Question 1

What is SvelteKit and what is it used for?

Accepted Answer

SvelteKit is an app framework, sometimes called a metaframework, built on top of Svelte for rapidly developing robust, performant web applications. It solves the tricky problems of building something production-ready, such as routing, server-side rendering, and static site generation. Think of Svelte as the component layer and SvelteKit as the full application layer on top of it. SvelteKit apps run on Fly.io as plain Node servers via the @sveltejs/adapter-node build output.

Question 2

How do I deploy a SvelteKit app to Fly.io?

Accepted Answer

Install the Node adapter (npm i -D @sveltejs/adapter-node), install flyctl, and run fly launch from your project. The launcher detects SvelteKit, drops in @flydotio/dockerfile, generates a fly.toml, and offers to attach Postgres or Redis. After the wizard, push subsequent changes with fly deploy.

Question 3

Why does SvelteKit need the Node adapter specifically?

Accepted Answer

SvelteKit needs an adapter that produces a runnable server binary, and on Fly.io that's @sveltejs/adapter-node. The default auto adapter only emits platform-specific output, so fly launch can't run the build directly. Switching to the Node adapter takes one line in svelte.config.js.

Question 4

How do I add a database to my SvelteKit app on Fly.io?

Accepted Answer

Managed Postgres is the supported path on Fly.io. Run fly launch --db mpg and the launcher provisions a Managed Postgres cluster and attaches it in the same run, or add one to an existing app with fly mpg create and fly mpg attach -a . Attaching writes DATABASE_URL onto the app as a secret; read it through $env/dynamic/private, which resolves at runtime, so your ORM of choice connects with no extra wiring. Fly.io handles automatic backups and recovery, high availability with automatic failover, performance monitoring, resource scaling, and encryption of data at rest and in transit.

Question 5

Can I use SQLite with SvelteKit on Fly.io?

Accepted Answer

Yes. SQLite runs on a persistent Fly volume mounted to one Machine, which is the simplest option for read-heavy apps. SQLite on a volume is single-writer, so one Machine owns the database file.

Question 6

Why is my SvelteKit build failing with "Cannot find package 'svelte'"?

Accepted Answer

SvelteKit is a compiler, so its build dependencies typically belong in devDependencies. When the Fly.io build runs npm ci --omit=dev inside the generated Dockerfile, those packages get pruned and the runtime crashes looking for them. Move build-required packages into dependencies, or update the Dockerfile to install dev dependencies before the build step and prune afterwards.

Question 7

How do I set environment variables for a SvelteKit app on Fly.io?

Accepted Answer

Use fly secrets set KEY=value for anything sensitive like API keys or database URLs. Secrets are encrypted and injected into the Machine's environment at boot, and SvelteKit exposes them through $env/static/private and $env/dynamic/private. For non-sensitive build-time values, the [env] block in fly.toml works too.

Question 8

Can I deploy a SvelteKit app that uses Bun instead of Node?

Accepted Answer

Yes. On Fly.io, the bun-sveltekit adapter produces a Bun-compatible server, and fly launch will run it inside a Bun-based Dockerfile if you've already configured the adapter. Bun also sidesteps a class of CJS/ESM compatibility issues that can trip up the Node adapter, so it's worth trying if your build keeps breaking on module resolution.

Question 9

Does Fly.io support SvelteKit with TypeScript or only JavaScript?

Accepted Answer

Yes, TypeScript works the same as JavaScript. fly launch reads your package.json and builds whatever the Node adapter emits, including the compiled output from a TypeScript project. There's no Fly-specific configuration needed beyond what the SvelteKit template ships with.

Question 10

Is Fly.io overkill for a simple SvelteKit app?

Accepted Answer

No. A standard SvelteKit app with a Postgres database in one region is the ordinary case Fly.io is built for. fly launch reads your code, writes the Dockerfile and the fly.toml, and deploys, and fly launch --db mpg provisions Managed Postgres and attaches it in the same run. Fly.io sits between a traditional PaaS and a hyperscaler, so the short path is the default and the deeper controls are there for when you actually want them.

Question 11

Does deploying a SvelteKit app on Fly.io require a lot of infrastructure decisions?

Accepted Answer

No. On the standard path you make one decision, which is whether to accept the settings fly launch proposes. Fly.io proposes a region and a Machine size, generates the Dockerfile, detects the port your app listens on, turns on HTTPS, assigns a hostname, writes the release_command that runs your migrations, and sets DATABASE_URL as a secret when Managed Postgres is attached. Each of those is a line in fly.toml you can change later, and none of them is a line you have to write first.

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