Deploy a flask app with Vercel

How to setup Vercel CLI (MacOS)

node -v
npm -v

brew install node

npm install -g vercel

# verify
vercel --version

How to setup Vercel CLI (Ubuntu)

How to setup Vercel CLI (Windows)

vercel login

Flask app

create a folder named “api”
create “requirements.txt” file and “vercel.json” file
create “app.py” and templates folder
templates => html files( for example, index.html)

use the following template for vercel.json file:

  {
  "rewrites": [
    { 
        "source": "/(.*)", "destination": "/api/app.py" 
    }
    
      ] 
  }

Git push

Run your flask app in local system
Git push your project

https://vercel.com

Create an account in vercel and login to the page
Continue with Github and allow github authentication.
Select only specfic repositories and import
Set a Domain name and click Deploy
The deploy logs will be displayed and any error while deployment will be shown.

Congratulations! You have Deployed your flask app.

Vercel Deployment Guide for KBot

Complete guide for deploying and debugging KBot on Vercel.

Prerequisites

Vercel account (sign up at https://vercel.com)
Vercel CLI installed: npm i -g vercel
Git repository with your KBot code

Initial Deployment

Option 1: Deploy via Vercel Dashboard (Easiest)

Go to https://vercel.com/dashboard
Click “Add New…“ → “Project”
Import your Git repository (GitHub, GitLab, or Bitbucket)
Configure project:
- Framework Preset: Other
- Build Command: Leave empty (or pip install -r requirements.txt)
- Output Directory: Leave empty
- Install Command: pip install -r requirements.txt
Add Environment Variables:
- SLACK_BOT_TOKEN = xoxb-your-bot-token
- SLACK_SIGNING_SECRET = your-signing-secret
Click “Deploy”

Option 2: Deploy via CLI

# Login to Vercel
vercel login

# Deploy to production
vercel --prod

# Follow the prompts to link your project

Environment Variables

Add Environment Variables

Via Dashboard:

Go to https://vercel.com/dashboard
Select your slack-kbot project
Go to Settings → Environment Variables
Click “Add New”
Add each variable:
- Key: SLACK_BOT_TOKEN
- Value: xoxb-your-actual-token
- Environment: Production, Preview, Development (select all)
Repeat for SLACK_SIGNING_SECRET

Via CLI:

# Add environment variable
vercel env add SLACK_BOT_TOKEN production
# Paste your token when prompted

vercel env add SLACK_SIGNING_SECRET production
# Paste your secret when prompted

Update Environment Variables

If you need to update a token (e.g., after adding new Slack scopes):

Via Dashboard:

Go to Settings → Environment Variables
Find the variable (e.g., SLACK_BOT_TOKEN)
Click “Edit” (pencil icon)
Update the value
Click “Save”
Important: Redeploy your app for changes to take effect

Via CLI:

# Remove old variable
vercel env rm SLACK_BOT_TOKEN production

# Add new variable
vercel env add SLACK_BOT_TOKEN production

After Updating Environment Variables

⚠️ You must redeploy for changes to take effect!

Via Dashboard:

Go to Deployments tab
Click the three dots (…) on the latest deployment
Click “Redeploy”
Confirm the redeployment

Via CLI:

vercel --prod

Viewing Logs

Via Dashboard (Recommended)

Go to https://vercel.com/dashboard
Click on your slack-kbot project
Click Deployments tab
Click on the latest deployment
Click Functions tab
View real-time logs with filters:
- Filter by status (200, 404, 500, etc.)
- Filter by time range
- Search for specific text

Via CLI

View logs for a specific deployment:

# Get deployment URL first
vercel ls

# View logs (replace with your actual URL)
vercel logs https://slack-kbot.vercel.app

# Or use deployment ID
vercel logs dpl_xxxxxxxxxxxxx

View logs as JSON (for parsing with jq):

vercel logs https://slack-kbot.vercel.app --json

# Filter for errors only
vercel logs https://slack-kbot.vercel.app --json | jq 'select(.statusCode >= 400)'

# Filter for Slack API errors
vercel logs https://slack-kbot.vercel.app --json | jq 'select(.message | contains("Slack API error"))'

Common CLI commands:

# List all deployments
vercel ls

# List deployments for specific project
vercel ls slack-kbot

# Get deployment details
vercel inspect https://slack-kbot.vercel.app

# View project info
vercel project ls

Testing Your Deployment

Test Endpoints

# Test root endpoint (should return unique ID)
curl https://slack-kbot.vercel.app/
# Expected: {"unique_id":"7262-20260128"}

