Visual workflow automation builder and engine

Problem

The client's follow-up system could only send reminders at fixed offsets, so it could not express rules like messaging people who watched more than half a webinar differently from those who missed it.

Solution

The team started with an SRS and architecture pack covering the workflow JSON schema, node catalogue, timing semantics, API surface and database schema, which the client approved. It built the visual builder inside the client's existing Pug and vanilla JavaScript codebase using JointJS, with drag and drop, connectors, zoom, pan, minimap, validation and draft and publish versioning. Behind it, a queue-backed engine on BullMQ and Redis with MongoDB change-stream listeners runs the full webinar trigger catalogue, delayed and wait-until jobs, deduplication and idempotency, and email and SMS through SendGrid and Twilio with merge fields. Conditional branching added named branches with an automatic else branch, AND/OR segments and recursive nesting, with a per-registrant evaluation engine.

Key features

• Drag-and-drop workflow canvas with zoom, pan, minimap and auto-fit
• Webinar triggers: registration, start and end, attended, missed, watch percentage, replay viewed, days after and custom events
• Email and SMS actions with merge fields
• Delay and wait-until-event nodes
• If/else conditions with multiple named branches, AND/OR logic and nesting
• Validation that blocks publishing on errors and warns on gaps
• Draft and publish versioning
• Queue-backed execution with per-node status, deduplication and idempotency

Tech stack

• API authentication middleware
• BullMQ
• Celery
• Docker
• Express
• FastAPI
• GitHub
• JavaScript
• JointJS
• MongoDB
• MongoDB change streams
• Mongoose
• Node.js
• Pug
• Redis
• SendGrid
• Tuleap
• Twilio
• sequential-workflow-designer