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2a717a993e
Phase G PR-G3 review identified 5 Critical + 4 High + 5 Medium
findings. This commit lands all 14 fixes plus the optional nits.
CRITICAL
* C1 (cardinality DoS): `service_tier` was read from inbound JSON
and used verbatim as a metric label. A malicious client could
blow up the metric vector unboundedly. Added bounded vocabulary
in `metric_names.rs::service_tier` ({auto, default, flex,
on_demand, priority, scale, other-sentinel}) + a `validate()`
helper. Both request-side (`handlers/responses.rs`) and
response-side (`proxy.rs` Responses arm) gate raw values through
it.
* C2 (dead metric): `proxy_passthrough_bytes_modified_total` had
no production emit site. Wired it in `proxy.rs` to fire when a
dispatcher arm returning `NoCompression`/`Passthrough` produces
a body of a different byte length (a true cache-poisoning
regression detector). The check runs BEFORE the PR-E4
prompt_cache_key injector so legitimate injector mutations do
not trip the alarm.
* C3 (Python/Rust boundary): `proxy_image_generation_call_log_redacted_total`
was a dead Rust counter — the redaction happens entirely in the
Python proxy's request_logger. Removed the Rust counter; moved
the metric to the Python proxy's `/metrics` exporter via the
existing `redactions_total()` module-level counter.
* C4 (Python/Rust boundary): `wrap_rtk_invocations_total` was a
dead Rust counter with no wrap-side bridge. Removed the Rust
counter; added new `headroom/cli/wrap_rtk_metrics.py` with
`record_rtk_invocation(tool, delta)` + `rtk_invocation_counts()`
primitives and surfaced them via the Python proxy's `/metrics`
exporter.
* C5 (dead metric): `proxy_compression_rejected_by_token_check_total`
had no production caller. Wired it in
`live_zone_anthropic.rs`, `live_zone_openai.rs`, and
`live_zone_responses.rs` to increment on every
`BlockAction::RejectedNotSmaller` block in the manifest. The
metric now reflects real "compressor ran but kept original"
cases.
HIGH
* H1 (per-strategy ratio garbage): `proxy_compression_ratio_by_strategy`
emitted the same aggregate ratio for every strategy in
`strategies_applied` when multiple strategies ran on one body.
Added `per_strategy_tokens: Vec<PerStrategyTokens>` to
`Outcome::Compressed`; per-strategy `(before, after)` is
accumulated from the manifest at the wrapper sites and emitted
one sample per strategy in `proxy.rs`. Empty vec → fallback to
one aggregate-labelled sample with a debug log (Phase E
normalization paths that don't track per-strategy tokens).
* H2 (aborted stream): cache_hit_rate observed on client
disconnects mid-stream. Added a gate: Anthropic only fires when
`state.status == MessageStop`, OpenAI Responses only when
`terminal_status().is_some()`. Extracted the gate into the
pure function `compute_anthropic_session_hit_rate(state)` so
the H2 contract is unit-testable independent of the shared
global registry.
* H3 (docs lie + alarm contract): docs claimed HELP/TYPE is
reachable on fresh boot, then contradicted itself. Force-zero
every counter / gauge MetricVec with an `__init__` sentinel
label on each scrape so HELP/TYPE + a zero row are visible from
boot. Histograms are NOT force-zeroed (a synthetic observe(0.0)
would pollute percentiles). PromQL queries in docs filter
`{... != "__init__"}` so the sentinel rows are excluded from
aggregations.
* H4 (crate-version dependency): pinned `prometheus = "=0.13.4"`
exactly (no caret) so a future minor bump cannot silently break
the H3 force-zero contract that relies on this crate's gather()
semantics. Added a clear "retest the alarm contract on bump"
paragraph in docs.
MEDIUM
* M1 (saturate on cached > input): OpenAI Chat + Responses cache-
hit-rate computed `non_cached = input.saturating_sub(cached)`,
silently clamping to 0 if `cached > input`. Per "no silent
fallbacks", log + skip the emit on this wire-format pathology.
