Designing Workflow Engine Architecture
1. Designing State Machine Architecture
| Element | Detail |
|---|---|
| States | Finite, named |
| Transitions | Triggered by events |
| Guards / actions | Conditions and side effects |
| Tools | Spring Statemachine, XState, AWS Step Functions |
| Visualization | Diagrams from spec |
2. Designing Workflow Orchestration
| Tool | Strength |
|---|---|
| Temporal | Durable execution; code-based |
| Cadence | Uber predecessor of Temporal |
| Camunda / Zeebe | BPMN; visual |
| AWS Step Functions | JSON state language |
| Argo Workflows | K8s-native |
| Conductor (Netflix) | JSON DAG |
3. Designing Long-Running Workflow Management
| Aspect | Detail |
|---|---|
| Durable state | Survive process restarts |
| Timers | Sleep days/months reliably |
| Signals | External events into running workflow |
| Queries | Read state without disturbing |
4. Designing Workflow Versioning
| Approach | Detail |
|---|---|
| Version constants | If/else by GetVersion (Temporal) |
| Run new workflows on new version | Old runs finish on old |
| Activity backwards-compat | Add fields, don't break |
| Migrations | Special workflow to convert state |
5. Designing Compensation and Rollback
| Pattern | Detail |
|---|---|
| Saga compensation | Per-step undo logic |
| Try-Confirm/Cancel | TCC pattern |
| Outbox | Reliable side-effect events |
| Idempotency | Compensations safe to retry |
6. Designing Workflow State Persistence
| Mechanism | Detail |
|---|---|
| Event sourcing | History of decisions/results |
| Replay | Reconstruct state on worker restart |
| Snapshots | Compress long histories |
| Storage | Cassandra / MySQL / Postgres |
7. Designing Workflow Monitoring
| Signal | Detail |
|---|---|
| Per-step duration | Find slow stages |
| Failure rate | Per workflow / activity |
| In-flight count | Backlog |
| Stuck detection | Long time in one state |
| UI | Temporal Web, Camunda Cockpit |
8. Designing Human-in-the-Loop Workflows
| Element | Detail |
|---|---|
| Task queue | Pending human tasks |
| Assignment / claim | To role / user |
| Reminders / SLA | Escalate if overdue |
| Approval chains | Sequential / parallel |
9. Designing Parallel Task Execution
| Pattern | Detail |
|---|---|
| Fan-out / fan-in | Map → join |
| Dynamic parallel | Count from input |
| Bounded concurrency | Cap parallelism |
| First-of-N | Take fastest result |
10. Designing Workflow Scheduling
| Mechanism | Detail |
|---|---|
| Cron schedules | Recurring |
| Delayed start | Run at future time |
| Catchup / overlap policy | Skip / queue / allow |
| Calendar-aware | Skip weekends/holidays |
11. Designing Workflow Error Handling
| Strategy | Detail |
|---|---|
| Retry policy | Per-activity backoff |
| Non-retryable | Mark certain errors as terminal |
| Compensation on failure | Saga rollback |
| Dead workflow queue | Manual intervention |
12. Designing Workflow Templates
| Approach | Detail |
|---|---|
| Reusable subflows | Compose workflows |
| Parameterized | Inputs at start |
| Library | Common patterns (approval, ETL) |
| Versioned templates | Track changes |