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Zero-downtime Fly.io deploys: bluegreen + startup reorder

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Three changes to eliminate 502s during proxy deploys:

1. Start nginx after Tailscale connects (not before) so MagicDNS is
   always available when the first request arrives. This is the
   community-recommended pattern for Tailscale sidecars on Fly.io.

2. Switch deploy strategy to bluegreen — the old machine keeps serving
   traffic until the new one passes health checks, then Fly.io cuts
   over. Rolling deploys with a single machine always cause downtime.

3. Replace top-level [checks] with [[http_service.checks]]. Top-level
   checks only monitor; they don't gate traffic routing. Service-level
   checks tell the Fly Proxy to hold traffic until the app is ready.

The sentinel file (/tmp/tailscale-ready) and nginx if-check are removed
since nginx no longer starts before Tailscale.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
Erich Blume 2026-02-09 11:31:52 -08:00
commit 4bbe4e7c20
4 changed files with 20 additions and 24 deletions
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Eliminate 502 errors during Fly.io proxy deploys by starting nginx after Tailscale, switching to bluegreen deploys, and using service-level health checks for traffic gating.