[Hayyan612]

Refs Dokploy/dokploy#5074

Adds the docs note that issue asks for, under Troubleshooting > Domains & Traefik > Getting "Bad Gateway Error", next to the existing Vite example.

A Next.js app built with output: "standalone" listens on process.env.HOSTNAME || '0.0.0.0' (packages/next/src/build/utils.ts), and Docker sets HOSTNAME to the container ID. For a Compose service with a domain, addDokployNetworkToService attaches both dokploy-network and default, so the ID has two entries in /etc/hosts and the app binds only one of them. Traefik dials the dokploy-network address (traefik.docker.network=dokploy-network), so deploys that bind the default network address return Bad Gateway until the next redeploy.

Reproduction

Docker 28.5, Compose 2.40. A Compose service on [dokploy-network, default], the shape Dokploy generates, running a server that picks its host the same way as Next.js standalone, requested from a separate container on dokploy-network via the service's dokploy-network IP, as Traefik does:

HOSTNAME=<container id>, 8 fresh deploys:
bound=172.21.0.2  dokploy-network ip=172.20.0.2  -> ECONNREFUSED
bound=172.20.0.2  dokploy-network ip=172.20.0.2  -> 200
bound=172.20.0.2  dokploy-network ip=172.20.0.2  -> 200
bound=172.20.0.2  dokploy-network ip=172.20.0.2  -> 200
bound=172.21.0.2  dokploy-network ip=172.20.0.2  -> ECONNREFUSED
bound=172.21.0.2  dokploy-network ip=172.20.0.2  -> ECONNREFUSED
bound=172.20.0.2  dokploy-network ip=172.20.0.2  -> 200
bound=172.20.0.2  dokploy-network ip=172.20.0.2  -> 200

HOSTNAME=0.0.0.0, 4 fresh deploys: bound=0.0.0.0 -> 200 every time

Both fixes in the note were checked: ENV HOSTNAME="0.0.0.0" in the image and environment: HOSTNAME=0.0.0.0 in Compose each override Docker's default, and the container's hostname itself is unchanged. The Dockerfile form matches the official Next.js Docker example.