Event-driven order processing on AWS

# yaml-language-server: $schema=../references/diagram.schema.json
title: Event-driven order processing on AWS
subtitle: One Amazon EventBridge bus fans order events out to an AWS Step Functions workflow, an Amazon SQS billing queue and an Amazon SNS topic
direction: down
# merge: false gives the dashed fan-outs from the bus and from the SNS topic their own ports
# instead of one shared trunk each.
layout: { merge: false }

legend:
  solid: Numbered order path
  dashed: Other rule targets and subscribers

groups:
  cloud: { type: aws:cloud }
  region: { type: aws:region, label: us-east-1, in: cloud }
  workflow: { type: aws:step-functions, label: AWS Step Functions workflow, in: region }

nodes:
  customers: { icon: aws:users, label: Customers }
  api: { icon: aws:api-gateway, label: Orders API, note: "Amazon API Gateway, POST /orders", in: region }
  bus: { icon: aws:eventbridge-custom-event-bus, label: Orders event bus, note: Amazon EventBridge, in: region }
  reserve: { icon: aws:lambda, label: Reserve stock, note: AWS Lambda, in: workflow }
  charge: { icon: aws:lambda, label: Charge payment, note: AWS Lambda, in: workflow }
  ship: { icon: aws:lambda, label: Create shipment, note: AWS Lambda, in: workflow }
  table: { icon: aws:dynamodb-table, label: Orders table, note: Amazon DynamoDB, in: region }
  billing: { icon: aws:simple-queue-service-queue, label: Billing queue, note: Amazon SQS queue, in: region }
  invoice: { icon: aws:lambda, label: Invoice generator, note: AWS Lambda, in: region }
  notices: { icon: aws:simple-notification-service-topic, label: Order notifications, note: Amazon SNS topic, in: region }
  email: { icon: aws:simple-notification-service-email-notification, label: Email subscription, in: region }
  analytics: { icon: aws:simple-queue-service-queue, label: Analytics queue, note: Amazon SQS queue, in: region }

edges:
  # The numbered path is the main story. EventBridge invokes every target asynchronously, so
  # dashed marks the other rule targets and subscribers, not a different delivery mode.
  - customers -> api: { step: 1 }
  - api -> bus: { label: OrderPlaced, step: 2 }
  - bus -> workflow: { label: fulfillment rule, step: 3 }
  # constraint: false keeps the three workflow steps side by side in one row instead of three rows.
  - { from: reserve, to: charge, constraint: false }
  - { from: charge, to: ship, constraint: false }
  - workflow -> table: { label: order status, step: 4 }
  - bus --> billing: billing rule
  - billing --> invoice
  - bus --> notices: notification rule
  - notices --> email, analytics