> ## 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.

# Connect Your Client

This guide covers how to connect your application to Fly Managed Postgres and configure your database client for reliable, performant connections.

## Quick start

After [creating your MPG cluster](/postgres/create-and-connect) and attaching your app, these are the essentials:

**1. Your connection string.** When you attach an app with `fly mpg attach`, Fly sets a `DATABASE_URL` secret on your app automatically. You can customize the variable name during attachment. Your app receives this as an environment variable at runtime. Both pooled and direct URLs are available from the **Connect** tab in your cluster's dashboard.

* **Pooled URL** (default): `postgresql://fly-user:YOUR_PASSWORD@pgbouncer.YOUR_CLUSTER.flympg.net/fly-db` — routes through PgBouncer. Use this for your application.
* **Direct URL**: `postgresql://fly-user:YOUR_PASSWORD@direct.YOUR_CLUSTER.flympg.net/fly-db` — bypasses PgBouncer. Use this for migrations, advisory locks, or `LISTEN/NOTIFY`.

SSL is enabled by default on all MPG connections. You do not need to set `sslmode` in your connection string.

**2. Set connection lifetime and idle timeout in your code.** These are settings you configure in your application's database client or connection pool library — not on the database or cluster side. Not all client libraries support these settings directly — see the [language-specific examples](#language-specific-configuration) below.

| Setting                 | Recommended value        | Why                                                        |
| ----------------------- | ------------------------ | ---------------------------------------------------------- |
| Max connection lifetime | **600 seconds** (10 min) | Recycle connections before the proxy closes them           |
| Idle connection timeout | **300 seconds** (5 min)  | Releases unused connections before they're forcibly closed |

**3. Set up a direct URL for migrations.** Most frameworks run migrations on deploy. Migrations use advisory locks and other session-scoped features that require the direct URL, not the pooled one.

```bash theme={null}
fly secrets set \
  DATABASE_URL="postgresql://...@pgbouncer.YOUR_CLUSTER.flympg.net/fly-db" \
  DIRECT_DATABASE_URL="postgresql://...@direct.YOUR_CLUSTER.flympg.net/fly-db"
```

```toml theme={null}
# fly.toml
[deploy]
  release_command = "/bin/sh -lc 'DATABASE_URL=$DIRECT_DATABASE_URL bin/migrate'"
```

See the [Phoenix guide](/postgres/guides-examples/phoenix-guide) for Elixir-specific migration setup.

**4. Disable prepared statements in transaction mode.** If your PgBouncer pool mode is set to **Transaction** (required for Ecto; recommended for high-throughput apps), you must disable named prepared statements in your client. PgBouncer can't track prepared statements across transactions. See [Cluster Configuration](/postgres/cluster-configuration) for how to change your pool mode.

***

## Why client configuration matters

Your Fly.io apps, as well as your Fly.io Postgres databases, sit behind Fly.io's proxy. Public and private traffic route through this proxy. Sometimes our proxy restarts and the proxy does its best to drain connections before restarting. Postgres doesn't have a protocol level mechanism to tell clients to stop sending queries on a particular connection, so we have to rely on client-side configuration to handle graceful handoff.

The proxy's shutdown timeout is **10 minutes**. Any connection that remains open after that is terminated. If your application holds connections for longer than this — which is the default behavior of most connection pools — you might run into errors like `tcp recv (idle): closed` or `ECONNRESET` during proxy deployments.

The fix is straightforward: configure your connection pool to **proactively recycle connections** on a shorter interval than the proxy's timeout.

## PgBouncer mode and your client

All MPG clusters include PgBouncer for connection pooling. The pool mode you choose on the cluster side affects what your client can do. See [Cluster Configuration](/postgres/cluster-configuration) for how to change modes.

**Session mode** (default): A PgBouncer connection is held for the entire client session. Full PostgreSQL feature compatibility — prepared statements, advisory locks, `LISTEN/NOTIFY`, and multi-statement transactions all work normally. Lower connection reuse.

**Transaction mode**: PgBouncer assigns a connection per transaction and returns it to the pool afterward. Higher throughput and connection reuse, but:

* **Named prepared statements** don't work — you must use unnamed/extended query protocol
* **Advisory locks** are not session-scoped — use the direct URL for migrations
* **`LISTEN/NOTIFY`** doesn't work — use an alternative notifier (see the [Phoenix guide](/postgres/guides-examples/phoenix-guide) for Oban examples)
* **`SET` commands** affect only the current transaction

If your ORM or driver supports it, transaction mode with unnamed prepared statements is the better choice for most web applications.

