fix(gateway): bind to IPv6 dual-stack for Railway private networking - #227
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Railway's private networking (`*.railway.internal`) resolves to IPv6 addresses. The default `0.0.0.0` bind is IPv4-only and rejects internal service-to-service connections with ECONNREFUSED — observed when the web service proxies /mcp, /v1/*, etc. to the gateway via the single-origin rewrites added in ADR 0009. Binding to `::` (IPv6 unspecified) enables dual-stack mode, accepting both IPv4 and IPv6 traffic through the same socket. Public ingress (Railway edge → container) keeps working; docker-compose and local `pnpm dev` are unaffected because loopback works on both stacks.
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Summary
After #226 (single-origin gateway) shipped, production hit
ECONNREFUSEDwhen the web service tried to proxy/mcp,/v1/*, etc. to the gateway over Railway's private network.Root cause: Railway's private DNS (e.g.
gateway.railway.internal) resolves to IPv6 addresses.@hono/node-server's default bind is0.0.0.0which is IPv4-only, so internal traffic was rejected even though public ingress worked.Fix
One-line change in apps/gateway/src/main.ts — pass
hostname: '::'toserve(). This binds the gateway in IPv6 dual-stack mode, which accepts BOTH IPv4 and IPv6 connections through the same socket on Linux. No other change needed.What's unaffected
gateway:8080inside the compose network already worked over IPv4; it now also works over IPv6 (which compose doesn't use, but harmless).pnpm dev: loopback on::1and127.0.0.1both reach the gateway.Test plan
pnpm -F @holo/gateway typecheck— cleanWEB_BASE_URL=https://holobase.dev pnpm verify:gatewayreturns 6 green checkshttps://holobase.dev/mcpround-trips (the operator gate from ADR 0009)🤖 Generated with Claude Code