feat(o11y): outgoing fetch metrics (counter + histogram)

[nicacioliveira]

What

Adds always-on metrics for outgoing HTTP fetches:

• outgoing_fetch counter — total calls by app, host, method, status
• outgoing_fetch_duration histogram (ms) — latency by app, host, method, status

Uses host only (not path) to keep cardinality low.

Queries

# Calls/s to VTEX
rate(outgoing_fetch_total{host=~".*vtex.*"}[5m])

# P95 latency by host
histogram_quantile(0.95, rate(outgoing_fetch_duration_bucket[5m]))

# Compare sites with/without Redis
rate(outgoing_fetch_total{app="vtex"}[5m]) by (service)

Always on, no env var needed. Log-based outgoing fetch remains off by default (OTEL_LOG_OUTGOING_FETCH=true).

---

Summary by cubic

Adds metrics for outgoing HTTP fetches to track request volume and latency with low-cardinality labels. Disabled by default; enable with OTEL_METRICS_OUTGOING_FETCH=true.

• New Features
  • outgoing_fetch counter: counts requests by app, host, method, status.
  • outgoing_fetch_duration histogram (ms): records latency with the same labels.
  • Uses host only (no path) to keep cardinality low.
  • Log-based outgoing fetch remains off unless OTEL_LOG_OUTGOING_FETCH=true.

^{Written for commit 994e7dc. Summary will update on new commits.}

Summary by CodeRabbit

• New Features
  • Added optional outgoing network-request telemetry (configurable via environment) that captures request counts and response-duration histograms.
  • Collected attributes include destination host, application identifier, HTTP method, and response status (defaults to "unknown" when absent), enabling richer visibility into external request performance.

[github-actions]

Tagging Options

Should a new tag be published when this PR is merged?

• 👍 for Patch 1.191.3 update
• 🎉 for Minor 1.192.0 update
• 🚀 for Major 2.0.0 update

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: c1818c5c-5501-4696-9dc6-a4b982f634ef

📥 Commits

Reviewing files that changed from the base of the PR and between 6b80866 and 994e7dc.

📒 Files selected for processing (1)

• observability/otel/metrics.ts

🚧 Files skipped from review as they are similar to previous changes (1)

• observability/otel/metrics.ts

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📝 Walkthrough

Walkthrough

Optional OpenTelemetry metrics added to record outgoing fetches: an outgoing_fetch counter and outgoing_fetch_duration histogram. An onFetch callback extracts app/host/method/status attributes and records count and duration (ms) for each fetch when OTEL_METRICS_OUTGOING_FETCH === "true".

Changes

Cohort / File(s)	Summary
Fetch Telemetry Metrics observability/otel/metrics.ts	Adds optional outgoing-fetch telemetry gated by OTEL_METRICS_OUTGOING_FETCH === "true". Registers onFetch callback that parses destination host from event.url, builds attributes { app, host, method, status } (defaults to "unknown"), increments outgoing_fetch counter and records event.durationMs to outgoing_fetch_duration histogram (unit "ms").

Sequence Diagram(s)

sequenceDiagram
    participant Fetch as "Outgoing Fetch"
    participant Handler as "onFetch Handler"
    participant Metrics as "OTel Metrics SDK"
    participant Exporter as "OTel Exporter"

    Fetch->>Handler: emit fetch event (url, method, status, durationMs)
    Handler->>Handler: parse host, normalize attributes (app, host, method, status)
    Handler->>Metrics: increment outgoing_fetch counter (attributes)
    Handler->>Metrics: record outgoing_fetch_duration histogram (durationMs, attributes)
    Metrics->>Exporter: export metrics batch

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Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Suggested reviewers

• igoramf

Poem

🐰 I hopped through code on nimble feet,

Counting fetches, timing each beat.
Hosts and methods I softly note,
So telemetry sings from every moat. 🥕

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat(o11y): outgoing fetch metrics (counter + histogram)' directly and clearly describes the main change: adding observability metrics for outgoing fetches with specific metric types.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/outgoing-fetch-metrics

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[cubic-dev-ai]

No issues found across 1 file

[cubic-dev-ai]

1 issue found across 1 file (changes from recent commits).

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="observability/otel/metrics.ts">

<violation number="1" location="observability/otel/metrics.ts:71">
P1: Outgoing fetch metrics are now gated by `OTEL_METRICS_OUTGOING_FETCH`, which disables the feature by default instead of keeping it always-on.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}

[cubic-dev-ai]

P1: Outgoing fetch metrics are now gated by OTEL_METRICS_OUTGOING_FETCH, which disables the feature by default instead of keeping it always-on.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At observability/otel/metrics.ts, line 71:

<comment>Outgoing fetch metrics are now gated by `OTEL_METRICS_OUTGOING_FETCH`, which disables the feature by default instead of keeping it always-on.</comment>

<file context>
@@ -64,10 +64,12 @@ if (OTEL_IS_ENABLED) {
 import { ValueType } from "../../deps.ts";
 import { onFetch, parseUrlParts } from "../../utils/patched_fetch.ts";
 
+if (Deno.env.get("OTEL_METRICS_OUTGOING_FETCH") === "true") {
+
 const fetchCount = meter.createCounter("outgoing_fetch", {
</file context>