## Language-specific configuration

<AccordionGroup>
  <Accordion title="Node.js — pg (node-postgres)">
    ```javascript theme={null}
    const { Pool } = require('pg');

    const pool = new Pool({
      connectionString: process.env.DATABASE_URL,

      // Pool sizing
      max: 10,

      // Connection lifecycle
      idleTimeoutMillis: 300_000,       // 5 min — close idle connections
      maxLifetimeSeconds: 600,          // 10 min — recycle before proxy timeout
      connectionTimeoutMillis: 5_000,   // 5s — fail fast on connection attempts
    });
    ```

    `maxLifetimeSeconds` was added in `pg-pool` 3.5.1 (included with `pg` 8.8+). If you're on an older version, upgrade — this setting is critical for reliable connections on Fly.
  </Accordion>

  <Accordion title="Node.js — Prisma">
    Add the following query parameters to your connection string:

    | Parameter          | Value  | Purpose                                                  |
    | ------------------ | ------ | -------------------------------------------------------- |
    | `pgbouncer`        | `true` | Disables prepared statements for PgBouncer compatibility |
    | `connection_limit` | `10`   | Pool size per Prisma client instance                     |
    | `pool_timeout`     | `30`   | Seconds to wait for a connection                         |

    In your Prisma schema:

    ```prisma theme={null}
    datasource db {
      provider = "postgresql"
      url      = env("DATABASE_URL")
    }
    ```

    Prisma manages its own connection pool internally. The `connection_limit` parameter controls the pool size per Prisma client instance.
  </Accordion>

  <Accordion title="Python — SQLAlchemy">
    ```python theme={null}
    import os
    from sqlalchemy import create_engine

    engine = create_engine(
        os.environ["DATABASE_URL"],

        # Pool sizing
        pool_size=10,
        max_overflow=5,

        # Connection lifecycle
        pool_recycle=600,       # 10 min — recycle connections before proxy timeout
        pool_timeout=30,        # 30s — wait for available connection
        pool_pre_ping=True,     # verify connections before use

        # Disable prepared statements for PgBouncer transaction mode
        # (uncomment if using transaction mode)
        # connect_args={"prepare_threshold": None},  # for psycopg3
        # connect_args={"options": "-c plan_cache_mode=force_custom_plan"},  # alternative
    )
    ```

    `pool_recycle` is the max connection lifetime — SQLAlchemy will close and replace connections older than this value.

    `pool_pre_ping` issues a lightweight `SELECT 1` before each connection checkout. This adds a small round-trip but catches stale connections before your query fails.
  </Accordion>

  <Accordion title="Python — psycopg3 connection pool">
    ```python theme={null}
    import os
    from psycopg_pool import ConnectionPool

    pool = ConnectionPool(
        conninfo=os.environ["DATABASE_URL"],

        # Pool sizing
        min_size=2,
        max_size=10,

        # Connection lifecycle
        max_lifetime=600,       # 10 min, stays ahead of PgBouncer's 600s idle timeout
        max_idle=300,           # 5 min — close idle connections
        reconnect_timeout=5,

        # Disable prepared statements for PgBouncer transaction mode
        # (uncomment if using transaction mode)
        # kwargs={"prepare_threshold": None},
    )
    ```
  </Accordion>

  <Accordion title="Go — database/sql with pgx">
    ```go theme={null}
    import (
        "database/sql"
        "os"
        "time"

        _ "github.com/jackc/pgx/v5/stdlib"
    )

    // Open the connection pool.
    db, err := sql.Open("pgx", os.Getenv("DATABASE_URL"))
    if err != nil {
        log.Fatal(err)
    }

    // Pool sizing
    db.SetMaxOpenConns(10)
    db.SetMaxIdleConns(5)

    // Connection lifecycle
    db.SetConnMaxLifetime(10 * time.Minute) // recycle before proxy timeout
    db.SetConnMaxIdleTime(5 * time.Minute)  // close idle connections
    ```

    Go's `database/sql` handles connection recycling natively. `SetConnMaxLifetime` is the key setting — it ensures no connection is reused beyond the specified duration.

    To disable prepared statements for PgBouncer transaction mode, use the `default_query_exec_mode` connection parameter:

    ```go theme={null}
    connStr := os.Getenv("DATABASE_URL") + "?default_query_exec_mode=exec"
    db, err := sql.Open("pgx", connStr)
    ```
  </Accordion>

  <Accordion title="Ruby — ActiveRecord (Rails)">
    ```yaml theme={null}
    # config/database.yml
    production:
      url: ENV["DATABASE_URL"]
      pool: ENV.fetch("RAILS_MAX_THREADS", 5)
      idle_timeout: 300           # 5 min — close idle connections
      checkout_timeout: 5
      prepared_statements: false  # required for PgBouncer transaction mode
    ```

    For connection max lifetime, Rails 8.1+ supports `max_age` natively:

    ```yaml theme={null}
    # config/database.yml (Rails 8.1+)
    production:
      url: ENV["DATABASE_URL"]
      pool: ENV.fetch("RAILS_MAX_THREADS", 5)
      max_age: 600                # 10 min — recycle before proxy timeout
      idle_timeout: 300
      checkout_timeout: 5
      prepared_statements: false
    ```

    On older Rails versions, there is no built-in max connection age. Connections will still be recycled by the idle timeout if your app has enough traffic, but long-lived busy connections won't be recycled until they encounter an error.
  </Accordion>

  <Accordion title="Elixir/Phoenix — Ecto">
    ```elixir theme={null}
    # config/runtime.exs
    config :my_app, MyApp.Repo,
      url: System.fetch_env!("DATABASE_URL"),
      pool_size: 8,
      max_lifetime: 540_000..600_000,  # max connection lifetime; the range staggers reconnects
      prepare: :unnamed   # required for PgBouncer transaction mode
    ```

    For comprehensive Phoenix setup including migrations, Oban configuration, and Ecto-specific troubleshooting, see the [Phoenix with Managed Postgres](/postgres/guides-examples/phoenix-guide) guide.

