Fly.io Proxy

Public reverse proxy on Fly.io that exposes selected BlumeOps services to the internet via a Tailscale tunnel back to the homelab.

Quick Reference

Property	Value
App	blumeops-proxy
Region	sjc (San Jose)
Fly.io URL	blumeops-proxy.fly.dev
Config	fly/ directory in repo
IaC	fly/fly.toml (app), Pulumi (DNS + auth key)

Exposed Services

Public domain	Backend (via Caddy)	Service
docs.eblu.me	docs.ops.eblu.me	docs
cv.eblu.me	cv.ops.eblu.me	cv
forge.eblu.me	forge.ops.eblu.me	forgejo

Architecture

Internet traffic hits Fly.io’s Anycast edge, terminates TLS with a Let’s Encrypt certificate, and is proxied by nginx to caddy on indri over a direct Tailscale WireGuard tunnel. Caddy then routes to the actual service. See expose-service-publicly for the full architecture diagram.

Why Caddy, not per-service Tailscale Ingress?

Previously, nginx connected directly to each service’s *.tail8d86e.ts.net Tailscale Ingress endpoint. This caused 20+ second latency because the Tailscale Ingress pods (running inside k8s) are behind pod-network NAT and can only reach the Fly VM via Tailscale DERP relay servers — not direct WireGuard peering.

Routing through Caddy on indri solves this because indri’s host-level Tailscale can establish direct WireGuard connections with the Fly VM (45ms round trip). This generalizes to all services regardless of where they run (native on indri, minikube, or ringtail k3s), since Caddy already routes to everything.

Direct WireGuard Peering

The Fly VM pins its Tailscale WireGuard listener to port 41641 (tailscaled --port=41641). Combined with well-behaved NAT on both sides (MappingVariesByDestIP: false), this allows Tailscale to establish direct peer-to-peer connections via UDP hole punching — no dedicated IPv4 required.

If direct peering fails (observable via tailscale ping indri showing “via DERP”), allocate a dedicated IPv4 ($2/month) with fly ips allocate-v4 to provide a guaranteed inbound UDP path.

Key Files

File	Purpose
fly/fly.toml	App configuration
fly/Dockerfile	nginx + Tailscale + Alloy container
fly/nginx.conf	Reverse proxy, caching, rate limiting, JSON logging
fly/alloy.river	Alloy config: log tailing, metric extraction, remote_write
fly/start.sh	Entrypoint: start Tailscale, wait for MagicDNS, then nginx + Alloy
pulumi/tailscale/__main__.py	Auth key (tag:flyio-proxy)
pulumi/tailscale/policy.hujson	ACL grants for proxy
pulumi/gandi/__main__.py	DNS CNAMEs

Networking

Fly.io runs Firecracker microVMs which support TUN devices natively. Tailscale runs with a real TUN interface (not userspace networking), so MagicDNS and direct Tailscale IP routing work normally.

The tailscaled process is started with --port=41641 to pin the WireGuard listener to a fixed port. This is critical for direct peering — without it, hole punching is unreliable. A [[services]] block in fly.toml exposes this port as UDP, though it is only active when a dedicated IPv4 is allocated.

The Tailscale auth key is preauthorized=True to avoid device approval hangs on container restarts.

Observability

Alloy runs inside the container alongside nginx and Tailscale, providing:

• Logs: nginx JSON access logs tailed and pushed to Loki ({instance="flyio-proxy", job="flyio-nginx"})
• Metrics: Derived from access logs, pushed to Prometheus via remote_write
  • flyio_nginx_http_requests_total — request rate by status/method/host
  • flyio_nginx_http_request_duration_seconds — total request latency histogram (includes proxy overhead)
  • flyio_nginx_upstream_response_time_seconds — backend response time histogram (Forgejo processing only)
  • flyio_nginx_http_response_bytes_total — response bandwidth
  • flyio_nginx_cache_requests_total — cache HIT/MISS/EXPIRED counts

Dashboards

Dashboard	Purpose
Docs APM	Per-service view for docs.eblu.me: request rate, latency percentiles, cache hit ratio, error rate, bandwidth, access logs
Fly.io Proxy Health	Aggregate proxy health: connections, total request rate by host, cache performance, upstream latency, Alloy health

Alloy listens on 127.0.0.1:12345 for self-scraping its /metrics endpoint. All metrics carry instance="flyio-proxy".

Security Considerations

The tag:flyio-proxy ACL grants access only to tag:flyio-target:443. Indri carries this tag (for Caddy), and the k8s Tailscale Ingress pods for Loki and Prometheus also carry it so Alloy can push logs and metrics directly. A compromised proxy cannot route to arbitrary services on the tailnet — only tag:flyio-target endpoints on port 443.

Crawler Mitigation

The proxy serves a robots.txt blocking crawlers from expensive endpoints:

• /mirrors/ — large mirrored repos
• /user/ — auth endpoints (crawlers follow redirect loops)
• /users/ — user profile pages
• /*/archive/ — git bundle generation (DoS vector, see below)
• /*/releases/download/ — release artifacts

Archive requests (/<owner>/<repo>/archive/*) are 302-redirected to forge.ops.eblu.me (tailnet-only), preventing unauthenticated archive generation. This mitigates a known Forgejo DoS vector where crawlers requesting unique commit SHAs trigger unbounded git bundle generation.

Release downloads are cached at the proxy layer (7-day TTL, keyed by URI) to absorb repeated downloads of the same artifact.

To expose an additional service through the proxy, add a Caddy route for it and an nginx server block. See expose-service-publicly for the full workflow.

Spider Trap Mitigation

The SPA fallback (try_files ... /index.html) serves index.html with a 200 for any URI, including non-existent paths. Quartz’s relative links (../path) compound when resolved from phantom URLs, creating an infinite tree of unique URIs that crawlers follow indefinitely. In March 2026, Meta’s crawler (meta-externalagent/1.1) hit ~49,000 unique URIs over 7 hours this way.

Two nginx location guards in containers/quartz/default.conf mitigate the trap:

1. /tags/ depth limit — /tags/<name> is always flat; anything deeper returns 404.
2. Global depth-5 cutoff — real content never exceeds depth 4; paths with 5+ segments return 404.

These are applied in the Quartz container’s nginx config, not the Fly.io proxy. The proper fix is switching Quartz to root-absolute links (planned for the fork).

Secrets

Secret	Source	Description
TS_AUTHKEY	Pulumi state → fly secrets	Tailscale auth key for joining tailnet
FLY_DEPLOY_TOKEN	Fly.io → 1Password	Deploy token for CI

Related

• expose-service-publicly - Setup guide for adding new public services
• manage-flyio-proxy - Operational tasks (deploy, shutoff, troubleshoot)
• caddy - Private reverse proxy for *.ops.eblu.me (separate system)
• tailscale - WireGuard mesh network
• gandi - DNS hosting