# Loan Broker Showcases


## Loan Broker showcase

The Loan Broker showcase is a basic loan broker implementation following the [structure presented](https://www.enterpriseintegrationpatterns.com/patterns/messaging/ComposedMessagingExample.html) by [Gregor Hohpe](https://www.enterpriseintegrationpatterns.com/gregor.html) in his book, [_Enterprise Integration Patterns_](https://www.enterpriseintegrationpatterns.com/).

![Logical architecture of the loan broker](consumerloanbroker-logicalview.gif)

The Loan Broker showcase demonstrates how to build distributed systems with NServiceBus and the Particular Service Platform. It's available in two flavors, one for AWS and one for Azure, each using equivalent cloud services for messaging, persistence, and hosting.

The [AWS Loan Broker showcase](https://github.com/Particular/AwsLoanBrokerShowcase) uses [AWS SQS and SNS](/transports/sqs/index.md) for message queueing and event publishing, [DynamoDB](/persistence/dynamodb/index.md) for [saga](/nservicebus/sagas/index.md) data persistence, and [Lambda functions](/nservicebus/hosting/aws-lambda-simple-queue-service/index.md) to host some of the loan broker components.

The [Azure Loan Broker showcase](https://github.com/Particular/AzureLoanBrokerShowcase) uses [Azure Service Bus](/transports/azure-service-bus/index.md) for message queueing and event publishing, [SQL Server](/persistence/sql/index.md) for [saga](/nservicebus/sagas/index.md) data persistence, and [Azure Functions](/nservicebus/hosting/azure/functions/index.md) to host some of the loan broker components.

Here's an overview of the solution:

```mermaid
flowchart LR
    Client[["Client endpoint<br/><small>Sends the request</small>"]]
    FindBestLoan(["FindBestLoan<br/><small>Command</small>"])

    CreditBureau["Credit bureau API<br/><small>Serverless, HTTP call</small>"]
    SagaStore[("Saga persistence<br/><small>SQL Server, DynamoDB, etc.<small>")]

    subgraph Broker["LoanBrokerSaga manages the loan request"]
        direction TB
        Enrich["Enrichment handler<br/><small>Adds credit score</small>"]
        Decide["LoanBrokerSaga<br/><small>Decides which banks to ask</small>"]
        Enrich --> Decide
    end

    QuoteRequested(["QuoteRequested<br/><small>Event, published by saga</small>"])

    BankA[["Bank A endpoint<br/><small>Subscriber queue</small>"]]
    BankB[["Bank B endpoint<br/><small>Subscriber queue</small>"]]
    BankC[["Bank C endpoint<br/><small>Subscriber queue</small>"]]
    HandlerA["QuoteHandler<br/><small>Outbox-backed</small>"]
    HandlerB["QuoteHandler<br/><small>Outbox-backed</small>"]
    HandlerC["QuoteHandler<br/><small>Outbox-backed</small>"]

    LoanQuoteSubmitted(["Bank responses<br/><small>Reply, based on bank process</small>"])
    LoanQuotesReady(["LoanQuotesReady<br/><small>Event, saga completes</small>"])

    ClientReceives[["Client endpoint<br/><small>Receives the result</small>"]]
    Notifications[["Notifications endpoint<br/><small>Sends email</small>"]]

    Client --> FindBestLoan --> Enrich
    CreditBureau <--> Enrich
    SagaStore <--> Decide
    Decide --> QuoteRequested
    QuoteRequested --> BankA --> HandlerA
    QuoteRequested --> BankB --> HandlerB
    QuoteRequested --> BankC --> HandlerC
    HandlerA --> LoanQuoteSubmitted
    HandlerB --> LoanQuoteSubmitted
    HandlerC --> LoanQuoteSubmitted
    LoanQuoteSubmitted --> Decide
    Decide --> LoanQuotesReady
    LoanQuotesReady --> ClientReceives
    LoanQuotesReady --> Notifications

    classDef endpoint fill:#64748b,stroke:#334155,color:#fff
    classDef command fill:#d97706,stroke:#92400e,color:#fff
    classDef event fill:#0d9488,stroke:#115e59,color:#fff
    classDef external fill:#dc6e4f,stroke:#9a3412,color:#fff
    classDef broker fill:#6d28d9,stroke:#4c1d95,color:#fff

    class Client,ClientReceives,Notifications,BankA,BankB,BankC,HandlerA,HandlerB,HandlerC,Enrich,Decide endpoint
    class FindBestLoan,LoanQuoteSubmitted command
    class QuoteRequested,LoanQuotesReady event
    class CreditBureau,SagaStore external
    style Broker fill:#f3e8ff,stroke:#6d28d9,stroke-width:2px
```

The showcase is composed of:

- A client application sends loan requests.
- A credit bureau provides the customers' credit scores.
- A loan broker service receives loan requests, enriches them with credit scores, and orchestrates communication with downstream banks.
- Three bank adapters, acting like Anti-Corruption layers (ACL), simulate communication with downstream banks offering loans.
- An email sender simulates email communication with customers.

The example also ships the following monitoring services:

- The Particular platform to monitor endpoints, capture and visualize audited messages, and manage failed messages.
- A Prometheus instance to collect, store, and query raw metrics data.
- A Grafana instance with three different metrics dashboards using Prometheus as the data source.
- A Jaeger instance to visualize OpenTelemetry traces.
- AWS Distro for OpenTelemetry collector (ADOT) to collect and export metrics and traces to various destinations.

### Repositories

- [AWS Loan Broker Showcase](https://github.com/Particular/AwsLoanBrokerShowcase)
- [Azure Loan Broker Showcase](https://github.com/Particular/AzureLoanBrokerShowcase)