    <Info>
      **Note on connection lifetime in Ecto:** `:max_lifetime` requires DBConnection 2.10.0 or later (2.10.1+ if your connections sit idle). It takes a range in milliseconds rather than a single value, so reconnects are spread out instead of the whole pool expiring at once. MPG's PgBouncer closes client connections after 600s idle (`client_idle_timeout`) and retires its own server connections after 600s (`server_lifetime`). Recycling on a 9-10 minute schedule keeps your pool ahead of both, so connections are replaced on your terms instead of turning up closed mid-query.
    </Info>
  </Accordion>
</AccordionGroup>

## Connection limits

Each MPG plan has a fixed number of PgBouncer connection slots shared across all clients. If your total pool size (across all app processes) exceeds this limit, new connections will be queued or rejected.

| Plan        | Max client connections | Max database connections | Reserve pool |
| ----------- | ---------------------- | ------------------------ | ------------ |
| Basic       | 200                    | 50                       | 10           |
| Starter     | 200                    | 50                       | 10           |
| Launch      | 500                    | 150                      | 30           |
| Scale       | 1000                   | 300                      | 50           |
| Performance | 1000                   | 300                      | 50           |

**Max client connections** is the total number of client connections PgBouncer will accept. **Max database connections** is the number of actual connections PgBouncer opens to PostgreSQL. The reserve pool handles bursts above the normal pool size.

### Common connection limit errors

**`FATAL: too many connections for role`** or **`remaining connection slots are reserved for roles with the SUPERUSER attribute`**: Your total pool size across all processes exceeds the PgBouncer connection limit. To fix:

* Reduce `pool_size` / `max` in each process
* Switch to **transaction** pool mode for better connection reuse
* Check for connection leaks (connections opened but never returned to the pool)

**Calculating your total pool usage:** If you have 3 web processes with `pool_size: 10` and 2 worker processes with `pool_size: 5`, your total is `(3 × 10) + (2 × 5) = 40` connections.

## Troubleshooting

<h3 id="tcp-recv-idle-closed-or-tcp-recv-idle-timeout">
  `tcp recv (idle): closed` or `tcp recv (idle): timeout`
</h3>

**Cause:** PgBouncer or the proxy closed an idle connection. MPG's PgBouncer closes client connections after 600s idle (`client_idle_timeout`). Proxy deployments also drain connections when old instances shut down.

**Fix:** Set your client's idle timeout to **300 seconds** (5 min) and max connection lifetime to **600 seconds** (10 min), which keeps your pool ahead of PgBouncer's own idle timeout. Most connection pools reconnect automatically when a connection is closed, so these errors are transient. If you see them often, reduce your pool size so fewer connections sit idle.

<h3 id="econnreset-or-quot-connection-reset-by-peer-quot">
  `ECONNRESET` or "connection reset by peer"
</h3>

**Cause:** A long-lived connection was terminated by something upstream, such as a proxy restart draining its remaining connections.

**Fix:** Set max connection lifetime to **600 seconds** (10 min) or less, so your pool recycles connections on its own schedule. Enable retry logic with backoff for transient failures.

### Prepared statement errors

Errors like `prepared statement "..." does not exist`, `prepared statement "..." already exists`, or `protocol_violation` on login all point to the same root cause: your client is sending named prepared statements through PgBouncer in transaction mode. PgBouncer assigns a different backend connection per transaction, so prepared statements created on one connection aren't available on the next.

**Fix:** Disable named prepared statements in your client configuration:

* **Node.js (pg):** This is the default behavior — no change needed
* **Prisma:** Add `?pgbouncer=true` to your connection string
* **Python (psycopg3):** Set `prepare_threshold=None`
* **Go (pgx):** Use `default_query_exec_mode=exec`
* **Ruby (ActiveRecord):** Set `prepared_statements: false`
* **Elixir (Ecto):** Set `prepare: :unnamed`

### Connection hangs on startup

**Cause:** DNS resolution failure on Fly's internal IPv6 network. Your app can't resolve the `.flympg.net` address.

**Fix:** Ensure your app is configured for IPv6. For Elixir apps, see the [IPv6 settings guide](/elixir/getting-started#important-ipv6-settings). For other runtimes, verify that your DNS resolver supports AAAA records on the Fly private network.