[Backport 7.78.x] [CONS-8194] Fix panic when advanced dispatching is disabled while KSM Core cluster check is enabled

[dd-octo-sts]

Backport 56ac038 from #48700.

---

What does this PR do?

Fixes the following panic when DD_CLUSTER_CHECKS_ADVANCED_DISPATCHING_ENABLED is set to false while the KSM core check runs as a cluster check.

Clone: #48494

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x2443644]

goroutine 1722 [running]:
github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks.(*ksmShardingManager).isEnabled(...)
        github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks/ksm_sharding.go:43
github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks.(*dispatcher).scheduleKSMCheck(_, {{0x4000856150, 0x15}, {0x4001310150, 0x1, 0x1}, {0x0, 0x0, 0x0}, {0x0, ...}, ...})
        github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks/dispatcher_ksm.go:18 +0x24
github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks.(*dispatcher).Schedule(0x4001650a80, {0x4000a26108?, 0x4001a85eb0?, 0xd?})
        github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks/dispatcher_main.go:176 +0x220
github.com/DataDog/datadog-agent/comp/core/autodiscovery/scheduler.(*Controller).Register(0x40008fb4a0, {0x361ec8c, 0xd}, {0x3cb1650, 0x4001650a80}, 0x1)
        github.com/DataDog/datadog-agent/comp/core/autodiscovery/scheduler/controller.go:125 +0x388
github.com/DataDog/datadog-agent/comp/core/autodiscovery/autodiscoveryimpl.(*AutoConfig).AddScheduler(0x400150c798?, {0x361ec8c?, 0x40013ab080?}, {0x3cb1650?, 0x4001650a80?}, 0xd0?)
        github.com/DataDog/datadog-agent/comp/core/autodiscovery/autodiscoveryimpl/autoconfig.go:604 +0x2c
github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks.(*Handler).runDispatch(0x4001650b00, {0x3cd23a8, 0x40004a2fa0})
        github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks/handler.go:163 +0x50
created by github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks.(*Handler).Run in goroutine 635
        github.com/DataDog/datadog-agent/pkg/clusteragent/clusterchecks/handler.go:137 +0x2fc

Motivation

CONS-8194

Describe how you validated your changes

Was able to reproduce this with cluster agent versions 7.74.0+ possibly due to this change: a59c26a

Wrote tests to ensure that it does not run into nil errors when advanced dispatching is disabled.

Additional notes

With this change, I believe KSM Resource Type sharding will require advanced dispatching to be enabled.

[agent-platform-auto-pr]

Files inventory check summary

File checks results against ancestor 9486d535:

Results for datadog-agent_7.78.0~rc.5.git.1.c38737b.pipeline.105389979-1_amd64.deb:

No change detected

[agent-platform-auto-pr]

Static quality checks

✅ Please find below the results from static quality gates
Comparison made with ancestor 9486d53
📊 Static Quality Gates Dashboard
🔗 SQG Job

31 successful checks with minimal change (< 2 KiB)

	Quality gate	Current Size
✅	agent_deb_amd64	752.429 MiB
✅	agent_deb_amd64_fips	709.302 MiB
✅	agent_heroku_amd64	314.364 MiB
✅	agent_msi	605.931 MiB
✅	agent_rpm_amd64	752.412 MiB
✅	agent_rpm_amd64_fips	709.285 MiB
✅	agent_rpm_arm64	730.816 MiB
✅	agent_rpm_arm64_fips	690.722 MiB
✅	agent_suse_amd64	752.412 MiB
✅	agent_suse_amd64_fips	709.285 MiB
✅	agent_suse_arm64	730.816 MiB
✅	agent_suse_arm64_fips	690.722 MiB
✅	docker_agent_amd64	812.735 MiB
✅	docker_agent_arm64	815.906 MiB
✅	docker_agent_jmx_amd64	1003.651 MiB
✅	docker_agent_jmx_arm64	995.600 MiB
✅	docker_cluster_agent_amd64	205.398 MiB
✅	docker_cluster_agent_arm64	219.740 MiB
✅	docker_cws_instrumentation_amd64	7.142 MiB
✅	docker_cws_instrumentation_arm64	6.689 MiB
✅	docker_dogstatsd_amd64	39.230 MiB
✅	docker_dogstatsd_arm64	37.445 MiB
✅	dogstatsd_deb_amd64	29.874 MiB
✅	dogstatsd_deb_arm64	28.027 MiB
✅	dogstatsd_rpm_amd64	29.874 MiB
✅	dogstatsd_suse_amd64	29.874 MiB
✅	iot_agent_deb_amd64	43.257 MiB
✅	iot_agent_deb_arm64	40.304 MiB
✅	iot_agent_deb_armhf	41.052 MiB
✅	iot_agent_rpm_amd64	43.258 MiB
✅	iot_agent_suse_amd64	43.258 MiB