* M2 (over-fire on non-image base64): Python redactor's "density
heuristic" over-fired on encrypted blobs / signed tokens /
minified JSON / tool outputs. Tightened: only redact strings
inside known image-bearing JSON paths (`data`, `url`,
`image_url`, `image`) OR strings starting with `data:image/`.
* M3 (NaN clamp): cache_hit_rate::observe used `f64::clamp(0,1)`
which returns NaN for NaN input; the `debug_assert!` was
compiled out in release. Added `is_finite()` guard with a
loud-log + skip before observe.
* M4 (PromQL median-only): added p95, p99, mean (sum/count), and
Phase H canary-gate query section to docs. Canary fails if ANY
of {p50, p95, p99, mean} regresses below the Python baseline.
* M5 (label byte vs char): the `<image:base64-redacted bytes=N>`
placeholder reported character count, not UTF-8 byte count.
Switched to `.encode('utf-8').__len__()` so the label is
honest for non-ASCII payloads (ASCII base64 still has byte ==
char so existing scrapes are unchanged).
OPTIONAL
* Removed dead `debug_assert_eq!(buffered.len(), buffered.len(),
...)` no-op in proxy.rs.
* Normalised `record_response_status` log level from `info` to
`debug` to match peer metric helpers.
Tests:
* Rust: 11 integration_metrics tests (was 6) + 9 cache_hit_rate
unit tests (was 4) + 2 compression_ratio (unchanged). New
coverage: service_tier known/unknown bucketing, C2 alarm wire,
H1 per-strategy ratio, H2 abort gate, M3 NaN/inf skip.
* Python: 27 tests (was 13). New coverage: M2 path-gated
redaction, M5 byte vs char label, wrap_rtk_metrics primitive
thread safety and validation.
`cargo fmt --check`, `cargo clippy --workspace -- -D warnings`,
`cargo test -p headroom-proxy --lib` (221 passed) and the
integration_metrics + integration_compression +
integration_volatile_detector + integration_cache_control +
integration_cache_drift + integration_responses +
integration_bedrock_metrics test files all green. Full
`cargo test --workspace` deferred — disk pressure during the
agent session left insufficient space for the linker to write
the full integration test artifacts; runs that did fit all
passed. `make ci-precheck` deferred for the same reason.
ruff check + ruff format + mypy headroom/proxy/request_logger.py
+ headroom/cli/wrap_rtk_metrics.py + headroom/proxy/prometheus_metrics.py
green.
274 lines
12 KiB
Markdown
274 lines
12 KiB
Markdown
# Observability — proxy metrics
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The Headroom Rust proxy exposes Prometheus-format metrics on the
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`/metrics` endpoint of every running proxy instance. The metric
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catalogue below covers Phase D (Bedrock route instrumentation) and
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Phase G PR-G3 (per-invocation RTK + proxy-wide observability).
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All metric names + label keys are constants in
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`crates/headroom-proxy/src/observability/metric_names.rs`, so any
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rename catches one file in code review.
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## Metric catalogue
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### Bedrock route (Phase D PR-D3)
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `bedrock_invoke_count_total` | Counter | `model`, `region`, `auth_mode` | One increment per Bedrock `/invoke` or `/converse` request. |
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| `bedrock_invoke_latency_seconds` | Histogram | `model`, `region` | Latency from proxy entry to upstream completion. Buckets target 50ms–60s. |
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| `bedrock_eventstream_message_count_total` | Counter | `model`, `region`, `event_type` | One increment per parsed binary EventStream message. |
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### Proxy-wide (Phase G PR-G3)
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#### Cache + compression
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `proxy_cache_hit_rate_per_session` | Histogram | `provider` | Per-session cache hit rate. **Phase H canary gate.** |
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| `proxy_compression_ratio_by_strategy` | Histogram | `strategy`, `content_type` | `compressed_tokens / original_tokens` per shrunk block. |
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| `proxy_compression_rejected_by_token_check_total` | Counter | `strategy` | Compressor ran but failed the shrink check. |
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#### Cache-safety alarm
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `proxy_passthrough_bytes_modified_total` | Counter | `path` | Bytes mutated on a passthrough path. **Must stay 0 outside the compression hot path** — any non-zero rate fires the cache-safety alarm. |
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The alarm metric is wired in `crates/headroom-proxy/src/proxy.rs`:
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when the dispatcher returns `Outcome::NoCompression` or
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`Outcome::Passthrough`, the post-dispatcher byte length is compared
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to the original buffered length and any delta increments the
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counter (by the byte delta) under the request's path label. The
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PR-E4 prompt_cache_key injector runs AFTER the alarm check, so its
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intentional byte mutations do not trip the alarm.
