feat: prometheus metrics endpoint - #37
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adds --metrics-port flag to enable a prometheus HTTP endpoint on a
separate port. when enabled, the server records:
- ember_connections_active / total / rejected (gauge/counters)
- ember_commands_total{cmd} (counter per command)
- ember_commands_duration_seconds{cmd} (histogram, cache-latency buckets)
- ember_commands_errors_total{cmd} (counter)
- ember_keys_total, ember_memory_used_bytes (gauges, polled every 5s)
- ember_keys_expired_total, ember_keys_evicted_total (gauges from shard stats)
zero overhead when --metrics-port is not set — no recorder installed,
timing code is gated behind a bool.
also adds Command::command_name() for zero-allocation metric labels
and enriches KeyspaceStats with cumulative expiry/eviction counters.
kacy
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Feb 11, 2026
feat: prometheus metrics endpoint
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summary
--metrics-port <port>CLI flag to expose a prometheus HTTP endpoint on a separate portShardRequest::Statsand publishes key/memory/expiry/eviction gaugesCommand::command_name()returning&'static strfor zero-allocation metric labelsKeyspaceStatswith cumulativekeys_expiredandkeys_evictedcounters--metrics-portis not set — no recorder installed, all timing gated behind a booltested
cargo test --workspace— all 216 tests passcargo clippy --workspace -- -D warnings— clean--metrics-port 9100, confirmedcurl localhost:9100/metricsreturns prometheus output with all expected metric familiesdesign considerations
metrics,metrics-exporter-prometheus) are only inember-server.ember-corestays dependency-free — the stats poller pulls data through the existing shard broadcast mechanismcommand_name()method avoids allocation by returning static strings, suitable for use as prometheus labels