On-wire sizes (compressed)

	Quality gate	Change	Size (prev → curr → max)
✅	agent_deb_amd64	+33.59 KiB (0.02% increase)	174.710 → 174.743 → 178.360
✅	agent_deb_amd64_fips	-22.39 KiB (0.01% reduction)	165.288 → 165.266 → 172.790
✅	agent_heroku_amd64	+3.94 KiB (0.01% increase)	75.061 → 75.065 → 79.970
✅	agent_msi	-12.0 KiB (0.01% reduction)	138.410 → 138.398 → 146.220
✅	agent_rpm_amd64	-2.09 KiB (0.00% reduction)	177.345 → 177.343 → 181.830
✅	agent_rpm_amd64_fips	-33.73 KiB (0.02% reduction)	167.424 → 167.392 → 173.370
✅	agent_rpm_arm64	+2.79 KiB (0.00% increase)	159.336 → 159.339 → 163.060
✅	agent_rpm_arm64_fips	-19.42 KiB (0.01% reduction)	151.354 → 151.335 → 156.170
✅	agent_suse_amd64	-2.09 KiB (0.00% reduction)	177.345 → 177.343 → 181.830
✅	agent_suse_amd64_fips	-33.73 KiB (0.02% reduction)	167.424 → 167.392 → 173.370
✅	agent_suse_arm64	+2.79 KiB (0.00% increase)	159.336 → 159.339 → 163.060
✅	agent_suse_arm64_fips	-19.42 KiB (0.01% reduction)	151.354 → 151.335 → 156.170
✅	docker_agent_amd64	-3.16 KiB (0.00% reduction)	267.991 → 267.988 → 272.480
✅	docker_agent_arm64	neutral	255.176 MiB → 261.060
✅	docker_agent_jmx_amd64	neutral	336.637 MiB → 341.100
✅	docker_agent_jmx_arm64	neutral	319.809 MiB → 325.620
✅	docker_cluster_agent_amd64	neutral	71.964 MiB → 72.920
✅	docker_cluster_agent_arm64	neutral	67.534 MiB → 68.220
✅	docker_cws_instrumentation_amd64	neutral	2.999 MiB → 3.330
✅	docker_cws_instrumentation_arm64	neutral	2.729 MiB → 3.090
✅	docker_dogstatsd_amd64	neutral	15.171 MiB → 15.820
✅	docker_dogstatsd_arm64	neutral	14.484 MiB → 14.830
✅	dogstatsd_deb_amd64	neutral	7.889 MiB → 8.790
✅	dogstatsd_deb_arm64	neutral	6.776 MiB → 7.710
✅	dogstatsd_rpm_amd64	neutral	7.901 MiB → 8.800
✅	dogstatsd_suse_amd64	neutral	7.901 MiB → 8.800
✅	iot_agent_deb_amd64	-3.41 KiB (0.03% reduction)	11.399 → 11.396 → 12.040
✅	iot_agent_deb_arm64	-2.07 KiB (0.02% reduction)	9.700 → 9.698 → 10.450
✅	iot_agent_deb_armhf	neutral	9.937 MiB → 10.620
✅	iot_agent_rpm_amd64	neutral	11.412 MiB → 12.060
✅	iot_agent_suse_amd64	neutral	11.412 MiB → 12.060

[cit-pr-commenter-54b7da]

Regression Detector

Regression Detector Results

Metrics dashboard
Target profiles
Run ID: d7f583a9-158f-46c0-9a13-9caf04954682

Baseline: 9486d53
Comparison: c38737b
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	+0.97	[-2.09, +4.04]	1	Logs

