Fix docker-compose for macOS Docker Desktop

[lewispb]

Summary

• Replace network_mode: host with explicit port mapping (ports: "9090:9090") so Prometheus is reachable on macOS/Windows Docker Desktop
• Add extra_hosts: host.docker.internal:host-gateway so Prometheus can still scrape the Rails app running on the host
• Update Prometheus scrape configs to target host.docker.internal instead of localhost
• Apply the same fix to the test dummy's docker-compose and alertmanager service

Why

network_mode: host doesn't work on macOS Docker Desktop because Docker runs inside a Linux VM — "host" refers to the VM's network, not the Mac's localhost. This caused Prometheus::ApiClient::Client::RequestError (Connection refused) when navigating to uptime/status pages.

The host.docker.internal + host-gateway approach works cross-platform: natively on Docker Desktop (macOS/Windows), and via the host-gateway directive on Linux Docker Engine 20.10+.

Test plan

• bin/smoke_test passes — all checks pass including generator output, server boot, metrics, and probe execution
• Verified the generated docker-compose.yml contains the correct port mapping and extra_hosts
• Test on macOS Docker Desktop to confirm Prometheus is reachable

Fixes #28

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR updates Upright’s docker-compose setup to work on macOS/Windows Docker Desktop by removing network_mode: host, exposing Prometheus/Alertmanager via port mappings, and switching Prometheus scrape targets to host.docker.internal.

Changes:

• Replace network_mode: host with explicit ports mapping and add extra_hosts: host.docker.internal:host-gateway for Prometheus.
• Update Prometheus scrape configuration to target host.docker.internal instead of localhost.
• Bump gem version to 0.3.0 and reflect it in Gemfile.lock.

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Reviewed changes

Copilot reviewed 5 out of 6 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/dummy/docker-compose.yml	Switch dummy Prometheus/Alertmanager off host networking and expose ports.
test/dummy/config/prometheus.yml	Update dummy scrape target to host.docker.internal:9394.
lib/generators/upright/install/templates/docker-compose.yml	Apply the same docker-compose networking changes to the install generator template.
lib/generators/upright/install/templates/development_prometheus.yml	Update generated dev Prometheus scrape target to host.docker.internal:9394.
lib/upright/version.rb	Bump Upright version to 0.3.0.
Gemfile.lock	Update locked Upright version references to 0.3.0.

---

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[Copilot]

extra_hosts: host.docker.internal:host-gateway relies on Docker Engine 20.10+ (and a Compose implementation that supports the special host-gateway value). Consider adding an inline comment or note in the dummy compose file about this minimum requirement and the fallback (upgrade Docker or switch back to network_mode: host on Linux) to avoid confusing startup errors on older Docker installs.

Suggested change

	- "9090:9090"
	- "9090:9090"
	# `host-gateway` requires Docker Engine 20.10+ and a Compose implementation
	# that supports the special value. On older Linux Docker setups, upgrade
	# Docker/Compose or switch back to `network_mode: host`.

[Copilot]

The template uses extra_hosts: host.docker.internal:host-gateway, which requires Docker Engine 20.10+ (and a Compose implementation that supports host-gateway). Please document this requirement in the generated compose (or nearby docs) and provide a clear fallback for older Linux Docker setups to prevent hard-to-diagnose failures when bringing the stack up.

Suggested change

	- "9090:9090"
	- "9090:9090"
	# Requires Docker Engine 20.10+ and a Compose implementation that supports
	# the special `host-gateway` value in `extra_hosts`.
	#
	# If `docker compose up` fails on an older Linux Docker setup, replace
	# `host-gateway` below with your Docker host gateway IP (for example
	# `172.17.0.1`, adjusted for your environment).

[Copilot]

This scrape target is now Docker-specific (host.docker.internal). If someone runs Prometheus directly on the host (not in Docker), this hostname won’t resolve. Consider adding a brief comment in this config (or maintaining a separate non-Docker example) to clarify when host.docker.internal vs localhost should be used.

Suggested change

	static_configs:
	static_configs:
	# Use `host.docker.internal` when Prometheus runs in Docker.
	# If Prometheus runs directly on the host, use `localhost:9394` instead.

[Copilot]

The development Prometheus config now targets host.docker.internal, which is correct for Dockerized Prometheus scraping a host-run Rails app, but it diverges from the localhost:9394 example in the README. Consider adding an explanatory comment here (or updating the docs) to make it clear which target to use in each setup.

Suggested change

	static_configs:
	static_configs:
	# Use host.docker.internal when Prometheus runs in Docker and Rails runs on the host.
	# If Prometheus also runs directly on the host, use localhost:9394 instead.

[Copilot]

The PR description focuses on docker-compose/macOS fixes, but it also bumps the gem version to 0.3.0. Please either mention the version bump explicitly in the PR description (and ensure release notes/changelog capture this docker-compose change), or split the version bump into a separate release PR to keep scope clear.