[NTP] generate ntp.offset metric based from intake's HTTP response

[ian28223]

What does this PR do?

Introduces another ntp.offset metric with source:intake tag. This metric is derived from the Date HTTP response header from intake communications and provides an alternative to NTP-based clock monitoring.
Original ntp.offset metric calculated from an actual NTP server will now be tagged source:ntp

Key changes:

• Capture the Date header from successful HTTP responses in the forwarder
• Store the calculated intake offset in an expvar for global access
• Submit ntp.offset metric with source:intake tag from the NTP check (independent of NTP query success)
• Display both "NTP offset" and "Intake offset" in the agent status Clocks section, if available. e.g.

  Clocks
  ======
  
  NTP offset: -7m2.716699s
  Intake offset: -7m3.061178s
  

• Update NTP check tests to accommodate the new metric submission

Motivation

It's common for NTP checks to fail due to firewall restrictions while remaining enabled in agent configurations. When the system clock drifts significantly, the Datadog intake begins dropping metrics, leading to missing data despite the agent running normally. This often goes unnoticed until data gaps are discovered.

This PR addresses the issue by:

1. Providing clock drift visibility even when NTP is blocked by firewalls provided the Agent has access to DD intake.
2. Using existing intake communication to monitor time offset without additional network requirements

Describe how you validated your changes

• ✅ Verified all modified packages compile successfully
• ✅ Updated unit tests to expect the new source:intake tagged metric
• ✅ Validated that intake offset is submitted independently of NTP check success/failure
• ✅ Verified status templates display both offsets correctly
• ✅ Tested with system time set ahead/behind to confirm sign convention matches current NTP metric
• ✅ Confirmed intake offset continues working when UDP port 123 (NTP) is blocked

Additional Notes

• The ntp.offset metric now has two variants distinguished by the source tag: source:ntp and source:intake
• Both sources use NTP sign convention: positive offset means agent clock is behind (needs to add time), negative means agent is ahead (needs to subtract time)
• The intake offset is calculated as: serverTime.Sub(agentTime).Seconds() from the HTTP Date header
• The metric timestamp uses the intake server's time perspective (agent_time + offset), ensuring the metric appears at the correct time from Datadog's perspective even when there is clock drift
• When the intakeOffset expvar is not set (NaN), the metric is not submitted
• This implementation maintains backward compatibility - existing ntp.offset queries without tag filters will include both sources
• The expvar intakeOffset is only created once in transaction.go; ntp.go reads it using expvar.Get()

[agent-platform-auto-pr]

Static quality checks

✅ Please find below the results from static quality gates
Comparison made with ancestor c8b028a
📊 Static Quality Gates Dashboard

Successful checks

Info

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64_fips	+2.37 KiB (0.00% increase)	696.958 → 696.961 → 704.000
✅	agent_heroku_amd64	+4.09 KiB (0.00% increase)	325.730 → 325.734 → 329.530
✅	agent_msi	+3.5 KiB (0.00% increase)	659.808 → 659.812 → 1072.620
✅	agent_rpm_amd64_fips	+2.37 KiB (0.00% increase)	696.942 → 696.944 → 703.990
✅	agent_rpm_arm64_fips	+4.27 KiB (0.00% increase)	679.415 → 679.419 → 688.480
✅	agent_suse_amd64_fips	+2.37 KiB (0.00% increase)	696.942 → 696.944 → 703.990
✅	agent_suse_arm64_fips	+4.27 KiB (0.00% increase)	679.415 → 679.419 → 688.480
✅	iot_agent_deb_arm64	+4.09 KiB (0.01% increase)	39.860 → 39.864 → 40.920
✅	iot_agent_deb_armhf	+4.03 KiB (0.01% increase)	40.431 → 40.434 → 41.030

22 successful checks with minimal change (< 2 KiB)

