# Backends on Vercel

Backends deployed to Vercel receive the benefits of Vercel's infrastructure, including:

- [Fluid compute](/content/docs/fluid-compute/index.html): Zero-configuration, optimized concurrency, dynamic scaling, background processing, automatic cold-start prevention, region failover, and more
- [Active CPU pricing](/content/docs/functions/usage-and-pricing/index.html): Only pay for the CPU you use, not waiting for I/O (e.g. calling AI models, database queries)
- [Instant Rollback](/content/docs/instant-rollback/index.html): Quickly revert to a previous production deployment
- [Vercel Firewall](/content/docs/vercel-firewall/index.html): A robust, multi-layered security system designed to protect your applications
- [Preview deployments with Deployment Protection](/content/docs/deployments/environments#preview-environment-pre-production/index.html): Secure your preview environments and test changes safely before production
- [Rolling releases](/content/docs/rolling-releases/index.html): Gradually roll out backends to detect errors early

## [Zero-configuration backends](/content/docs/frameworks/backend#zero-configuration-backends/index.html)

Deploy the following backends to Vercel with zero-configuration.

### Elysia

Ergonomic framework for humans

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/elysia/index.html)

### Express

Fast, unopinionated, minimalist web framework for Node.js

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/express/index.html) [View Demo](https://express-vercel-example-demo.vercel.app/)

### FastAPI

FastAPI framework, high performance, easy to learn, fast to code, ready for production

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/fastapi/index.html) [View Demo](https://vercel-fastapi-gamma-smoky.vercel.app/)

### Fastify

Fast and low overhead web framework, for Node.js

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/fastify/index.html)

### Flask

The Python micro web framework

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/flask/index.html)

### H3

Universal, Tiny, and Fast Servers

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/h3/index.html)

### Hono

Web framework built on Web Standards

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/hono/index.html) [View Demo](https://hono.vercel.dev/)

### Koa

Expressive middleware for Node.js using ES2017 async functions

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/koa/index.html)

### NestJS

Framework for building efficient, scalable Node.js server-side applications

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/nestjs/index.html)

### Nitro

Nitro is a next generation server toolkit.

[Deploy](/content/new/clone?repository-url=https://github.com/vercel/vercel/tree/main/examples/nitro/index.html) [View Demo](https://nitro-template.vercel.app/)

To process background tasks with Python, you can deploy [Celery](/content/docs/frameworks/backend/celery/index.html) or [Dramatiq](/content/docs/frameworks/backend/dramatiq/index.html) workers as queue-triggered Vercel Functions.

## [Adapting to Serverless and Fluid compute](/content/docs/frameworks/backend#adapting-to-serverless-and-fluid-compute/index.html)

If you are transitioning from a fully managed server or containerized environment to Vercel’s serverless architecture, you may need to rethink a few concepts in your application since there is no longer a server always running in the background.

The following are generally applicable to serverless, and therefore Vercel Functions (running with or without Fluid compute).

### [WebSockets](/content/docs/frameworks/backend#websockets/index.html)

Vercel Functions can serve WebSocket connections when [Fluid compute](/content/docs/fluid-compute/index.html) is enabled. WebSocket connections follow [Vercel Function limits](/content/docs/functions/limitations/index.html), including maximum duration, so clients should handle reconnects when a connection closes.

Store persistent state, rooms, presence, and pub/sub coordination in an external data store instead of relying on in-memory state. Learn more in the [WebSockets documentation](/content/docs/functions/websockets/index.html).

### [Database Connections](/content/docs/frameworks/backend#database-connections/index.html)

To manage database connections efficiently, [use the `attachDatabasePool` function from `@vercel/functions`](/content/docs/functions/functions-api-reference/vercel-functions-package#database-connection-pool-management/index.html).