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#### Upstream rate limits
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `proxy_rate_limit_remaining_requests` | Gauge | `provider` | Last-seen remaining requests in the current window. |
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| `proxy_rate_limit_remaining_tokens` | Gauge | `provider` | Last-seen remaining tokens in the current window. |
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| `proxy_rate_limit_remaining_input_tokens` | Gauge | `provider` | Anthropic-only input-token bucket. |
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| `proxy_rate_limit_remaining_output_tokens` | Gauge | `provider` | Anthropic-only output-token bucket. |
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#### OpenAI Responses telemetry
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `proxy_service_tier_count_total` | Counter | `tier` | Service-tier distribution observed at the proxy. |
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| `proxy_response_status_count_total` | Counter | `status` | Terminal status distribution (`completed`, `incomplete`, `failed`, `cancelled`, `in_progress`). |
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#### Wrap CLI / RTK (Python-side)
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `wrap_rtk_invocations_total` | Counter | `tool` | RTK invocations observed via the wrap-CLI tail. Surfaced via the Python proxy's `/metrics` exporter; the wrap CLI bumps `headroom.cli.wrap_rtk_metrics.record_rtk_invocation(...)`. |
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> **C4 remediation:** This counter is Python-side because RTK is
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> wrapped by `headroom wrap` (Python CLI) and the wrap-side tail
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> is the natural emit site. The Rust proxy previously held a dead
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> counter for this metric; that has been removed.
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#### Image log redaction (Python-side)
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| Name | Type | Labels | Purpose |
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|------|------|--------|---------|
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| `proxy_image_generation_call_log_redacted_total` | Counter | _none_ | Base64-encoded image payloads redacted from request logs. Driven from `headroom.proxy.request_logger.redactions_total()`. |
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> **C3 remediation:** Image redaction is purely a Python-proxy
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> operation (the request logger walks JSON and replaces over-
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> threshold image payloads with placeholders). The counter lives
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> Python-side so we have one source of truth instead of two. The
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> Rust proxy previously held a dead counter for this metric; that
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> has been removed.
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## How to query
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The proxy renders Prometheus text-format on `GET /metrics`:
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```bash
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curl -s http://127.0.0.1:8787/metrics
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```
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### Phase H canary gate
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The canary script that decides "ship Rust, retire Python" uses
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**all four** of these queries against `proxy_cache_hit_rate_per_session`
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to confirm parity vs the Python baseline. A single percentile is
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not enough — a regression that only shows up at the tail (a small
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class of long sessions losing cache hits) would slip through a
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median-only check.
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```promql
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# p50, p95, p99 of cache hit rate over the last 5 minutes, per provider.
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histogram_quantile(0.50, sum by (provider, le) (rate(proxy_cache_hit_rate_per_session_bucket{provider!="__init__"}[5m])))
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histogram_quantile(0.95, sum by (provider, le) (rate(proxy_cache_hit_rate_per_session_bucket{provider!="__init__"}[5m])))
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histogram_quantile(0.99, sum by (provider, le) (rate(proxy_cache_hit_rate_per_session_bucket{provider!="__init__"}[5m])))
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# Mean cache hit rate over the last 5 minutes, per provider. The
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# `sum / count` form is the cleanest "average without a quantile"
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# query and is what the Python baseline reports.
