core: add some very basic metrics

pyproject.toml

@@ -34,6 +34,7 @@ dependencies = [
     "aiohttp>=3.11.0,<4",
     "cryptography>=46.0.0",
     "numpy>=2.0.0,<3",
+    "prometheus-client>=0.21.0,<1",
 ]
 
 [project.license]

src/lean_spec/subspecs/api/server.py

@@ -1,9 +1,10 @@
 """
-API server for checkpoint sync and node status endpoints.
+API server for checkpoint sync, node status, and metrics endpoints.
 
 Provides HTTP endpoints for:
 - /lean/states/finalized - Serve finalized checkpoint state as SSZ
 - /health - Health check endpoint
+- /metrics - Prometheus metrics endpoint
 
 This matches the checkpoint sync API implemented in zeam.
 """
@@ -18,6 +19,8 @@
 
 from aiohttp import web
 
+from lean_spec.subspecs.metrics import generate_metrics
+
 if TYPE_CHECKING:
     from lean_spec.subspecs.forkchoice import Store
 
@@ -34,6 +37,14 @@ async def _handle_health(_request: web.Request) -> web.Response:
     return web.json_response({"status": "healthy", "service": "lean-spec-api"})
 
 
+async def _handle_metrics(_request: web.Request) -> web.Response:
+    """Handle Prometheus metrics endpoint."""
+    return web.Response(
+        body=generate_metrics(),
+        content_type="text/plain; version=0.0.4; charset=utf-8",
+    )
+
+
 @dataclass(frozen=True, slots=True)
 class ApiServerConfig:
     """Configuration for the API server."""
@@ -87,6 +98,7 @@ async def start(self) -> None:
         app.add_routes(
             [
                 web.get("/health", _handle_health),
+                web.get("/metrics", _handle_metrics),
                 web.get("/lean/states/finalized", self._handle_finalized_state),
             ]
         )

src/lean_spec/subspecs/metrics/__init__.py

@@ -0,0 +1,44 @@
+"""
+Metrics module for observability.
+
+Provides counters, gauges, and histograms for tracking consensus client behavior.
+Exposes metrics in Prometheus text format.
+"""
+
+from .registry import (
+    REGISTRY,
+    attestations_invalid,
+    attestations_produced,
+    attestations_received,
+    attestations_valid,
+    block_processing_time,
+    blocks_processed,
+    blocks_proposed,
+    current_slot,
+    finalized_slot,
+    generate_metrics,
+    head_slot,
+    justified_slot,
+    peers_connected,
+    reorgs,
+    validators_count,
+)
+
+__all__ = [
+    "REGISTRY",
+    "attestations_invalid",
+    "attestations_produced",
+    "attestations_received",
+    "attestations_valid",
+    "block_processing_time",
+    "blocks_processed",
+    "blocks_proposed",
+    "current_slot",
+    "finalized_slot",
+    "generate_metrics",
+    "head_slot",
+    "justified_slot",
+    "peers_connected",
+    "reorgs",
+    "validators_count",
+]

