Neon•2w ago

Elixir ecto migrations fail with timeout

Hey there,
I am experimenting with neon for an app that is deployed on fly.io.

I set up my config according to the articles on neon.
https://neon.com/docs/guides/elixir-ecto

In my release I run my migrations (to create db and run migrations), standard mix release stuff.
Sometimes this works and sometimes not. It times out regularly even when there is not migrations to run as everything s up to date.

[error] Postgrex.Protocol (#PID<0.152.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (ep-xxxxxxx.xxxxxx.aws.neon.tech:5432): timeout
[error] :gen_statem #PID<0.152.0> terminating
** (DBConnection.ConnectionError) tcp connect (ep-xxxxxxx.xxxxxx.aws.neon.tech:5432): timeout
(db_connection 2.8.1) lib/db_connection/connection.ex:109: DBConnection.Connection.handle_event/4
(stdlib 6.2.2.2) gen_statem.erl:3737: :gen_statem.loop_state_callback/11
(stdlib 6.2.2.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
Process Label: "db_conn_1"
Queue: [internal: {:connect, :init}]
Postponed: []
The database for App.Repo couldn't be created: "command timed out"
[error] Postgrex.Protocol (#PID<0.159.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (ep-xxxxxxx.xxxxxx.aws.neon.tech:5432): timeout

[error] Postgrex.Protocol (#PID<0.152.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (ep-xxxxxxx.xxxxxx.aws.neon.tech:5432): timeout
[error] :gen_statem #PID<0.152.0> terminating
** (DBConnection.ConnectionError) tcp connect (ep-xxxxxxx.xxxxxx.aws.neon.tech:5432): timeout
(db_connection 2.8.1) lib/db_connection/connection.ex:109: DBConnection.Connection.handle_event/4
(stdlib 6.2.2.2) gen_statem.erl:3737: :gen_statem.loop_state_callback/11
(stdlib 6.2.2.2) proc_lib.erl:329: :proc_lib.init_p_do_apply/3
Process Label: "db_conn_1"
Queue: [internal: {:connect, :init}]
Postponed: []
The database for App.Repo couldn't be created: "command timed out"
[error] Postgrex.Protocol (#PID<0.159.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (ep-xxxxxxx.xxxxxx.aws.neon.tech:5432): timeout

Is there any recommended config for this?

Thank you

Neon

Connect from Elixir with Ecto to Neon - Neon Docs

This guide describes how to connect from an Elixir application with Ecto, which is a database wrapper and query generator for Elixir. Ecto provides an API and abstractions for interacting databases, e...

instant-harlequin•12/3/25, 2:28 PM

Hey!
Are you running these migrations over the pooled connection string? If so, that might be your issue. We recommend running migrations over a direct connection

primary-violetOP•12/3/25, 2:35 PM

I am not using the pooled connection.

primary-violetOP•12/3/25, 2:35 PM

As I said it sometimes works sometimes does not.

instant-harlequin•12/3/25, 2:50 PM

Mhm, sounds like an issue another user was having this week because of ipv6.
If you run this command from your fly.io instance, does it start failing after a bit?

primary-violetOP•12/3/25, 3:11 PM

It seems like it is related to the instance being idle. Now it doesn't seem to become active.

instant-harlequin•12/3/25, 3:18 PM

Your Neon database or the Fly.io instance?

primary-violetOP•12/3/25, 3:27 PM

The neon db.

primary-violetOP•12/3/25, 3:27 PM

When it is idle the migrations fail. When it is active they are fine. They don't seem to wake it up.

primary-violetOP•12/3/25, 3:35 PM

Actually sometimes even when it is active.

instant-harlequin•12/3/25, 5:10 PM

The database should be awoken as soon as you begin your migration (and cold starts average around 275ms), so it is unlikely to be the issue. Have you tried the script I sent above?