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Host services

App code in a container has its own loopback, so DB_HOST=127.0.0.1 points at the app container, not at MySQL on the host. There are three ways to reach what lives outside the container.

Services on the host: host.docker.internal

Add host.docker.internal to the service in docker-compose.yml and point .env at it:

services:
  app:
    extra_hosts:
      - "host.docker.internal:host-gateway"

DB_HOST=host.docker.internal

srv doctor warns when it finds *_HOST=127.0.0.1-style entries in a container-backed site's .env.

Services in another compose stack: srv network attach

Join the site to that stack's network and address its containers by name:

srv network attach my-app mysql01_default
srv network detach my-app mysql01_default
srv network list my-app

The network must already exist. Run srv restart SITE after attaching.

Host files and binaries: srv volume add

Mount what the app needs, such as ffmpeg, a shared temp directory or a Nix profile:

srv volume add my-app ~/.nix-profile:/home/$USER/.nix-profile:ro
srv volume add my-app /nix:/nix:ro
srv volume list my-app
srv volume remove my-app /nix

Mount paths must be absolute (~ is expanded), and /app is reserved for the project itself.