docker-compose.yml: `network_mode: host` doesn't work on macOS

[ttilberg]

The generated docker-compose.yml uses network_mode: host for Prometheus, which doesn't work on macOS Docker Desktop.

On Mac, Docker runs in a Linux VM, so "host" refers to the VM's network, not the Mac's localhost.

This causes exceptions when trying to navigate to "uptime" or "status":

Prometheus::ApiClient::Client::RequestError (Failed to open TCP connection to localhost:9090 (Connection refused))

I fixed this by replacing network_mode: host with a port mapping in the docker compose file:

prometheus:
  image: prom/prometheus:v3.4.1
  container_name: uptime-prometheus
  ports:
    - "9090:9090"
  volumes:
    # ...

If the network_mode: host config is important for reasons I haven't yet discovered, maybe a comment in the file for Docker Desktop users (macos/windows) could be helpful to help guide macos developers.

And/or a mention in the readme about some of these macos environment differences I've been finding.

Environment:

• macOS (Docker Desktop)

[lewispb]

We went with replacing network_mode: host with explicit port mapping + extra_hosts for host.docker.internal:

prometheus:
  ports:
    - "9090:9090"
  extra_hosts:
    - "host.docker.internal:host-gateway"

The Prometheus scrape config now targets host.docker.internal:9394 instead of localhost:9394, so Prometheus can still reach the Rails app on the host.

This works cross-platform:

• macOS/Windows Docker Desktop: host.docker.internal is natively supported
• Linux Docker Engine 20.10+: host-gateway resolves to the host IP

PR: #54