feat(serverless-init): sequential flush on /terminate, bounded mirrorResponse write

[litianningdatadog]

Summary

• /terminate now flushes telemetry after forwarding to the user app (flushSequential), eliminating the race where logs produced by the user app during PassThrough could arrive in the pipeline after logsFlusher.Flush() had already returned. Since the VM is torn down on terminate, in-memory buffers are unrecoverable — sequential flush ensures the tail is captured.
• /suspend retains the parallel flush: Firecracker snapshots preserve process memory, so residual items survive and are drained on the next resume.
• Introduces flushMode type (noFlush / flushParallel / flushSequential) replacing the withFlush bool parameter; renames handleParallel → handleWithForwarder now that the function handles all three modes.
• mirrorResponse now sets an explicit write deadline via http.ResponseController (5 s), replacing the undocumented +10s WriteTimeout buffer. WriteTimeout is updated to forwardTimeout + flushTimeout + mirrorResponseTimeout to cover the /terminate sequential wall-clock.

Test plan

• dda inv test --targets=./cmd/serverless-init/lifecycle/ — all 133 tests pass
• Verify /terminate flushes after user-app response in integration test
• Verify /suspend still flushes in parallel (no latency regression)

🤖 Generated with Claude Code

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🔁 Mirror of internal PR: https://github.com/DataDog/datadog-agent-internal/pull/36

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[datadog-datadog-prod-us1-2]

🎯 Code Coverage (details)
• Patch Coverage: 92.59%
• Overall Coverage: 50.93% (+0.00%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 4661a98 | Docs | Datadog PR Page | Give us feedback!}

[dd-octo-sts]

Files inventory check summary

File checks results against ancestor de36884b:

Results for datadog-agent_7.82.0~devel.git.359.4661a98.pipeline.120862568-1_amd64.deb:

No change detected

[dd-octo-sts]

Static quality checks

✅ Please find below the results from static quality gates
Comparison made with ancestor de36884
📊 Static Quality Gates Dashboard
🔗 SQG Job

Successful checks

Info

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64	+2.0 KiB (0.00% increase, -0.02% of buffer)	747.693 → 747.695 → 758.200
✅	agent_deb_amd64_fips	+6.0 KiB (0.00% increase, -0.09% of buffer)	703.639 → 703.645 → 709.840
✅	agent_rpm_amd64	+2.0 KiB (0.00% increase, -0.02% of buffer)	747.677 → 747.679 → 758.170
✅	agent_rpm_amd64_fips	+6.0 KiB (0.00% increase, -0.09% of buffer)	703.623 → 703.629 → 709.840
✅	agent_suse_amd64	+2.0 KiB (0.00% increase, -0.02% of buffer)	747.677 → 747.679 → 758.170
✅	agent_suse_amd64_fips	+6.0 KiB (0.00% increase, -0.09% of buffer)	703.623 → 703.629 → 709.840
✅	docker_agent_amd64	+2.01 KiB (0.00% increase, -0.03% of buffer)	806.512 → 806.514 → 813.790
✅	docker_agent_jmx_amd64	+2.0 KiB (0.00% increase, -0.03% of buffer)	997.409 → 997.411 → 1004.550

24 successful checks with minimal change (< 2 KiB)

	Quality gate	Current Size
✅	agent_heroku_amd64	308.657 MiB
✅	agent_rpm_arm64	723.234 MiB
✅	agent_rpm_arm64_fips	682.787 MiB
✅	agent_suse_arm64	723.234 MiB
✅	agent_suse_arm64_fips	682.787 MiB
✅	docker_agent_arm64	807.085 MiB
✅	docker_agent_jmx_arm64	986.635 MiB
✅	docker_cluster_agent_amd64	208.068 MiB
✅	docker_cluster_agent_arm64	221.314 MiB
✅	docker_cws_instrumentation_amd64	7.447 MiB
✅	docker_cws_instrumentation_arm64	6.877 MiB
✅	docker_dogstatsd_amd64	39.012 MiB
✅	docker_dogstatsd_arm64	37.117 MiB
✅	docker_host_profiler_amd64	305.017 MiB
✅	docker_host_profiler_arm64	316.112 MiB
✅	dogstatsd_deb_amd64	29.747 MiB
✅	dogstatsd_deb_arm64	27.802 MiB
✅	dogstatsd_rpm_amd64	29.747 MiB
✅	dogstatsd_suse_amd64	29.747 MiB
✅	iot_agent_deb_amd64	45.676 MiB
✅	iot_agent_deb_arm64	42.390 MiB
✅	iot_agent_deb_armhf	43.176 MiB
✅	iot_agent_rpm_amd64	45.676 MiB
✅	iot_agent_suse_amd64	45.675 MiB

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: 9ed4fd8c-80c0-4ad8-91da-64a243511fe8

