Multiple domains for a single frankenphp caddy app results in endless 308 redirect

[samdark]

We have a production environment for which we need to migrate the domain name. We want to do this with 0 downtime and thought about simply adding a new domain to the setup and remove the old one later.

We are running a Symfony app using frankenPHP+caddy from a Wolfi docker image (ghcr.io/shyim/wolfi-php/frankenphp:8.3).

The problem that we face is that when we add the second domain we get 308 redirects that end in a loop for both domain names.

I've scoured the documentation and GitLab issues but can't find why this would not work, what I've tried:

domain1.com, domain2.com {
    root * /app/public
    encode zstd br gzip

    php_fastcgi unix//run/php/php8.3-fpm.sock
    file_server
}

Or separated:

domain1.com {
    root * /app/public
    encode zstd br gzip

    php_fastcgi unix//run/php/php8.3-fpm.sock
    file_server
}
domain2.com {
    root * /app/public
    encode zstd br gzip

    php_fastcgi unix//run/php/php8.3-fpm.sock
    file_server
}

Other attempts:

bypassing the php_fastcgi directive (using transport fastcgi, php_server or php)
disabling HTTPS (auto_https off)

Furthermore, I've tried every setting for the SERVER_NAME env:

SERVER_NAME=domain1.com,domain2.com
SERVER_NAME=
SERVER_NAME=*

But every permutation seems to end in the 308 (or bad gateway). I understood that internally a canonical host is determined and that that is causing the redirects - though that would not explain why we get 308's for both domains.

I feel I must be missing something simple, and I hope someone can point me in the right direction for pointing multiple domains to a single application like this?

[AlliBalliBaba]

308 indicates a redirect from http to https. I think if you only want http, you have explicitly also set the :80 port (haven't tried myself though)

domain1.com:80, domain2.com:80 {
    ...
}

[TwindoAI]

You're absolutely right, having auto_https off was not enough.
We tried the explicit port definition before, but it failed because of another config issue and was discarded.

Thank you!