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Hosting overview

You have written a command and a read model, and now something has to listen on a port. Maybe your team already runs Express, or you want nothing between Arc and Node’s own HTTP server. Arc for TypeScript keeps those decisions apart: the core owns the application model, and the host only delivers requests to it. Your commands, queries, validators, and services do not change when you change host.

Choose the host

Section titled “Choose the host”
HostPackage and entry pointUse it when
Standalone Node host@cratis/arc.core: app.run() or app.start()You want Arc routes, and optionally a built frontend, on one port with no web framework
Your own Node server@cratis/arc.core: createArcNodeHandler(server)You already own a node:http or node:https server and want Arc as its request handler
Express 5@cratis/arc.express: app.use(cratisArc(arcApp))Your application already uses Express middleware and routes
Fastify 5@cratis/arc.fastify: app.register(cratisArc, { arc: arcApp })Your application already uses Fastify plugins and hooks
Hono 4@cratis/arc.hono: app.use(cratisArc(arcApp))Your application already uses Hono, on Node through @hono/node-server
Any Fetch API host or none@cratis/arc.core: server.handle(request)You call Arc from a spec, a job, or a runtime that speaks Request and Response
app.run / app.start
cratisArc adapters
app.server.handle
ArcApplication.createBuilder()

add, discover, services
ArcApplication

app.server: ArcServer
Standalone Node host
Your web framework
Fetch API Request

Every host runs the same pipeline: authentication, tenant resolution, authorization, validation, then your code. A difference between hosts is either a limit of the host framework, documented on its page, or a bug.

What the host owns and what it does not

Section titled “What the host owns and what it does not”

The host owns the listener, TLS, and shutdown order. Arc owns routes, body parsing, the result envelope, status codes, correlation, and cancellation of context.signal when a client disconnects. Adapters hand Arc the raw body, so an adapter must be mounted before any body parser that would consume it. Host adapters lists what each adapter does with paths and bodies.

Observable queries add one more concern: WebSocket upgrades. The standalone host handles them itself; each framework adapter has a separate mount call because Express, Fastify, and Hono accept upgrades differently. See WebSockets.

Then choose storage and client output

Section titled “Then choose storage and client output”

Arc does not require a database or an event store. A command can call your own service, write to storage through an optional integration, or return a response. Add what the application needs:

  • MongoDB for tenant-scoped collections with change-stream observation.
  • SQL with Drizzle for tenant-scoped SQLite and PostgreSQL reads.
  • Chronicle, experimental, when commands should append events.

Proxy generation is a separate build step. It reads your TypeScript source and writes typed clients for the published @cratis/arc frontend runtime; it never queries a running server.

Continue

Section titled “Continue”