fix(serverless-init): attach per-instance tag to MicroVM enhanced usage metric

[litianningdatadog]

Motivation

Codex flagged this on PR #53093 (review comment): MicroVM's enhanced usage metric (aws.lambda.microvm.instance) is emitted with the same static tag set for every MicroVM booted from a given image.

MicroVM.GetEnhancedMetricTags computes the Usage tag set once at startup — before the MicroVM's instance ID is known, since the platform only reveals it via the /run lifecycle hook — and nothing ever updates it afterward. Under normal autoscaling, with multiple concurrent MicroVMs running from the same image, their periodic usage samples are indistinguishable from one another: instance-level usage collapses into a single series.

Solution

The obvious fix — mutate the frozen tag set on ServerlessMetricAgent once /run reveals the instance ID, mirroring the existing LogsTagSetter/TraceTagSetter pattern — turned out to require a lock/atomic on ServerlessMetricAgent. That struct is passed by value into CloudService.Shutdown across every cloud service (AppService, CloudRun, CloudRunJobs, ContainerApp, LocalService, MicroVM), so adding any lock-bearing field trips go vet's copylocks check everywhere, not just for MicroVM.

Instead, this attaches the tag at the point of emission rather than mutating shared state:

• lifecycle.Server already tracks the instance ID race-free (instanceID *atomic.String, captured in handleRun). Added InstanceID(), a nil-safe accessor, so callers outside the lifecycle package can read it.
• MicroVM.CurrentUsageMetricTags() turns that into an "instance:<id>" tag, or nil before /run has fired.
• enhancedmetrics.Collector gained an optional usageMetricTagsFunc, invoked on every collection tick and passed straight through the existing AddEnhancedUsageMetric(..., extraTags ...string) parameter — no new shared mutable state needed.
• main.go duck-types cloudService against a local usageMetricTagProvider interface to wire this hook. Every other cloud service doesn't implement it, so usageMetricTagsFunc stays nil for them and their usage metrics are unaffected.

This keeps the change scoped to MicroVM plus small, nil-safe, additive plumbing in the shared collector — no other cloud service, ServerlessMetricAgent, or the Shutdown interface needed to change.

Test plan

• dda inv test --targets=./cmd/serverless-init/... — all 281 tests pass (12 new: InstanceID() nil/before/after /run, CurrentUsageMetricTags() nil-server/before-run/after-run end-to-end, collector dynamic-tag forwarding + nil-func regression guard, NewCollector wiring, and the usageMetricTagProvider type-assertion pinning *MicroVM in vs. every other cloud service out)
• gofmt -l clean on all changed files
• dda inv linter.go --targets=./cmd/serverless-init/... — 0 issues
• cmd/serverless-init/enhanced-metrics/collector.go/collector_test.go carry a pre-existing //go:build linux tag; this session ran on macOS without a Linux cross-toolchain, so those specific new tests are syntax-checked (gofmt -e) and reviewed but not yet executed — first real run will be in Linux CI

🤖 Generated with Claude Code

[dd-octo-sts]

Static quality checks

✅ Please find below the results from static quality gates
Comparison made with ancestor 1f54e07
📊 Static Quality Gates Dashboard
🔗 SQG Job

33 successful checks with minimal change (< 2 KiB)

	Quality gate	Current Size
✅	agent_deb_amd64	750.599 MiB
✅	agent_deb_amd64_fips	705.387 MiB
✅	agent_heroku_amd64	307.504 MiB
✅	agent_msi	639.379 MiB
✅	agent_rpm_amd64	750.583 MiB
✅	agent_rpm_amd64_fips	705.370 MiB
✅	agent_rpm_arm64	727.261 MiB
✅	agent_rpm_arm64_fips	685.184 MiB
✅	agent_suse_amd64	750.583 MiB
✅	agent_suse_amd64_fips	705.370 MiB
✅	agent_suse_arm64	727.261 MiB
✅	agent_suse_arm64_fips	685.184 MiB
✅	docker_agent_amd64	809.275 MiB
✅	docker_agent_arm64	810.989 MiB
✅	docker_agent_jmx_amd64	1000.173 MiB
✅	docker_agent_jmx_arm64	990.539 MiB
✅	docker_cluster_agent_amd64	209.843 MiB
✅	docker_cluster_agent_arm64	222.890 MiB
✅	docker_cws_instrumentation_amd64	7.439 MiB
✅	docker_cws_instrumentation_arm64	6.877 MiB
✅	docker_dogstatsd_amd64	39.228 MiB
✅	docker_dogstatsd_arm64	37.368 MiB
✅	docker_host_profiler_amd64	303.231 MiB
✅	docker_host_profiler_arm64	314.740 MiB
✅	dogstatsd_deb_amd64	29.968 MiB
✅	dogstatsd_deb_arm64	28.012 MiB
✅	dogstatsd_rpm_amd64	29.968 MiB
✅	dogstatsd_suse_amd64	29.968 MiB
✅	iot_agent_deb_amd64	46.141 MiB
✅	iot_agent_deb_arm64	42.833 MiB
✅	iot_agent_deb_armhf	43.601 MiB
✅	iot_agent_rpm_amd64	46.142 MiB
✅	iot_agent_suse_amd64	46.141 MiB

[dd-octo-sts]

Files inventory check summary

File checks results against ancestor 1f54e07e:

Results for datadog-agent_7.83.0~devel.git.330.e54ecc4.pipeline.126330100-1_amd64.deb:

No change detected

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: 08e2fac1-f929-48d1-acf3-2ba575e40673

