Capstone Exercise: Draw the Hub

Start with a blank page, landscape orientation, and draw four horizontal lanes labelled Channels, Hub Core, External Systems, and Books and Control. Place the customer and corporate systems on the far left of the Channels lane, and place SWIFT, Faster Payments, SEPA, Fedwire and CHAPS on the far right of the External Systems lane. Leave generous space in the middle, because the Hub Core lane will hold eighteen components and their connections. Write the payment flow direction at the top of the page, from left to right, and keep that direction consistent for every arrow you draw. Draw the entry half of the hub first, in flow order, and label every arrow with what travels on it. Place Payment Channels, API Gateway, Payment Ingestion Layer, Payment Validation Engine, Enrichment Services, and Sanctions and AML Screening in a row across the Hub Core lane. Draw an arrow from Channels to the Gateway for API traffic, and from Channels to Ingestion for files and messages. Add a branch from Screening to an operations queue for held payments, and a rejection arrow back to the channel for blocked payments. Write the message name on each arrow, such as pain.001 into Ingestion and pacs.008 out of Processing. Draw the decision and execution half next, keeping the same left to right discipline. Place Fraud Detection Engine, Payment Orchestrator, Routing Engine, Payment Processing Engine, Liquidity Management, and Clearing Connectivity after Screening, and draw the Orchestrator as a wide bar above the other five, with vertical arrows showing that it calls each of them in turn. Draw Liquidity Management with a two way arrow to the settlement accounts, and Clearing Connectivity with arrows out to each external rail on the right. Add a small clock icon beside Routing to show cut off times, and a queue symbol beside Processing for retries. Draw the closing half below the main flow, because settlement, books and control run in parallel with execution rather than after it in a single line. Place Settlement Engine, Core Banking Integration, General Ledger, Reconciliation Engine, Exception Management, and Reporting and Audit in a second row inside the Hub Core and Books and Control lanes. Draw Settlement receiving a cleared payment from Clearing Connectivity, Core Banking receiving a posting request from Settlement, and the General Ledger receiving posting events from both. Draw Reconciliation with incoming arrows from the hub, the clearing systems and the bank statements. Add the architecture patterns as annotations, not as extra boxes, so the diagram stays readable. Draw a message queue symbol between Ingestion and Validation, and label it asynchronous with a note that a payroll file of 100,000 payments is queued and processed steadily. Mark the synchronous calls, such as the fraud score and the balance check, with a solid arrow and the word sync. Add a circuit breaker symbol on the arrow to Sanctions Screening, a dead letter queue box beside Processing, and an idempotency key label on the Ingestion box. These annotations show that you understand how the hub behaves, not just what it contains. Finish with a self review against this checklist, and fix every gap before you call the exercise done. Check that all eighteen components appear by name and in flow order, that every arrow is labelled with a message or event name, that the gateway is shown as a front door and not as the hub itself, that Screening, Fraud and Liquidity each have a hold or queue path, and that Settlement, Ledger and Reconciliation form a closed loop with no missing leg. Finally, explain your diagram aloud in under five minutes to a colleague, tracing a 250,000 dollar payment from a corporate API call to a settled pacs.008 and a balanced ledger entry. If you cannot trace it, redraw the missing link.