[CWS] make sure we do not fetch the hostname multiple times (especially in tests)

[paulcacheux]

What does this PR do?

GetHostname can be pretty slow to call because it does some gRPC with the agent, and this can fail. To improve this, this PR adds a cache layer to ensure we do it only once when possible.

Motivation

Additional Notes

Possible Drawbacks / Trade-offs

Describe how to test/QA your changes

[pr-commenter]

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=37410029 --os-family=ubuntu

Note: This applies to commit 8e26148

[pr-commenter]

Regression Detector

Regression Detector Results

Run ID: e3a4906-4ce0-459c-8fcc-e69c966c1791 Metrics dashboard Target profiles

Baseline: 0637b28
Comparison: a92c521

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	links
➖	basic_py_check	% cpu utilization	+0.14	[-2.58, +2.86]	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	+0.00	[-0.01, +0.01]	Logs
➖	uds_dogstatsd_to_api	ingress throughput	-0.00	[-0.00, +0.00]	Logs
➖	idle	memory utilization	-0.07	[-0.11, -0.02]	Logs
➖	uds_dogstatsd_to_api_cpu	% cpu utilization	-0.22	[-1.10, +0.67]	Logs
➖	pycheck_1000_100byte_tags	% cpu utilization	-1.29	[-6.12, +3.54]	Logs
➖	otel_to_otel_logs	ingress throughput	-1.41	[-2.21, -0.60]	Logs
➖	tcp_syslog_to_blackhole	ingress throughput	-2.02	[-14.55, +10.52]	Logs
➖	file_tree	memory utilization	-2.79	[-2.93, -2.66]	Logs

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".

[paulcacheux]

/merge

[dd-devflow]

🚂 MergeQueue: pull request added to the queue

The median merge time in main is 29m.

Use /merge -c to cancel this operation!