Add a lightweight Docker healthcheck

[llaumgui]

Hi,

If you're interested, I can work on a Pull Request to integrate s6-overlay. This would allow us to:

• Optimize startup performance: Run entrypoint initialization operations once at container startup rather than on every invocation.
• User/Group customization: Allow custom PUID and PGID configuration.
• Enhanced secrets management: Support the FILE__ prefix pattern for secrets to avoid exposing sensitive data in environment variables.
• ...and more.

You can check an example of how I implemented this in one of my Docker images: https://github.com/llaumgui/docker-images-nextcloud-php-fpm/tree/main/8.5/rootfs

Additionally, I would be happy to help add a healthcheck. Is there an existing API endpoint such as /api/health that we could use for this?

[themartz90]

Hey! Thanks for offering and for linking your implementation. I had a look through it and the s6-overlay documentation.
Jellydash does not currently have a health endpoint. A focused healthcheck PR would be useful, and you’re welcome to work on that first.

Could we keep the first PR limited to:

• A public, unauthenticated /api/health.php endpoint
• JSON with HTTP 200 when Jellydash and its configured database are responsive
• HTTP 503 with a generic response when the database is unavailable
• A lightweight SELECT 1 check compatible with both MariaDB and SQLite
• No Jellyfin, Jellyseerr, or other external service checks
• No schema changes, detailed errors, or sensitive configuration in the response
• A Docker image healthcheck and suitable test coverage

Please keep s6-overlay, PUID/PGID, FILE__ secrets, and other changes outside this first PR.
The current entrypoint already runs once per container startup, so s6 would mainly help with process supervision rather than startup performance.
Jellydash also uses Apache, publishes AMD64 and ARM64 images, and has special one-off database migration behavior. I would therefore like to consider s6 separately after the healthcheck.

Please base the PR on the current main branch and implement it specifically for Jellydash rather than copying the PHP-FPM helpers. Thanks!