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sum by (provider) (rate(proxy_cache_hit_rate_per_session_sum{provider!="__init__"}[5m]))
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/
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sum by (provider) (rate(proxy_cache_hit_rate_per_session_count{provider!="__init__"}[5m]))
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```
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The canary fails if ANY of `p50`, `p95`, `p99`, or `mean` regresses
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below the Python baseline for any provider over the canary window.
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### Other common queries
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```promql
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# Cache-safety alarm. Should always be 0 (post-`__init__` row).
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sum(rate(proxy_passthrough_bytes_modified_total{path!="__init__"}[5m]))
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# Per-strategy compression value at p50 (post-H1 fix: each strategy
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# reports its own before/after; pre-fix this was the same aggregate
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# ratio repeated per strategy).
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histogram_quantile(0.50, sum by (strategy, le) (rate(proxy_compression_ratio_by_strategy_bucket{strategy!="__init__"}[1h])))
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# Per-strategy compression value at p95 and p99 (catch outlier
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# strategies that fail to shrink at the tail).
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histogram_quantile(0.95, sum by (strategy, le) (rate(proxy_compression_ratio_by_strategy_bucket{strategy!="__init__"}[1h])))
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histogram_quantile(0.99, sum by (strategy, le) (rate(proxy_compression_ratio_by_strategy_bucket{strategy!="__init__"}[1h])))
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# Strategies that ran but failed the token-check (compressor ran
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# but its output was not strictly smaller, so the original was
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# kept). High rate here means the compressor needs tuning.
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sum by (strategy) (rate(proxy_compression_rejected_by_token_check_total{strategy!="__init__"}[1h]))
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# Upstream rate-limit headroom (smaller = closer to throttle).
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proxy_rate_limit_remaining_tokens{provider="anthropic"}
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# RTK invocation rate (Python-side).
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sum by (tool) (rate(wrap_rtk_invocations_total{tool!="__init__"}[5m]))
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# Image-redaction rate (Python-side).
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rate(proxy_image_generation_call_log_redacted_total[5m])
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```
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All queries above include a `{... != "__init__"}` filter so the
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sentinel zero-rows the boot-touch contract emits do not skew the
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result. See "Wiring → H3 force-zero" below.
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## Wiring
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Every metric registration is `OnceLock`-backed and lazy: the first
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call to a `*_counter()` / `*_gauge()` / `*_histogram()` helper
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registers the family with the shared registry. `handle_metrics`
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force-touches every Phase G PR-G3 family before scraping.
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### H3 force-zero
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The `prometheus` crate v0.13 skips empty MetricVecs from `gather()`
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entirely — neither HELP/TYPE lines nor rows appear until the
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family has been incremented at least once with a label tuple.
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Operators expect to see the catalogue from boot, so
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`handle_metrics` increments each counter / gauge MetricVec by 0
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under a sentinel `__init__` label tuple before the first scrape.
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HELP/TYPE then surface from boot and dashboards/alarms see a
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predictable scrape shape.
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Counters with the `__init__` label increment by 0, so the
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alarm-able "must stay 0" semantic of
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`proxy_passthrough_bytes_modified_total` is preserved (the family
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becomes visible, the rate stays 0). PromQL queries should filter
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`{... != "__init__"}` so the sentinel rows are excluded from
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aggregations (the catalogue above does this).
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Histograms are NOT force-zeroed: a synthetic `observe(0.0)` would
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contribute a real sample to the per-label distribution and pollute
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percentile readings. The two histogram families
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(`proxy_cache_hit_rate_per_session` and
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`proxy_compression_ratio_by_strategy`) only surface in the scrape
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after the first real session, by design.
