F# Scrum onion architecture sample

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This sample focuses on applying functional constructs over cluing together libraries and frameworks. It substitutes .NET dependency injection container, FluentValidation, MediatR, Entity Framework, Moq, Respawn, and a migration tool for custom constructs.

It's imperative shell, functional core illustrated. Specifically, Program.fs and Infrastructure.fs make up the shell while Application.fs and Domain.fs make up the core.

Where F# shines is in the core and IntegrationTest.fs. The shell is similar in nature to many C# applications.

The sample includes the following features:

• REST API adhering to the Zalando API guidelines with JWTs supporting role-based security.
• A simple identity provider to issue, renew, and inspect JWTs accepted by the REST API.
• Command Query Responsibility Segregation (CQRS) access to the application layer.
• Paged responses for endpoints which return collections.
• Integration tests with the ability to fake any dependency.
• Database migrations and initial seeding.
• ASP.NET health checks for memory and database.
• k6 load test with baseline under tests/k6.
• Architecture decision records under docs/architecture-decision-records.

The Scrum domain was chosen because everyone is familiar with it, though most aspects of the application is illustrated with stories and tasks only. Onion architecture and domain driven design may therefore seem to introduce a disproportional amount of complexity. In practice, they're only worth it for larger, more complex domains with more integrations.

Not every project requires an implementation of every concept from onion architecture and domain driven design. Concepts should be scaled up or down based on business complexity and expected evolution of the application: if core is expected to only ever be accessed through the web service, code from core handlers could be moved to HTTP handlers. On the other hand, if core is to be exposed through multiple of web, gRPC, console, or a long-running service, the extra indirection with core handlers becomes valuable.

The sample constraints itself to The Blue Book concepts rather than cutting corners due to unknown unknowns. That means implementing CQRS, aggregates, entities, domain events, and so on. For the HTTP API, the sample adheres to the Zalando API guidelines. It doesn't mean The Blue Book and the Zalando API guidelines are the end all, be all, but it's important the sample adopts constraints reflecting a larger real-world application.

Getting started

Running the tests or the web app creates the SQLite databases in the Git root as scrum_web.sqlite and scrum_test.sqlite.

$ dotnet tool restore
$ dotnet build
$ dotnet test
$ dotnet run --project src/Scrum

Opening the Git repository with VSCode will make it pick up the DevContainer configuration.

Operations

# Authentication (supported roles: member and/or admin)
## Post
curl "https://localhost:5000/authentication/issue-token?userId=1&roles=member,admin" --insecure --request POST
curl https://localhost:5000/authentication/renew-token --insecure --request POST -H "Authorization: Bearer <token>"
curl https://localhost:5000/authentication/introspect --insecure --request POST -H "Authorization: Bearer <token>"

# Stories
## Post
curl https://localhost:5000/stories --insecure --request POST -H 'Content-Type: application/json' -H 'Authorization: Bearer <token>' -d '{"title": "title", "description": "description"}'
curl https://localhost:5000/stories/<storyId>/tasks --insecure --request POST -H 'Content-Type: application/json' -H 'Authorization: Bearer <token>' -d '{"title": "title","description": "description"}'

## Put
curl https://localhost:5000/stories/<storyId> --insecure --request PUT -H 'Content-Type: application/json' -H 'Authorization: Bearer <token>' -d '{"title": "title1","description": "description1"}'
curl https://localhost:5000/stories/<storyId>/tasks/<taskId> --insecure --request PUT -H 'Content-Type: application/json' -H 'Authorization: Bearer <token>' -d '{"title": "title1","description": "description1"}'

## Delete
curl https://localhost:5000/stories/<storyId>/tasks/<taskId> --insecure --request DELETE -H 'Authorization: Bearer <token>'
curl https://localhost:5000/stories/<storyId> --insecure --request DELETE -H 'Authorization: Bearer <token>'

## Get
curl https://localhost:5000/stories/<storyId> --insecure -H 'Authorization: Bearer <token>'
curl "https://localhost:5000/stories?limit=<limit>&cursor=<cursor>" --insecure -H 'Authorization: Bearer <token>'

# PersistedDomainEvents
## Get
curl "https://localhost:5000/persisted-domain-events/<aggregateId>?limit=<limit>&cursor=<cursor>" --insecure -H 'Authorization: Bearer <token>'

# Health
## Get
curl https://localhost:5000/health --insecure

See also

• Implementing Domain-Driven Design by Vaughn Vernon (The Blue Book).
• Domain Modeling Made Functional: Tackle Software Complexity with Domain-Driven Design and F# by Scott Wlaschin.
• Jason Taylor's C# Clean Architecture Solution Template.
• Uncle Bob: Architecture the Lost Years.
• .NET Microservices: Architecture for Containerized .NET Applications, specifically the chapter on Tackling Business Complexity in a Microservice with DDD and CQRS Patterns.
• F# units of measure for primitive non-numeric types