Define the session purpose
Separate market-data, order-routing and drop-copy requirements where applicable. Each session should have a documented owner and expected message flow.
Counterparty specification
Implement against the counterparty’s FIX specification rather than assuming all FIX integrations behave identically. Record required tags, custom fields and supported message types.
Session management
Plan sequence handling, reconnect behavior, heartbeats, logon credentials and recovery after disconnects.
Security
Protect credentials and network access, restrict administrative changes and keep production secrets out of source code and browser-delivered applications.
Certification
Build a repeatable certification test plan covering normal orders, rejects, cancels, partial fills, disconnects and recovery.
Monitoring
Track session state, sequence issues, reject rates, response times and message-processing failures.
Operational handover
Document contacts, restart procedures, log locations, known counterparty behavior and escalation paths.