Fine details of change detection per experiment

perf	experiment	goal	Δ mean %	Δ mean % CI	trials	links
➖	docker_containers_cpu	% cpu utilization	+0.97	[-2.09, +4.04]	1	Logs
➖	otlp_ingest_logs	memory utilization	+0.74	[+0.65, +0.83]	1	Logs
➖	otlp_ingest_metrics	memory utilization	+0.35	[+0.19, +0.50]	1	Logs
➖	ddot_logs	memory utilization	+0.33	[+0.27, +0.39]	1	Logs
➖	docker_containers_memory	memory utilization	+0.31	[+0.24, +0.38]	1	Logs
➖	quality_gate_idle_all_features	memory utilization	+0.11	[+0.07, +0.15]	1	Logs bounds checks dashboard
➖	uds_dogstatsd_20mb_12k_contexts_20_senders	memory utilization	+0.08	[+0.02, +0.14]	1	Logs
➖	ddot_metrics_sum_cumulativetodelta_exporter	memory utilization	+0.07	[-0.16, +0.29]	1	Logs
➖	file_to_blackhole_1000ms_latency	egress throughput	+0.05	[-0.39, +0.48]	1	Logs
➖	ddot_metrics_sum_delta	memory utilization	+0.03	[-0.13, +0.20]	1	Logs
➖	file_to_blackhole_0ms_latency	egress throughput	+0.03	[-0.45, +0.51]	1	Logs
➖	uds_dogstatsd_to_api_v3	ingress throughput	-0.00	[-0.20, +0.19]	1	Logs
➖	tcp_dd_logs_filter_exclude	ingress throughput	-0.00	[-0.11, +0.11]	1	Logs
➖	uds_dogstatsd_to_api	ingress throughput	-0.01	[-0.20, +0.19]	1	Logs
➖	file_to_blackhole_100ms_latency	egress throughput	-0.02	[-0.10, +0.05]	1	Logs
➖	quality_gate_idle	memory utilization	-0.03	[-0.08, +0.02]	1	Logs bounds checks dashboard
➖	file_tree	memory utilization	-0.04	[-0.10, +0.01]	1	Logs
➖	file_to_blackhole_500ms_latency	egress throughput	-0.06	[-0.45, +0.33]	1	Logs
➖	ddot_metrics	memory utilization	-0.17	[-0.34, +0.00]	1	Logs
➖	ddot_metrics_sum_cumulative	memory utilization	-0.25	[-0.39, -0.11]	1	Logs
➖	quality_gate_metrics_logs	memory utilization	-1.00	[-1.23, -0.76]	1	Logs bounds checks dashboard
➖	tcp_syslog_to_blackhole	ingress throughput	-1.03	[-1.16, -0.90]	1	Logs
➖	quality_gate_logs	% cpu utilization	-2.05	[-3.57, -0.53]	1	Logs bounds checks dashboard

Bounds Checks: ✅ Passed

perf	experiment	bounds_check_name	replicates_passed	observed_value	links
✅	docker_containers_cpu	simple_check_run	10/10	721 ≥ 26
✅	docker_containers_memory	memory_usage	10/10	278.90MiB ≤ 370MiB
✅	docker_containers_memory	simple_check_run	10/10	705 ≥ 26
✅	file_to_blackhole_0ms_latency	memory_usage	10/10	0.19GiB ≤ 1.20GiB
✅	file_to_blackhole_0ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_1000ms_latency	memory_usage	10/10	0.23GiB ≤ 1.20GiB
✅	file_to_blackhole_1000ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_100ms_latency	memory_usage	10/10	0.19GiB ≤ 1.20GiB
✅	file_to_blackhole_100ms_latency	missed_bytes	10/10	0B = 0B
✅	file_to_blackhole_500ms_latency	memory_usage	10/10	0.22GiB ≤ 1.20GiB
✅	file_to_blackhole_500ms_latency	missed_bytes	10/10	0B = 0B
✅	quality_gate_idle	intake_connections	10/10	3 = 3	bounds checks dashboard
✅	quality_gate_idle	memory_usage	10/10	174.07MiB ≤ 175MiB	bounds checks dashboard
✅	quality_gate_idle_all_features	intake_connections	10/10	2 ≤ 3	bounds checks dashboard
✅	quality_gate_idle_all_features	memory_usage	10/10	490.65MiB ≤ 550MiB	bounds checks dashboard
✅	quality_gate_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_logs	memory_usage	10/10	204.05MiB ≤ 220MiB	bounds checks dashboard
✅	quality_gate_logs	missed_bytes	10/10	0B = 0B	bounds checks dashboard
✅	quality_gate_metrics_logs	cpu_usage	10/10	349.00 ≤ 2000	bounds checks dashboard
✅	quality_gate_metrics_logs	intake_connections	10/10	4 ≤ 6	bounds checks dashboard
✅	quality_gate_metrics_logs	memory_usage	10/10	407.06MiB ≤ 475MiB	bounds checks dashboard
✅	quality_gate_metrics_logs	missed_bytes	10/10	0B = 0B	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_idle_all_features, bounds check intake_connections: 10/10 replicas passed. Gate passed.
• quality_gate_idle_all_features, 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 intake_connections: 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 memory_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 cpu_usage: 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.