Baseline: 1f54e07
Comparison: e54ecc4
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	+0.84	[+0.60, +1.09]	1	Logs bounds checks dashboard
➖	quality_gate_security_idle	memory utilization	+0.20	[+0.14, +0.25]	1	Logs bounds checks dashboard
➖	quality_gate_idle	memory utilization	+0.15	[+0.10, +0.20]	1	Logs bounds checks dashboard
➖	quality_gate_security_mean_fs_load	memory utilization	+0.14	[+0.10, +0.17]	1	Logs bounds checks dashboard
➖	quality_gate_security_no_fs_load	memory utilization	+0.02	[-0.07, +0.11]	1	Logs bounds checks dashboard
➖	quality_gate_private_action_runner	memory utilization	-0.20	[-0.32, -0.08]	1	Logs bounds checks dashboard
➖	quality_gate_idle_all_features	memory utilization	-0.69	[-0.73, -0.64]	1	Logs bounds checks dashboard
➖	quality_gate_logs	% cpu utilization	-1.89	[-2.88, -0.89]	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	148.18MiB ≤ 154MiB	bounds checks dashboard
✅	quality_gate_idle	total_bytes_received	10/10	738.12KiB ≤ 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	494.55MiB ≤ 495MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	total_bytes_received	10/10	1.13MiB ≤ 1.25MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	184.06MiB ≤ 195MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_logs	total_bytes_received	10/10	264.16MiB ≤ 292MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	374.85 ≤ 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	415.45MiB ≤ 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	0.93GiB ≤ 1.04GiB	bounds checks dashboard
✅	quality_gate_private_action_runner	memory_usage	10/10	71.30MiB ≤ 75MiB	bounds checks dashboard
✅	quality_gate_security_idle	cpu_usage	10/10	31.16 ≤ 100	bounds checks dashboard
✅	quality_gate_security_idle	memory_usage	10/10	301.84MiB ≤ 330MiB	bounds checks dashboard
✅	quality_gate_security_mean_fs_load	cpu_usage	10/10	64.07 ≤ 200	bounds checks dashboard
✅	quality_gate_security_mean_fs_load	memory_usage	10/10	275.56MiB ≤ 310MiB	bounds checks dashboard
✅	quality_gate_security_no_fs_load	cpu_usage	10/10	23.08 ≤ 100	bounds checks dashboard
✅	quality_gate_security_no_fs_load	memory_usage	10/10	284.92MiB ≤ 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_all_features	baseline	10	Oom killed	Debug Dashboard
quality_gate_idle_all_features	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	Crashed (exit code: 134)	Debug Dashboard
quality_gate_security_idle	comparison	10	Crashed (exit code: 134)	Debug Dashboard
quality_gate_security_no_fs_load	baseline	10	Crashed (exit code: 134)	Debug Dashboard
quality_gate_security_no_fs_load	comparison	10	Crashed (exit code: 134)	Debug Dashboard

CI Pass/Fail Decision

✅ Passed. All Quality Gates 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_private_action_runner, bounds check memory_usage: 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 missed_bytes: 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 intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_metrics_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_idle, bounds check intake_connections: 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 memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check missed_bytes: 10/10 replicas passed. Gate passed.
• quality_gate_logs, bounds check total_bytes_received: 10/10 replicas passed. Gate passed.
• quality_gate_security_mean_fs_load, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_mean_fs_load, bounds check cpu_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_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_security_no_fs_load, bounds check memory_usage: 10/10 replicas passed. Gate passed.
• quality_gate_security_no_fs_load, bounds check cpu_usage: 10/10 replicas passed. Gate passed.

[Lewis-E]

There's probably a good reason none of the other origin mappings have tests? This is all basically just a restatement of the code. There's no complexity to catch issues in here.

[litianningdatadog]

The change was introduced in #53030

[Copilot]

Pull request overview

This PR fixes enhanced usage metric cardinality for AWS Lambda MicroVM by attaching a per-instance tag (instance:<id>) at emission time once the /run hook reveals the MicroVM instance ID, avoiding shared mutable state changes to the metric agent.

Changes:

• Expose lifecycle.Server.InstanceID() as a nil-safe accessor for the captured MicroVM instance ID.
• Add an optional usageMetricTagsFunc hook to enhancedmetrics.Collector and forward its dynamic tags into AddEnhancedUsageMetric.
• Wire the hook in main.go via a local usageMetricTagProvider interface, implemented by *cloudservice.MicroVM, plus targeted unit tests.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
cmd/serverless-init/main.go	Duck-types cloud service to optionally provide dynamic usage metric tags; passes hook into enhanced metrics collector.
cmd/serverless-init/main_test.go	Adds interface-conformance/negative assertions for usageMetricTagProvider wiring.
cmd/serverless-init/lifecycle/server.go	Adds exported, nil-safe InstanceID() accessor for instance ID captured from /run.
cmd/serverless-init/lifecycle/server_test.go	Adds coverage for InstanceID() behavior before/after /run and on nil receiver.
cmd/serverless-init/enhanced-metrics/collector.go	Adds usageMetricTagsFunc to collector and forwards its output as extra tags on each usage metric emission.
cmd/serverless-init/enhanced-metrics/collector_unsupported.go	Updates non-Linux stub constructor signature to match the new API.
cmd/serverless-init/enhanced-metrics/collector_test.go	Adds tests for dynamic-tag forwarding, nil hook behavior, and constructor wiring.
cmd/serverless-init/cloudservice/microvm.go	Implements CurrentUsageMetricTags() to provide the per-instance instance:<id> tag once available.
cmd/serverless-init/cloudservice/microvm_test.go	Adds end-to-end tests for CurrentUsageMetricTags() nil/before-run/after-run behavior and interface guard.

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