Prisma Migrations in Production: Zero-Downtime Deployments With Expand-Contract

Prisma migrations can take your app down if done wrong. Running prisma migrate deploy on a live database while traffic is flowing is how you get a 3 AM incident.

Here's the zero-downtime migration strategy.

Why Migrations Break Production

The danger zone: your migration runs while old code is still serving requests.

Example:

1. You rename column user_name to username
2. Migration runs -- old column gone, new column exists
3. Old app instances still query user_name -- crash

Even a 2-second deploy window causes errors. At scale, deploys take minutes.

The Expand-Contract Pattern

The solution: never remove or rename in one step. Expand first, contract later.

Phase 1: Expand (backwards-compatible)

• Add new column alongside old one
• New code writes to both columns
• Old code still reads from old column -- no breakage

Phase 2: Migrate data

• Backfill new column from old column
• Verify all rows have new column populated

Phase 3: Contract (after all old instances are gone)

• New code reads from new column only
• Deploy and verify
• Drop old column in a separate migration

Step-By-Step: Renaming a Column

Goal: rename users.full_name to users.display_name

// Step 1: Add new column (keep old one)
model User {
  id           String  @id
  full_name    String  // Old column -- keep for now
  display_name String? // New column -- nullable initially
}

npx prisma migrate dev --name add_display_name

// Step 2: Update code to write to both
await db.user.update({
  where: { id },
  data: {
    full_name: name,      // Keep writing old column
    display_name: name    // Also write new column
  }
})

-- Step 3: Backfill existing rows
-- Run this as a one-off script, not in migration
UPDATE users SET display_name = full_name WHERE display_name IS NULL;

// Step 4: Make new column required (all rows populated)
model User {
  id           String @id
  full_name    String // Still here
  display_name String // Now required
}

// Step 5: Switch reads to new column
// Old: user.full_name
// New: user.display_name
// Deploy this version, verify, wait for old instances to drain

// Step 6: Drop old column (safe now)
model User {
  id           String @id
  display_name String
}

Additive Migrations Are Always Safe

These never cause downtime:

• Adding a nullable column
• Adding a table
• Adding an index (unless it locks the table -- use CONCURRENTLY)
• Adding a foreign key with DEFERRABLE INITIALLY DEFERRED

These require expand-contract:

• Renaming a column
• Changing a column type
• Making a nullable column required
• Dropping a column

Running Migrations Safely in CI/CD

# .github/workflows/deploy.yml
deploy:
  steps:
    - name: Run migrations
      run: npx prisma migrate deploy
      env:
        DATABASE_URL: ${{ secrets.MIGRATION_DATABASE_URL }}
      # Uses migration user with broader permissions

    - name: Deploy app
      run: vercel --prod
      # Migrations run BEFORE new code deploys
      # New code must handle both old and new schema

Checking Migration Status

# See which migrations have run
npx prisma migrate status

# In production, run via environment variable
DATABASE_URL=$PROD_DATABASE_URL npx prisma migrate status

Rollback Strategy

Prisma doesn't support automatic rollback (SQL DDL is hard to reverse). Your options:

1. Feature flags: Gate new code behind a flag, disable if migration fails
2. Blue-green deployment: Keep old environment running, switch traffic back
3. Manual rollback migration: Write a reverse migration by hand

-- Rollback: add the old column back if you dropped it
ALTER TABLE users ADD COLUMN full_name TEXT;
UPDATE users SET full_name = display_name;

Pre-Wired in the Starter

The AI SaaS Starter includes a migration workflow:

• Separate migration and app database users
• CI/CD that runs migrations before deploy
• db:migrate and db:status npm scripts
• Documentation for the expand-contract pattern

AI SaaS Starter Kit -- $99 one-time -- production database patterns included. Clone and ship.

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