# Test health endpoint
curl https://slack-kbot.vercel.app/health
# Expected: {"status":"healthy","bot":"KBot"}

# Test Slack events endpoint (will fail without proper signature)
curl -X POST https://slack-kbot.vercel.app/slack/events
# Expected: 401 Unauthorized (this is correct - signature required)

Check Deployment Status

# Via CLI
vercel ls

# Via browser
# Go to: https://slack-kbot.vercel.app/health

Common Issues and Debugging

Issue 1: “Slack API error: missing_scope”

Symptoms:

Bot receives messages but doesn’t respond
Logs show: Slack API error: missing_scope

Cause:

The SLACK_BOT_TOKEN in Vercel is outdated
You added new scopes in Slack but didn’t update the token in Vercel

Fix:

Go to Slack API → OAuth & Permissions
Copy the current Bot User OAuth Token
Update SLACK_BOT_TOKEN in Vercel (Settings → Environment Variables)
Redeploy the app

Issue 2: “invalid_auth” or “not_authed”

Symptoms:

Logs show: Slack API error: invalid_auth

Cause:

Wrong token in Vercel
Using App-Level Token (xoxe-) instead of Bot Token (xoxb-)

Fix:

Verify you’re using Bot User OAuth Token (starts with xoxb-)
Update SLACK_BOT_TOKEN in Vercel
Redeploy

Issue 3: Bot doesn’t receive events

Symptoms:

No logs appear when you message the bot
/slack/events endpoint not being called

Cause:

Event Subscriptions URL not configured in Slack
URL not verified (no green checkmark)

Fix:

Go to Slack API → Event Subscriptions
Set Request URL to: https://slack-kbot.vercel.app/slack/events
Wait for green checkmark ✅ “Verified”
Make sure bot events are added (message.im, etc.)
Reinstall app to workspace

Issue 4: “Invalid signature” errors

Symptoms:

Logs show: Invalid request signature
401 Unauthorized responses

Cause:

Wrong SLACK_SIGNING_SECRET in Vercel
Extra spaces in environment variable

Fix:

Go to Slack API → Basic Information → App Credentials
Copy Signing Secret (click “Show”)
Update SLACK_SIGNING_SECRET in Vercel (no extra spaces!)
Redeploy

Issue 5: Deployment fails

Symptoms:

Build fails
“Error: No Python version specified”

Fix: Create runtime.txt in your project root:

python-3.11

Or create vercel.json:

{
  "builds": [
    {
      "src": "app.py",
      "use": "@vercel/python"
    }
  ],
  "routes": [
    {
      "src": "/(.*)",
      "dest": "app.py"
    }
  ]
}

Issue 6: Can’t find deployment with CLI

Symptoms:

vercel logs slack-kbot fails
Error: “Can’t find the deployment”

Fix:

# Link to the project first
vercel link

# Or use the full URL
vercel logs https://slack-kbot.vercel.app

# Or list deployments first
vercel ls

Monitoring

Real-time Monitoring

Via Dashboard:

Go to your project → Deployments
Click latest deployment → Functions
Logs update in real-time
Use filters to find specific issues

Via CLI:

# Follow logs in real-time
vercel logs https://slack-kbot.vercel.app --follow

Check for Errors

In Dashboard:

Look for red status codes (400, 500, etc.)
Filter by “Error” level
Check “Messages” column for error details

Via CLI:

# Get logs as JSON and filter for errors
vercel logs https://slack-kbot.vercel.app --json | jq 'select(.statusCode >= 400)'

Common Log Messages

Message	Meaning	Action
`URL verification challenge received`	Slack verifying your endpoint	✅ Normal
`Message sent to channel`	Bot successfully replied	✅ Normal
`Invalid request signature`	Wrong signing secret	Update `SLACK_SIGNING_SECRET`
`Slack API error: missing_scope`	Token missing permissions	Update `SLACK_BOT_TOKEN`
`Slack API error: invalid_auth`	Wrong or expired token	Update `SLACK_BOT_TOKEN`
`Duplicate event ignored`	Event deduplication working	✅ Normal

Redeployment

When to Redeploy

Redeploy after:

Updating environment variables
Changing code
Adding new dependencies to requirements.txt
Updating Slack scopes (after updating token in Vercel)

How to Redeploy

Via Dashboard:

Go to Deployments tab
Click three dots on latest deployment
Click “Redeploy”
Confirm

