How to Dockerize SvelteKit

This guide shows you how to containerize your SvelteKit application for simplified deployment and management. Remember: this is for SvelteKit, not Svelte!

Setting Up

If you lack a SvelteKit project, create one:

npx sv create my-svelte-app --template demo --types ts

Next, configure SvelteKit to use the adapter-node for Node.js compatibility, essential for containerization. Install it:

npm i -D @sveltejs/adapter-node

Modify svelte.config.js:

// svelte.config.js
- import adapter from '@sveltejs/adapter-auto';
+ import adapter from '@sveltejs/adapter-node';

Now, create your Dockerfile. This instructs Docker on building and running your application:

# Builder stage
FROM node:22-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build
RUN npm prune --production

# Final stage
FROM node:22-alpine
WORKDIR /app
COPY --from=builder /app/build build/
COPY --from=builder /app/node_modules node_modules/
COPY package.json .
EXPOSE 3000
ENV NODE_ENV=production
CMD [ "node", "build" ]

This Dockerfile uses a multi-stage build. The builder stage compiles your app, and the final stage creates a leaner runtime image.

To streamline the build process, create a .dockerignore file:

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

Generally, install all dependencies as devDependencies (using npm i -D <package></package>). This lets SvelteKit bundle them, removing unused imports. However, if you encounter issues like __dirname undefined during the build, install the package as a regular dependency. If all dependencies are devDependencies, you can omit copying node_modules in the final Docker stage, further minimizing image size.

Build your Docker image:

docker build -t my-sveltekit-app .

Run the containerized app:

docker run -p 3000:3000 my-sveltekit-app

Access your app at http://localhost:3000.

Environment Variables

SvelteKit offers four ways to manage environment variables: $env/dynamic/private, $env/dynamic/public, $env/static/private, and $env/static/public. Remember that different deployment platforms handle these differently; consult their documentation.

For form actions and server-side features, correctly set the ORIGIN environment variable to prevent cross-site POST errors:

docker run -p 3000:3000 -e ORIGIN=http://localhost:3000 my-sveltekit-app

Replace http://localhost:3000 with your production domain.

Production Optimization

1. Health Checks: Add a /health endpoint and use Docker's HEALTHCHECK instruction:

HEALTHCHECK --interval=30s --timeout=3s \
  CMD wget --no-verbose --tries=1 --spider http://localhost:3000/health || exit 1

2. Memory Limits: Set Node.js memory limits:

docker run -p 3000:3000 -e NODE_OPTIONS="--max-old-space-size=512" my-sveltekit-app

3. Security Scanning: Regularly scan for vulnerabilities:

docker scout quickview

Conclusion

You've now containerized your SvelteKit application. For deployment, consider sliplane.io.

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