Deploying a SvelteKit app with Docker on Fly.io

September 22nd, 2024

I often deploy SvelteKit apps with Docker, on platforms such as Fly.io, but I always forget the process. Here are some notes.

Use node adapter

Install it with npm:

npm install @sveltejs/adapter-node

Add it to svelte.config.js:

import adapter from "@sveltejs/adapter-node";

export default {
  kit: {
    adapter: adapter(),
  },
};

Add Dockerfile and .dockerignore

FROM node:lts-slim AS builder
WORKDIR /app
COPY package*.json .
RUN npm ci
COPY . .
RUN npm run build
RUN npm prune --production

FROM node:lts-slim
WORKDIR /app
COPY --from=builder /app/build build/
COPY --from=builder /app/node_modules node_modules/
COPY package.json .
EXPOSE 3000
CMD [ "node", "build" ]

Dockerfile
.dockerignore
.git
.gitignore
.gitattributes
README.md
.npmrc
.prettierrc
.eslintrc.cjs
.graphqlrc
.editorconfig
.svelte-kit
.vscode
node_modules
build
package
**/.env

Use dynamic environment variables instead of static

Change occurrences of:

import { API_KEY } from '$env/static/private';

to

import { env } from '$env/dynamic/private';

Access the environment variable with env.API_KEY

Then, add all environment variables to Fly.io secrets manager via the web console.

Update body size limit (if needed)

By default, SvelteKit has a small body size limit of 512KB. If the app requires large uploads, update the body size limit by setting BODY_SIZE_LIMIT as an environment variable via Fly.io console.