src/lean_spec/subspecs/metrics/registry.py

@@ -0,0 +1,140 @@
+"""
+Metric registry using prometheus_client.
+
+Provides pre-defined metrics for a consensus client.
+Exposes metrics in Prometheus text format via the /metrics endpoint.
+"""
+
+from __future__ import annotations
+
+from prometheus_client import (
+    CollectorRegistry,
+    Counter,
+    Gauge,
+    Histogram,
+    generate_latest,
+)
+
+# Create a dedicated registry for lean-spec metrics.
+#
+# Using a dedicated registry avoids pollution from default Python process metrics.
+REGISTRY = CollectorRegistry()
+
+# -----------------------------------------------------------------------------
+# Node Information
+# -----------------------------------------------------------------------------
+
+head_slot = Gauge(
+    "lean_head_slot",
+    "Current head slot",
+    registry=REGISTRY,
+)
+
+current_slot = Gauge(
+    "lean_current_slot",
+    "Current time slot",
+    registry=REGISTRY,
+)
+
+justified_slot = Gauge(
+    "lean_justified_slot",
+    "Latest justified slot",
+    registry=REGISTRY,
+)
+
+finalized_slot = Gauge(
+    "lean_finalized_slot",
+    "Latest finalized slot",
+    registry=REGISTRY,
+)
+
+validators_count = Gauge(
+    "lean_validators_count",
+    "Active validators",
+    registry=REGISTRY,
+)
+
+# -----------------------------------------------------------------------------
+# Block Processing
+# -----------------------------------------------------------------------------
+
+blocks_processed = Counter(
+    "lean_blocks_processed_total",
+    "Total blocks processed",
+    registry=REGISTRY,
+)
+
+block_processing_time = Histogram(
+    "lean_block_processing_seconds",
+    "Block processing duration",
+    buckets=(0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 2.5),
+    registry=REGISTRY,
+)
+
+# -----------------------------------------------------------------------------
+# Attestations
+# -----------------------------------------------------------------------------
+
+attestations_received = Counter(
+    "lean_attestations_received_total",
+    "Total attestations received",
+    registry=REGISTRY,
+)
+
+attestations_valid = Counter(
+    "lean_attestations_valid_total",
+    "Valid attestations",
+    registry=REGISTRY,
+)
+
+attestations_invalid = Counter(
+    "lean_attestations_invalid_total",
+    "Invalid attestations",
+    registry=REGISTRY,
+)
+
+# -----------------------------------------------------------------------------
+# Network
+# -----------------------------------------------------------------------------
+
+peers_connected = Gauge(
+    "lean_peers_connected",
+    "Connected peers",
+    registry=REGISTRY,
+)
+
+# -----------------------------------------------------------------------------
+# Consensus Events
+# -----------------------------------------------------------------------------
+
+reorgs = Counter(
+    "lean_reorgs_total",
+    "Chain reorganizations",
+    registry=REGISTRY,
+)
+
+# -----------------------------------------------------------------------------
+# Validator Production
+# -----------------------------------------------------------------------------
+
+blocks_proposed = Counter(
+    "lean_blocks_proposed_total",
+    "Blocks proposed by this node",
+    registry=REGISTRY,
+)
+
+attestations_produced = Counter(
+    "lean_attestations_produced_total",
+    "Attestations produced by this node",
+    registry=REGISTRY,
+)
+
+
+def generate_metrics() -> bytes:
+    """
+    Generate Prometheus metrics output.
+
+    Returns:
+        Prometheus text format output as bytes.
+    """
+    return generate_latest(REGISTRY)

src/lean_spec/subspecs/sync/service.py

@@ -41,6 +41,7 @@
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING
 
+from lean_spec.subspecs import metrics
 from lean_spec.subspecs.chain.clock import SlotClock
 from lean_spec.subspecs.containers import Block, SignedBlockWithAttestation
 from lean_spec.subspecs.containers.attestation import SignedAttestation
@@ -203,12 +204,24 @@ def _process_block_wrapper(
         # Delegate to the actual block processor (typically Store.on_block).
         #
         # The processor validates the block and updates forkchoice state.
-        new_store = self.process_block(store, block)
+        with metrics.block_processing_time.time():
+            new_store = self.process_block(store, block)
 
         # Track metrics after successful processing.
         #
         # We only count blocks that pass validation and update the store.
         self._blocks_processed += 1
+        metrics.blocks_processed.inc()
+
+        # Update chain state metrics.
+        metrics.head_slot.set(float(new_store.blocks[new_store.head].slot))
+        metrics.justified_slot.set(float(new_store.latest_justified.slot))
+        metrics.finalized_slot.set(float(new_store.latest_finalized.slot))
+
+        # Update validator count from head state.
+        head_state = new_store.states.get(new_store.head)
+        if head_state is not None:
+            metrics.validators_count.set(float(len(head_state.validators)))
 
         # Persist block and state to database if available.
         #

src/lean_spec/subspecs/validator/service.py

@@ -29,6 +29,7 @@
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING
 
+from lean_spec.subspecs import metrics
 from lean_spec.subspecs.chain.clock import SlotClock
 from lean_spec.subspecs.chain.config import SECONDS_PER_INTERVAL
 from lean_spec.subspecs.containers import (
@@ -184,6 +185,7 @@ async def _maybe_produce_block(self, slot: Slot) -> None:
                 # Create signed block wrapper for publishing.
                 signed_block = self._sign_block(block, validator_index, signatures)
                 self._blocks_produced += 1
+                metrics.blocks_proposed.inc()
 
                 # Emit the block for network propagation.
                 await self.on_block(signed_block)
@@ -217,6 +219,7 @@ async def _produce_attestations(self, slot: Slot) -> None:
             # Sign the attestation using our secret key.
             signed_attestation = self._sign_attestation(attestation_data, validator_index)
             self._attestations_produced += 1
+            metrics.attestations_produced.inc()
 
             # Emit the attestation for network propagation.
             await self.on_attestation(signed_attestation)