feat(nats): enable the NATS monitoring HTTP endpoint in the embedded NATS server

[pbleser-oc]

Description

Add configuration options to enable the NATS server HTTP monitoring endpoint:

• NATS_MONITORING_ENABLED (defaults to false)
• NATS_MONITORING_HTTP_HOST (defaults to 127.0.0.1)
• NATS_MONITORING_HTTP_PORT (defaults to 8222)
• NATS_MONITORING_ENABLE_TLS (defaults to false)

Note that, by default, if no configuration changes are made, it does not change the current behaviour: no NATS server monitoring endpoint is enabled nor made available. It requires explicitly enabling it by configuration or environment variable.

Related Issue

• Fixes Enable the NATS monitoring HTTP endpoint in the embedded NATS server #3294

Motivation and Context

See #3294

• allow monitoring tools such as nats-top to inspect consumer stats
• allow Prometheus scraping using prometheus-nats-exporter

How Has This Been Tested?

• start opencloud with NATS_MONITORING_ENABLED set to true
• run nats-top on the same host

To test the Prometheus metrics exporter:

• start opencloud with NATS_MONITORING_ENABLED set to true and NATS_MONITORING_HTTP_HOST set to 0.0.0.0
• start a container of prometheus-nats-exporter as follows:

docker run \
  --add-host host.docker.internal=host-gateway \
  -p 7777:7777 \
  natsio/prometheus-nats-exporter:latest \
  -D -p 7777 \
  -accountz -accstatz -connz_detailed -gatewayz -healthz -leafz -routez -varz \
  http://host.docker.internal:8222

• check the list of metrics exported by the exporter:

curl -sSLf http://localhost:7777/metrics | grep ^gnatsd_

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests only (no source changes)

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation added

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 duplication

Metric	Results
Duplication	0

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🟢 Coverage 0.00% diff coverage · -0.01% coverage variation

Metric	Results
Coverage variation	✅ -0.01% coverage variation (-1.00%)
Diff coverage	✅ 0.00% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (6f5f993)	84041	19349	23.02%
Head commit (cfdb115)	84072 (+31)	19351 (+2)	23.02% (-0.01%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3296)	36	0	0.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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