Via CLI:

# Redeploy current code
vercel --prod

# Force redeploy without changes
vercel --prod --force

Via Git:

# Push to your main branch
git push origin main

# Vercel auto-deploys on push (if connected to Git)

Rollback

If a deployment breaks something:

Via Dashboard:

Go to Deployments tab
Find a working deployment
Click three dots → “Promote to Production”

Via CLI:

# List deployments
vercel ls

# Promote a specific deployment
vercel promote <deployment-url>

Custom Domain (Optional)

Add Custom Domain

Go to Settings → Domains
Click “Add”
Enter your domain (e.g., kbot.yourdomain.com)
Follow DNS configuration instructions
Update Slack Event Subscriptions URL to your custom domain

Performance Tips

Use Production Environment: Always deploy with --prod flag
Monitor Cold Starts: Serverless functions may have cold starts
Keep Dependencies Minimal: Only include required packages
Use Logging: Add strategic log points for debugging
Set Timeouts: Vercel has 10s timeout for Hobby plan, 60s for Pro

Security Best Practices

Never commit tokens: Keep .env in .gitignore
Use Environment Variables: Store all secrets in Vercel
Verify Signatures: Always validate Slack signatures (already implemented)
Rotate Tokens: Periodically rotate your Slack tokens
Monitor Logs: Check for suspicious activity

Useful Links

Support

If you encounter issues:

Check Vercel logs (Dashboard or CLI)
Verify environment variables are set correctly
Test endpoints with curl
Check Slack API dashboard for errors
Review Vercel status: https://www.vercel-status.com/

Quick Reference

# Deploy
vercel --prod

# View logs
vercel logs https://slack-kbot.vercel.app

# List deployments
vercel ls

# Add environment variable
vercel env add VARIABLE_NAME production

# Remove environment variable
vercel env rm VARIABLE_NAME production

# Link project
vercel link

# Inspect deployment
vercel inspect https://slack-kbot.vercel.app

# Promote deployment to production
vercel promote <deployment-url>

Vercel CLI

vercel login

vercel link
Vercel CLI 48.2.9
? Set up “~/kact/slack-kbot”? yes
? Which scope should contain your project? TactEditor's projects
? Found project “tacteditors-projects/slack-kbot”. Link to it? yes
✅  Linked to tacteditors-projects/slack-kbot (created .vercel)


vercel ls

Vercel CLI 48.2.9
> Deployments for tacteditors-projects/slack-kbot [165ms]

  Age     Deployment                                                       Status      Environment     Duration     Username
  3m      https://slack-kbot-qpvvd0z1l-tacteditors-projects.vercel.app     ● Ready     Production      24s          tacteditor
  6m      https://slack-kbot-1cvohw9m6-tacteditors-projects.vercel.app     ● Ready     Production      13s          tacteditor

vercel logs <deployment-url>

vercel logs https://slack-kbot.vercel.app

vercel --prod

vercel env rm UNIQUE_COUNTRY production
printf "india" | vercel env add UNIQUE_COUNTRY production

vercel --prod

vercel --prod --force

vercel switch vipranan

vercel whoami
vercel teams ls

vercel logs

# Re-link to your personal account or correct team
vercel link

Deploy a flask app with Vercel

How to setup Vercel CLI (MacOS)

How to setup Vercel CLI (Ubuntu)

How to setup Vercel CLI (Windows)

How login on vercel?

Flask app

Git push

Login to vercel

Congratulations! You have Deployed your flask app.

Vercel Deployment Guide for KBot

Prerequisites

Initial Deployment

Option 1: Deploy via Vercel Dashboard (Easiest)

Option 2: Deploy via CLI

Environment Variables

Add Environment Variables

Update Environment Variables

After Updating Environment Variables

Viewing Logs

Via Dashboard (Recommended)

Via CLI

Testing Your Deployment

Test Endpoints

Check Deployment Status

Common Issues and Debugging

Issue 1: “Slack API error: missing_scope”

Issue 2: “invalid_auth” or “not_authed”

Issue 3: Bot doesn’t receive events

Issue 4: “Invalid signature” errors

Issue 5: Deployment fails

Issue 6: Can’t find deployment with CLI

Monitoring

Real-time Monitoring

Check for Errors

Common Log Messages

Redeployment

When to Redeploy

How to Redeploy

Rollback

Custom Domain (Optional)

Add Custom Domain

Performance Tips

Security Best Practices

Useful Links

Support

Quick Reference

Vercel CLI