[EVPProxy] Do not manually cancel the request context

[albertvaka]

Context

In #26336 I added a timeout to the request context so that requests don't wait forever.

However, I also added a defer ctxCancel() call that manually cancelled the context at the end of the RoundTrip. This is not necessary because the parent context will already be cancelled when done, and furthermore it was causing problems with chunked (Transfer-Encoding: chunked) responses.

What does this PR do?

Do not cancel the context manually.

Describe how to test/QA your changes

There's a reproducer in this ticket: https://datadoghq.atlassian.net/browse/SDTEST-1010?focusedCommentId=1947043

[cit-pr-commenter]

Regression Detector

Regression Detector Results

Run ID: 1aa29056-0368-4b9f-8dc3-931c3777faa2 Metrics dashboard Target profiles

Baseline: 5f96339
Comparison: b0b8522

Performance changes are noted in the perf column of each table:

• ✅ = significantly better comparison variant performance
• ❌ = significantly worse comparison variant performance
• ➖ = no significant change in performance

No significant changes in experiment optimization goals

Confidence level: 90.00%
Effect size tolerance: |Δ mean %| ≥ 5.00%

There were no significant changes in experiment optimization goals at this confidence level and effect size tolerance.

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	pycheck_lots_of_tags	% cpu utilization	+1.01	[-1.50, +3.52]	1	Logs
➖	otel_to_otel_logs	ingress throughput	+0.68	[-0.14, +1.49]	1	Logs
➖	file_to_blackhole_1000ms_latency	egress throughput	+0.49	[-0.00, +0.97]	1	Logs
➖	idle	memory utilization	+0.26	[+0.22, +0.31]	1	Logs bounds checks dashboard
➖	file_tree	memory utilization	+0.16	[+0.03, +0.29]	1	Logs
➖	idle_all_features	memory utilization	+0.09	[-0.02, +0.20]	1	Logs bounds checks dashboard
➖	tcp_syslog_to_blackhole	ingress throughput	+0.09	[+0.04, +0.14]	1	Logs
➖	file_to_blackhole_500ms_latency	egress throughput	+0.07	[-0.18, +0.32]	1	Logs
➖	file_to_blackhole_0ms_latency	egress throughput	+0.03	[-0.31, +0.36]	1	Logs
➖	file_to_blackhole_100ms_latency	egress throughput	+0.03	[-0.20, +0.25]	1	Logs
➖	uds_dogstatsd_to_api	ingress throughput	+0.01	[-0.10, +0.12]	1	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.01, +0.01]	1	Logs
➖	file_to_blackhole_300ms_latency	egress throughput	-0.06	[-0.24, +0.12]	1	Logs
➖	uds_dogstatsd_to_api_cpu	% cpu utilization	-1.01	[-1.73, -0.29]	1	Logs
➖	basic_py_check	% cpu utilization	-1.06	[-3.86, +1.75]	1	Logs

Bounds Checks

perf	experiment	bounds_check_name	replicates_passed
✅	file_to_blackhole_0ms_latency	memory_usage	10/10
✅	file_to_blackhole_1000ms_latency	memory_usage	10/10
✅	file_to_blackhole_100ms_latency	memory_usage	10/10
✅	file_to_blackhole_300ms_latency	memory_usage	10/10
✅	file_to_blackhole_500ms_latency	memory_usage	10/10
✅	idle	memory_usage	10/10
✅	idle_all_features	memory_usage	10/10

Explanation

A regression test is an A/B test of target performance in a repeatable rig, where "performance" is measured as "comparison variant minus baseline variant" for an optimization goal (e.g., ingress throughput). Due to intrinsic variability in measuring that goal, we can only estimate its mean value for each experiment; we report uncertainty in that value as a 90.00% confidence interval denoted "Δ mean % CI".

For each experiment, we decide whether a change in performance is a "regression" -- a change worth investigating further -- if all of the following criteria are true:

1. Its estimated |Δ mean %| ≥ 5.00%, indicating the change is big enough to merit a closer look.

2. Its 90.00% confidence interval "Δ mean % CI" does not contain zero, indicating that if our statistical model is accurate, there is at least a 90.00% chance there is a difference in performance between baseline and comparison variants.

3. Its configuration does not mark it "erratic".

[agent-platform-auto-pr]

Test changes on VM

Use this command from test-infra-definitions to manually test this PR changes on a VM:

inv create-vm --pipeline-id=46861673 --os-family=ubuntu

Note: This applies to commit 58e99d6

[ajgajg1134]

👋 Overall this change looks fine, can you add (or modify an existing) test to confirm this change and ensure it doesn't regress in the future? Once that's done you can add a qa/done label as well! Thanks!

[albertvaka]

I though writing an automated test for this case would be super hard, but it was actually nice and simple 😮 I added a test that fails with the previous code and passes now 👌

[ajgajg1134]

Thanks for adding that test! :)

[albertvaka]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in main is 25m.

Use /merge -c to cancel this operation!