested using this tool.
However, a user might be interested in the overall effects of latency from an application point of view. That is, the end-to-end effect on an entire conversation (TCP connection, application request, application response).
Using the
LatencyToxiconly, this end-to-end effect is not accurately modeled, because the initial RTT would be missing.This pull request introduces a new toxic,
SlowOpenToxic, that simulates the handshake latency by adding a delay to the first data packet only. I hope you'll find it useful!Latencies breakdown
In reality, you would have:
Using Toxiproxy, with a
SlowOpenToxicand aLatencyToxic(with the same delay, equal to 1 RTT), you would have:SlowOpenToxicand 1-RTT delay added byLatencyToxic)LatencyToxic).Implementation notes
LatencyToxic. Once the first packet has been processed, a persisted State records the event and makes the toxic warm. From that point, this toxic is transparent.LatencyToxictests (doLatencyRound) in order to:SlowOpenToxictests.LatencyToxicandSlowOpenToxic. To do this, I also tweaked the harness (at toxic_test.go:69) to process multiple packets, instead of stopping at the first one.