	Quality gate	Current Size
✅	agent_deb_amd64	748.166 MiB
✅	agent_rpm_amd64	748.150 MiB
✅	agent_rpm_arm64	727.267 MiB
✅	agent_suse_amd64	748.150 MiB
✅	agent_suse_arm64	727.267 MiB
✅	docker_agent_amd64	810.646 MiB
✅	docker_agent_arm64	814.354 MiB
✅	docker_agent_jmx_amd64	1001.525 MiB
✅	docker_agent_jmx_arm64	993.952 MiB
✅	docker_cluster_agent_amd64	180.844 MiB
✅	docker_cluster_agent_arm64	196.670 MiB
✅	docker_cws_instrumentation_amd64	7.135 MiB
✅	docker_cws_instrumentation_arm64	6.689 MiB
✅	docker_dogstatsd_amd64	38.414 MiB
✅	docker_dogstatsd_arm64	36.749 MiB
✅	dogstatsd_deb_amd64	29.630 MiB
✅	dogstatsd_deb_arm64	27.802 MiB
✅	dogstatsd_rpm_amd64	29.630 MiB
✅	dogstatsd_suse_amd64	29.630 MiB
✅	iot_agent_deb_amd64	42.743 MiB
✅	iot_agent_rpm_amd64	42.743 MiB
✅	iot_agent_suse_amd64	42.743 MiB

On-wire sizes (compressed)

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64	-10.43 KiB (0.01% reduction)	182.879 → 182.869 → 184.810
✅	agent_deb_amd64_fips	+53.61 KiB (0.03% increase)	171.299 → 171.351 → 173.790
✅	agent_heroku_amd64	+5.52 KiB (0.01% increase)	87.252 → 87.257 → 88.450
✅	agent_msi	-12.0 KiB (0.01% reduction)	142.414 → 142.402 → 143.300
✅	agent_rpm_amd64	-34.88 KiB (0.02% reduction)	185.857 → 185.823 → 188.160
✅	agent_rpm_amd64_fips	-3.28 KiB (0.00% reduction)	173.619 → 173.616 → 176.600
✅	agent_rpm_arm64	-9.77 KiB (0.01% reduction)	168.370 → 168.361 → 169.930
✅	agent_rpm_arm64_fips	+45.22 KiB (0.03% increase)	158.964 → 159.008 → 160.550
✅	agent_suse_amd64	-34.88 KiB (0.02% reduction)	185.857 → 185.823 → 188.160
✅	agent_suse_amd64_fips	-3.28 KiB (0.00% reduction)	173.619 → 173.616 → 176.600
✅	agent_suse_arm64	-9.77 KiB (0.01% reduction)	168.370 → 168.361 → 169.930
✅	agent_suse_arm64_fips	+45.22 KiB (0.03% increase)	158.964 → 159.008 → 160.550
✅	docker_agent_amd64	neutral	275.112 MiB → 277.400
✅	docker_agent_arm64	neutral	262.702 MiB → 266.040
✅	docker_agent_jmx_amd64	+3.11 KiB (0.00% increase)	343.748 → 343.751 → 346.020
✅	docker_agent_jmx_arm64	+13.74 KiB (0.00% increase)	327.322 → 327.336 → 330.660
✅	docker_cluster_agent_amd64	neutral	63.868 MiB → 64.510
✅	docker_cluster_agent_arm64	+5.53 KiB (0.01% increase)	60.151 → 60.157 → 61.170
✅	docker_cws_instrumentation_amd64	neutral	2.994 MiB → 3.330
✅	docker_cws_instrumentation_arm64	neutral	2.726 MiB → 3.090
✅	docker_dogstatsd_amd64	neutral	14.864 MiB → 15.820
✅	docker_dogstatsd_arm64	+9.82 KiB (0.07% increase)	14.198 → 14.208 → 14.830
✅	dogstatsd_deb_amd64	neutral	7.831 MiB → 8.790
✅	dogstatsd_deb_arm64	+4.03 KiB (0.06% increase)	6.716 → 6.720 → 7.710
✅	dogstatsd_rpm_amd64	neutral	7.843 MiB → 8.800
✅	dogstatsd_suse_amd64	neutral	7.843 MiB → 8.800
✅	iot_agent_deb_amd64	+2.04 KiB (0.02% increase)	11.210 → 11.212 → 12.040
✅	iot_agent_deb_arm64	neutral	9.585 MiB → 10.450
✅	iot_agent_deb_armhf	+2.94 KiB (0.03% increase)	9.777 → 9.780 → 10.620
✅	iot_agent_rpm_amd64	+3.66 KiB (0.03% increase)	11.227 → 11.231 → 12.060
✅	iot_agent_suse_amd64	+3.66 KiB (0.03% increase)	11.227 → 11.231 → 12.060

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: 8fd9c654-cfe2-4893-affc-2f37d1c4b6c3

Baseline: c8b028a
Comparison: 74250c8
Diff

Optimization Goals: ✅ No significant changes detected

Experiments ignored for regressions

Regressions in experiments with settings containing erratic: true are ignored.

