Immutable event log and workflow execution traces that make every automation run inspectable and recoverable -- the operational infrastructure that separates a production automation system from a prototype.
Event log structure: every incoming event stored in an append-only events table (event_id UUID, source_system, event_type, payload_hash, received_at, processing_status). The payload stored as JSONB in PostgreSQL with the original content preserved exactly as received, even if the event ultimately fails processing. Events are never deleted from the log; a retention policy moves records older than 90 days to cold storage (S3 with Glacier lifecycle policy) while maintaining the metadata record for search.
Workflow execution trace: each workflow run creates an execution record (execution_id, event_id, workflow_id, started_at, completed_at, status). Each step within the execution creates a step record (step_id, execution_id, step_name, input_payload, output_payload, started_at, completed_at, attempt_count, status). When a workflow step fails, the trace shows exactly which step failed, the input it was given, the error response from the destination system, and the number of retry attempts. Investigation starts from a complete record, not from log searching.
Replay capability: individual event replay from the event log admin interface -- the original event payload is resubmitted to the workflow router as if it arrived fresh, without triggering the original source system webhook again. Idempotency keys ensure that replaying an event that previously succeeded partially (e.g., CRM record created but email not sent) only re-executes the failed steps, not the already-completed ones. Bulk replay: an admin query selects a time range or event type (e.g., all deal.won events between 2024-01-10 and 2024-01-12 that have status='failed') and submits them to the replay queue for reprocessing -- used when a workflow bug is fixed and all affected events need retroactive reprocessing.
Monitoring and alerting: workflow failure rate tracked as a daily metric; PagerDuty alert if failure rate exceeds 5% in any 1-hour window; Slack notification for any event that exhausts all retry attempts and lands in the DLQ; weekly summary email to the operations owner showing total events processed, success rate, and top failure categories by event type and workflow.