> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fly.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Databases

Most web servers store data in a database, and there are many databases to chose from.
Examples include running [PostgreSQL](/postgres) on fly.io's infrastructure,
embedding [SQLite](https://www.sqlite.org/index.html) in your application, or accessing
a [MongoDB](https://www.mongodb.com/) database hosted elsewhere.

For maximum flexibility, it generally is best if your application doesn't hard code the
path to the database, but rather extracts the path from the environment.  We recommend,
and will by default automatically set, `DATABASE_URL` to this path when we either provide
or can detect the database.

For cases where an external database is used, you can set this yourself using
[`fly secrets set`](/apps/secrets#set-secrets).

## Accessing the DATABASE\_URL value

The way you access the `DATABASE_URL` value depends on the module or ORM you are using.

For Prisma, ensure your `prisma/schema.prisma` file contains:

```js theme={null}
const url = env("DATABASE_URL")
```

For drizzle/sqlite3:

```js theme={null}
const db = drizzle(new Database(new URL(process.env.DATABASE_URL).pathname));
```

For drizzle/postgres:

```js theme={null}
const pool = new Pool({ connectionString: process.env.DATABASE_URL });
const db = drizzle(pool)
```

For knex/sqlite3:

```js theme={null}
  client: 'sqlite3',
  connection: { filename: new URL(process.env.DATABASE_URL).pathname },
```

For knex/pg:

```js theme={null}
  client: 'pg',
  connection: process.env.DATABASE_URL
```

for sqlite3:

```js theme={null}
const db = new sqlite3.Database(new URL(process.env.DATABASE_URL).pathname);
```

for postgres:

```js theme={null}
const client = new pg.Client({connectionString: process.env.DATABASE_URL});
```

for mongodb:

```js theme={null}
const client = new mongodb.MongoClient(process.env.DATABASE_URL);
```

<h2 id="ssl-tls">
  SSL/TLS
</h2>

If your database is hosted external to fly.io, you generally will want to connect to
it securely.  The way to do so varies by database and adapter.  An example for
postgres can be found at [node-postgres features > ssl](https://node-postgres.com/features/ssl).

Equally important, if your database is hosted within the
[Fly.io private network](/networking/private-networking), you will *not*
want to connect with SSL/TLS connection options.

## Migrations

In order to use a database we need to load and evolve a schema.  This often
involves running a tool like Prisma's [migrate](https://www.prisma.io/docs/concepts/components/prisma-migrate) tool.

For databases other than Sqlite3, this is best done as a one-off command run in a temporary VM.  This can be accomplished by adding a
[`release_command`](/reference/configuration#run-one-off-commands-before-releasing-a-deployment) in your `fly.toml` file.

For sqlite3, a different approach is required as the migration will need to be run on each machine that has a volume mounted.  This can be accomplished by creating a small script that first runs the migrate command then run the web server start script.  You can place this script in your source tree, and then use the following command to replace the CMD in the Dockerfile:

```bash theme={null}
npx @flydotio/dockerfile --cmd=file
```