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	docker_containers_cpu	% cpu utilization	-1.78	[-4.86, +1.30]	1	Logs

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	tcp_syslog_to_blackhole	ingress throughput	+1.97	[+1.88, +2.07]	1	Logs
➖	ddot_logs	memory utilization	+0.63	[+0.55, +0.70]	1	Logs
➖	docker_containers_memory	memory utilization	+0.63	[+0.55, +0.70]	1	Logs
➖	ddot_metrics_sum_delta	memory utilization	+0.31	[+0.12, +0.50]	1	Logs
➖	quality_gate_metrics_logs	memory utilization	+0.20	[-0.03, +0.43]	1	Logs bounds checks dashboard
➖	otlp_ingest_logs	memory utilization	+0.16	[+0.05, +0.26]	1	Logs
➖	uds_dogstatsd_20mb_12k_contexts_20_senders	memory utilization	+0.12	[+0.07, +0.17]	1	Logs
➖	uds_dogstatsd_to_api_v3	ingress throughput	+0.01	[-0.13, +0.15]	1	Logs
➖	uds_dogstatsd_to_api	ingress throughput	+0.01	[-0.12, +0.14]	1	Logs
➖	file_to_blackhole_100ms_latency	egress throughput	+0.01	[-0.04, +0.05]	1	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.10, +0.09]	1	Logs
➖	file_to_blackhole_1000ms_latency	egress throughput	-0.01	[-0.43, +0.41]	1	Logs
➖	file_tree	memory utilization	-0.01	[-0.06, +0.03]	1	Logs
➖	ddot_metrics_sum_cumulativetodelta_exporter	memory utilization	-0.04	[-0.27, +0.19]	1	Logs
➖	file_to_blackhole_0ms_latency	egress throughput	-0.08	[-0.61, +0.44]	1	Logs
➖	file_to_blackhole_500ms_latency	egress throughput	-0.10	[-0.49, +0.28]	1	Logs
➖	ddot_metrics	memory utilization	-0.16	[-0.37, +0.05]	1	Logs
➖	ddot_metrics_sum_cumulative	memory utilization	-0.19	[-0.35, -0.03]	1	Logs
➖	quality_gate_idle	memory utilization	-0.20	[-0.24, -0.16]	1	Logs bounds checks dashboard
➖	quality_gate_idle_all_features	memory utilization	-0.42	[-0.46, -0.38]	1	Logs bounds checks dashboard
➖	otlp_ingest_metrics	memory utilization	-0.59	[-0.75, -0.43]	1	Logs
➖	quality_gate_logs	% cpu utilization	-0.63	[-2.12, +0.86]	1	Logs bounds checks dashboard
➖	docker_containers_cpu	% cpu utilization	-1.78	[-4.86, +1.30]	1	Logs

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	links
✅	docker_containers_cpu	simple_check_run	10/10
✅	docker_containers_memory	memory_usage	10/10
✅	docker_containers_memory	simple_check_run	10/10
✅	file_to_blackhole_0ms_latency	lost_bytes	10/10
✅	file_to_blackhole_0ms_latency	memory_usage	10/10
✅	file_to_blackhole_1000ms_latency	lost_bytes	10/10
✅	file_to_blackhole_1000ms_latency	memory_usage	10/10
✅	file_to_blackhole_100ms_latency	lost_bytes	10/10
✅	file_to_blackhole_100ms_latency	memory_usage	10/10
✅	file_to_blackhole_500ms_latency	lost_bytes	10/10
✅	file_to_blackhole_500ms_latency	memory_usage	10/10
✅	quality_gate_idle	intake_connections	10/10	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	bounds checks dashboard
✅	quality_gate_logs	lost_bytes	10/10	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	bounds checks dashboard
✅	quality_gate_metrics_logs	intake_connections	10/10	bounds checks dashboard
✅	quality_gate_metrics_logs	lost_bytes	10/10	bounds checks dashboard
✅	quality_gate_metrics_logs	memory_usage	10/10	bounds checks dashboard

Explanation

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

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

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".

CI Pass/Fail Decision

✅ Passed. All Quality Gates passed.

• quality_gate_metrics_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check lost_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check lost_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.

[fabbing]

I think @vickenty suggestions should be applied, besides that LGTM!