Problems with NAT loopback

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Hi

For some time I have played around with Nextcloud and finally I got some time to set Nextcloud up on what I would call my ‘production’

I’m using a Minisforum MS-01 I5, 32gb ram 128gb boot and 3x4TB nvme for the storage.
Using docker and the compose.yaml from github - Actually a copy of one that I have deplyed a few times so I would have expected it to work - For sure, there is the Mime type update warining - Why is this still there?

but his time I also got:

Data directory protected

Could not check that the data directory is protected. Please check manually that your server does not allow access to the data directory. To allow this check to run you have to make sure that your Web server can connect to itself. Therefore it must be able to resolve and connect to at least one of its `trusted_domains` or the `overwrite.cli.url`. This failure may be the result of a server-side DNS mismatch or outbound firewall rule.

  • JavaScript source map support

    Your webserver is not set up to serve `.js.map` files. Without these files, JavaScript Source Maps won’t function properly, making it more challenging to troubleshoot and debug any issues that may arise.

  • JavaScript modules support

    Unable to run check for JavaScript support. Please remedy or confirm manually if your webserver serves `.mjs` files using the JavaScript MIME type. To allow this check to run you have to make sure that your Web server can connect to itself. Therefore it must be able to resolve and connect to at least one of its `trusted_domains` or the `overwrite.cli.url`. This failure may be the result of a server-side DNS mismatch or outbound firewall rule.

  • OCS provider resolving

    Could not check if your web server properly resolves the OCM and OCS provider URLs. To allow this check to run you have to make sure that your Web server can connect to itself. Therefore it must be able to resolve and connect to at least one of its `trusted_domains` or the `overwrite.cli.url`. This failure may be the result of a server-side DNS mismatch or outbound firewall rule.

This I have always seen on all AIO installation i have made so far.

  • Errors in the log

    3 errors in the logs since January 24, 2026, 3:51:02 PM

I know that the above is just warnings, but why ?

I just spin up a few containers that is created / maintained by Nextcloud, so why do I see these errors that is out of my control ?

The Basics

  • Nextcloud Server version (e.g., 29.x.x):
  • Operating system and version (e.g., Ubuntu 24.04):
    • Ubuntu 24.04
  • Web server and version (e.g, Apache 2.4.25):
    • in AIO
  • Reverse proxy and version _(e.g. nginx 1.27.2)
    • Nginx Reverse Proxy Manager
  • PHP version (e.g, 8.3):
    • provided in AIO
  • Is this the first time you’ve seen this error? (Yes / No):
    • replace me
  • When did this problem seem to first start?
    • right after installation
  • Installation method (e.g. AlO, NCP, Bare Metal/Archive, etc.)
    • AIO
  • Are you using CloudfIare, mod_security, or similar? (Yes / No)
    • No

Summary of the issue you are facing:

Strange warnings on a new installation

Steps to replicate it (hint: details matter!

Use the compose.yaml and then simply : docker compose up -d

2

Please use search and review setup_warning tag for many similar topics.

the warnings you describe include a link to a documentation which is often enough to fix the issues. and no this error are completely in your control .e.g nginx requires specific mime type config to server mjs files which you likely didn’t apply.

3

How can it be in my control ?

I did not not create the AIO containers.

Sure I can fix it, that is not my point.