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### H4 prometheus crate version pin
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The H3 contract above relies on the `prometheus` crate's v0.13
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`gather()` semantics — empty MetricVec families are omitted from
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the scrape. **This is implementation-defined behaviour.** If
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`crates/headroom-proxy/Cargo.toml` ever bumps the `prometheus`
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dependency, retest the alarm contract:
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1. Start a fresh proxy.
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2. `curl /metrics` and confirm every counter / gauge family has
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HELP/TYPE + an `__init__` row.
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3. Confirm histograms (`*_cache_hit_rate_per_session`,
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`*_compression_ratio_by_strategy`) DO NOT appear (no
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`observe()` calls yet).
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4. Drive one cache-hit session, scrape again, confirm histograms
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now appear.
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5. Confirm `passthrough_bytes_modified_total` stays at 0 across
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passthrough requests.
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The crate version is pinned exactly (`= "0.13.4"`, no caret) in
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`Cargo.toml` precisely so a silent semver bump cannot break the
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contract without a code-review trigger.
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### C2 alarm wiring
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`proxy_passthrough_bytes_modified_total` fires from `proxy.rs` when
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a dispatcher arm that promised byte-equal passthrough
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(`Outcome::NoCompression` or `Outcome::Passthrough`) produces a
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final body of a different byte length. The check runs BEFORE the
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PR-E4 prompt_cache_key injector so the injector's intentional byte
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mutations do not trip the alarm.
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### H1 per-strategy ratio wiring
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`proxy_compression_ratio_by_strategy` samples one observation per
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strategy using the strategy's OWN before/after token counts
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(plumbed through `Outcome::Compressed.per_strategy_tokens` from
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the manifest in `live_zone_anthropic` / `live_zone_openai` /
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`live_zone_responses`). Pre-H1 the same aggregate ratio was
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emitted per strategy when multiple strategies ran on one body,
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making Phase H per-strategy dashboards read garbage.
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### H2 aborted-stream gate
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The `proxy_cache_hit_rate_per_session` histogram observes ONLY
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when the SSE stream completed:
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* Anthropic: `state.status == StreamStatus::MessageStop` after the
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channel closes.
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* OpenAI Chat: `state.usage.is_some()` (the final usage chunk only
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arrives at stream completion).
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* OpenAI Responses: `state.terminal_status().is_some()`.
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A client disconnect mid-stream closes the channel without setting
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the terminal flag — under H2 we log + skip rather than observe a
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garbage half-stream sample.
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## Cardinality discipline
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Every label vocabulary is bounded by code, not customer input:
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- `model` / `region`: read from path params + `Config::bedrock_region`.
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- `auth_mode`: 3-variant enum (`payg`, `oauth`, `subscription`).
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- `provider`: 3 values (`anthropic`, `openai_chat`, `openai_responses`).
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- `strategy`: `&'static str` from the compressor's `BlockAction::Compressed`.
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- `content_type`: `&'static str` from `headroom_core::transforms::ContentType`.
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- `tier`: validated through
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`crate::observability::metric_names::service_tier::validate(raw: &str)`.
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Returns one of `{auto, default, flex, on_demand, priority, scale}`
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or the sentinel `"other"` for anything else. **The raw inbound
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value is never used as a label.** A malicious client posting
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`{"service_tier":"<random>"}` per request gets bucketed to
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`"other"` and a `tracing::warn!` is emitted so wire-format drift
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surfaces loudly in logs.
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- `status`: 5-variant enum.
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- `tool` (Python-side `wrap_rtk_invocations_total`): bounded by the
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set of tools the wrap CLI rewrites, captured by
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`headroom.cli.wrap_rtk_metrics`.
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There is no code path where a malicious client can drive label
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cardinality unbounded.
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## See also
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- `docs/rtk-architecture.md` — why RTK lives wrap-side, not proxy-side.
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- `crates/headroom-proxy/src/observability/` — implementation.
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- `REALIGNMENT/09-phase-G-rtk-observability.md` — spec.
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- `REALIGNMENT/10-phase-H-python-retirement.md` — H1 acceptance gate.
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