Baseline: de36884
Comparison: 4661a98
Diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	quality_gate_metrics_logs	memory utilization	+0.22	[-0.03, +0.47]	1	Logs bounds checks dashboard
➖	quality_gate_security_no_fs_load	memory utilization	+0.22	[+0.12, +0.31]	1	Logs bounds checks dashboard
➖	quality_gate_security_idle	memory utilization	+0.07	[+0.01, +0.13]	1	Logs bounds checks dashboard
➖	quality_gate_security_mean_fs_load	memory utilization	+0.06	[+0.02, +0.10]	1	Logs bounds checks dashboard
➖	quality_gate_idle_all_features	memory utilization	-0.10	[-0.15, -0.06]	1	Logs bounds checks dashboard
➖	quality_gate_idle	memory utilization	-0.15	[-0.20, -0.10]	1	Logs bounds checks dashboard
➖	quality_gate_logs	% cpu utilization	-1.87	[-2.94, -0.80]	1	Logs bounds checks dashboard

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	observed_value	links
✅	quality_gate_idle	intake_connections	10/10	3 ≤ 4	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	146.66MiB ≤ 154MiB	bounds checks dashboard
✅	quality_gate_idle	total_bytes_received	10/10	581.65KiB ≤ 819.20KiB	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	3 ≤ 4	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	480.31MiB ≤ 495MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	total_bytes_received	10/10	0.89MiB ≤ 1.25MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	180.89MiB ≤ 195MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_logs	total_bytes_received	10/10	264.21MiB ≤ 292MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	328.02 ≤ 2000	bounds checks dashboard
✅	quality_gate_metrics_logs	intake_connections	10/10	3 ≤ 6	bounds checks dashboard
✅	quality_gate_metrics_logs	memory_usage	10/10	395.60MiB ≤ 430MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_metrics_logs	total_bytes_received	10/10	0.86GiB ≤ 1.04GiB	bounds checks dashboard
✅	quality_gate_security_idle	cpu_usage	10/10	30.60 ≤ 40	bounds checks dashboard
✅	quality_gate_security_idle	memory_usage	10/10	296.93MiB ≤ 330MiB	bounds checks dashboard
✅	quality_gate_security_mean_fs_load	cpu_usage	10/10	61.72 ≤ 80	bounds checks dashboard
✅	quality_gate_security_mean_fs_load	memory_usage	10/10	275.96MiB ≤ 310MiB	bounds checks dashboard
✅	quality_gate_security_no_fs_load	cpu_usage	10/10	26.77 ≤ 40	bounds checks dashboard
✅	quality_gate_security_no_fs_load	memory_usage	10/10	281.89MiB ≤ 320MiB	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".

Replicate Execution Details

We run multiple replicates for each experiment/variant. However, we allow replicates to be automatically retried if there are any failures, up to 8 times, at which point the replicate is marked dead and we are unable to run analysis for the entire experiment. We call each of these attempts at running replicates a replicate execution. This section lists all replicate executions that failed due to the target crashing or being oom killed.

Note: In the below tables we bucket failures by experiment, variant, and failure type. For each of these buckets we list out the replicate indexes that failed with an annotation signifying how many times said replicate failed with the given failure mode. In the below example the baseline variant of the experiment named experiment_with_failures had two replicates that failed by oom kills. Replicate 0, which failed 8 executions, and replicate 1 which failed 6 executions, all with the same failure mode.

Experiment	Variant	Replicates	Failure	Logs	Debug Dashboard
experiment_with_failures	baseline	0 (x8) 1 (x6)	Oom killed		Debug Dashboard

The debug dashboard links will take you to a debugging dashboard specifically designed to investigate replicate execution failures.

❌ Retried Profiling Replicate Execution Failures (ddprof)

Note: Profiling replicas may still be executing. See the debug dashboard for up to date status.

Experiment	Variant	Replicates	Failure	Debug Dashboard
quality_gate_idle	baseline	10	Oom killed	Debug Dashboard
quality_gate_idle	comparison	10	Oom killed	Debug Dashboard
quality_gate_idle_all_features	baseline	10	Oom killed	Debug Dashboard
quality_gate_idle_all_features	comparison	10	Oom killed	Debug Dashboard
quality_gate_logs	baseline	10	Oom killed	Debug Dashboard
quality_gate_logs	comparison	10	Oom killed	Debug Dashboard
quality_gate_metrics_logs	baseline	10	Oom killed	Debug Dashboard
quality_gate_metrics_logs	comparison	10	Oom killed	Debug Dashboard
quality_gate_security_idle	baseline	10	Oom killed	Debug Dashboard
quality_gate_security_idle	comparison	10	Oom killed	Debug Dashboard
quality_gate_security_no_fs_load	baseline	10	Oom killed	Debug Dashboard
quality_gate_security_no_fs_load	comparison	10	Oom killed	Debug Dashboard

CI Pass/Fail Decision

✅ Passed. All Quality Gates passed.

• quality_gate_security_mean_fs_load, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_mean_fs_load, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, bounds check total_bytes_received: 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_metrics_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_idle, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_idle, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_security_no_fs_load, bounds check cpu_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_no_fs_load, bounds check memory_usage: 10/10 replicas passed. Gate passed.