Deploying to Vercel

FastAPI Interactions is designed for Vercel's serverless Python runtime. Each interaction is handled as a stateless HTTP request with no persistent connections or startup overhead.

Project structure

Vercel's Python runtime automatically detects a FastAPI instance named app at your entrypoint. Since bot.app exposes a FastAPI instance, you just need to export it.

my-bot/
├── main.py
├── commands.py
├── sync_commands.py
├── .env

See Vercel's FastAPI documentation for more details.

Environment variables

Your bot needs Discord credentials. Never hardcode these — use environment variables instead.

Local Development: Create a .env file and use environs to load it:

pip install environs

.env:

DISCORD_APP_ID=123
DISCORD_PUBLIC_KEY=456
DISCORD_BOT_TOKEN=567

Production (Vercel): Configure variables in the Vercel dashboard under Settings → Environment Variables. Scope DISCORD_BOT_TOKEN and DISCORD_PUBLIC_KEY to Production only so preview deployments don't affect your live bot.

Variable	Description
`DISCORD_APP_ID`	Your Discord application ID
`DISCORD_PUBLIC_KEY`	Ed25519 public key from the Developer Portal
`DISCORD_BOT_TOKEN`	Bot token, prefixed with `Bot`

Application setup

Entrypoint

Create main.py to initialize your bot and expose the FastAPI app:

# main.py
from fastapi_interactions import Bot
from .commands import router
from environs import env

env.read_env()

bot = Bot(
    app_id=env.int('DISCORD_APP_ID'),
    public_key=env.str(DISCORD_PUBLIC_KEY'),
    bot_token=env.star('DISCORD_BOT_TOKEN')
)

bot.attach_router(router)
app = bot.app

Warning

The variable must be named app and must be a FastAPI instance. Vercel's runtime detects it by name.

Commands

Define your commands in commands.py:

#commands.py
from fastapi_interactions.commands import CommandRouter, Option

router = CommandRouter('my-router')

@router.command(name='username', description='Retrieve your username')
async def username(ctx):
    return f'Hello {ctx.user.username}'

@router.command(name='echo', description='Echo a text')
@Option.string(name='text', description='Text to echo')
async def echo(ctx, text: str):
    return text

Syncing commands

Command syncing happens at deploy time, not at runtime. Create sync_commands.py:

# sync_commands.py
from fastapi_interactions import Bot
from .commands import router
from environs import env
import sys

env.read_env()

vercel_env = env.str('VERCEL_ENV')

if vercel_env != 'Production':
    print(f'Skipping command sync: VERCEL_ENV={vercel_env!r}')
    sys.exit(0)

bot = Bot(
    app_id=env.int('DISCORD_APP_ID'),
    public_key=env.str(DISCORD_PUBLIC_KEY'),
    bot_token=env.star('DISCORD_BOT_TOKEN')
)

bot.attach_router(router)
bot.sync_commands()

This script skips syncing on preview builds, preventing them from overwriting your live commands.

Configure build command

In the Vercel dashboard under Settings → Build & Development Settings, set the build command to:

python sync_commands.py

Commands are synced automatically on every production deploy. Global command registration can take up to an hour to propagate. During development, use guild-scoped routers for instant updates:

router = CommandRouter(guild_id="123456789")

After deployment

Once your app is live, set your Discord interactions endpoint URL in the Developer Portal:

https://your-project.vercel.app/interactions

Discord will verify the endpoint by sending a PING handshake. Once confirmed, your bot is ready.

Performance

Vercel's serverless functions spin up on demand. Discord requires a response within 3 seconds. The framework adds minimal overhead — no database connections, no gateway handshakes — so cold starts are typically well within that window.

Warning

Long-running operations don't work with deferred responses on serverless because the container terminates after the HTTP response is sent. If a command needs more than 3 seconds, either complete the work within the response window, or deploy to traditional hosting. Most Discord bots don't need this pattern.