Measure end-to-end latency
Instrument feed dissemination, network transit, decoding, book updates, strategy evaluation, risk checks, encoding, outbound transit, gateway handling, and matching. Use consistent clocks and analyze tail percentiles under message bursts, not only an average in a quiet lab.
Set a maximum event age. An old decision should be rejected even when the local book still looks plausible. Tail latency is often more dangerous than a slightly slower median.
Defend the market state
Incremental feeds require sequence checks, snapshot synchronization, gap recovery, and validation. A missing update can produce a believable but wrong book. Affected routes should stop until state is rebuilt according to venue procedure.
When queues grow, processing every obsolete event can be worse than rebuilding from a fresh snapshot. Data validity is a gate, not a confidence feature that can be outweighed by a large spread.
Keep the hot path deterministic
The hot path receives validated state, computes a candidate, applies cached policy, constructs an order, and sends. Research models, dashboards, and expensive explanations can operate outside it and publish versioned parameters. This limits unpredictable pauses and simplifies replay.
Pre-trade checks still cover instrument, side, quantity, price, notional, position, credit, and message rate. Independent gateways and venue controls provide layers when strategy logic fails.
Recover ambiguous order state
Acknowledgments, partial fills, cancel races, and timeouts require explicit state machines. A timeout is unknown, not failed. Use client identifiers, reserve working balances, query venue state after restart, and prioritize hedges and cancellations during uncertainty.
Inventory-aware thresholds can favor trades that restore balance. Venue balances remain counterparty exposure even when no order is open, so speed does not replace concentration limits or rebalancing.
Test shutdown and replay
Record event streams for deterministic replay. Inject gaps, delays, rejects, duplicate messages, late fills, rate limits, and disconnections. Verify the resulting positions and control events. Performance tests should include risk and telemetry at peak load.
Global and scoped kill switches must be exercised. Measure time to stop new orders, cancel working orders, and expose residual positions. Reactivation requires reconciliation and explicit authorization.