kevinveenbirkenbachandClaude Opus 5 52b4504035 fix(container-dns): let the bridge be declared instead of guessed ...

Whether a resolver answers on the docker bridge was inferred from the host's
own resolv.conf: all entries loopback was read as "a listener of ours is there,
and containers must reach it on the bridge". A systemd-resolved stub binds
127.0.0.53, NetworkManager's dnsmasq binds 127.0.0.1, and a node dnsmasq binds
both those and the bridge. All three look identical from resolv.conf and only
the third is reachable from a container.

So ordinary hosts were handed an address with nothing behind it. The
Instructions job died there: daemon.json carried "dns": ["10.208.0.1"] alone,
and the openresty build could not resolve dl-cdn.alpinelinux.org while the
daemon, resolving through the host, pulled the same base image fine. Two netns,
two outcomes.

e308e18923 had already fixed this once, with a reachability gate whose message
names the same URL. b09f2cbd82 dropped that gate and ce43263745 put the
resolv.conf inference in its place, so the guard was gone and only the missing
docker0 fact still hid it. 285ba1e76c removed that accident and the failure
surfaced.

svc-net-tor and NETWORK_CONTAINER_BRIDGE_RESOLVER now say it instead, the
latter false by default and true in the swarm lab, which provisions the dnsmasq
its nodes resolve through. Extra-vars are global, so the lab's NFS and backup
hosts carry it although no listener is installed there; the clearnet resolver
behind the bridge keeps them working.

The docker0 fact is gone from the address too. It is not merely late, it is
wrong while it is late: facts are read before the daemon config is applied, so
docker0 still holds docker's default and writing default-address-pools moves
the bridge out from under it. A swarm node shipped "dns": ["172.17.0.1", ...]
against a live 10.208.0.1, which is why its containers asked a dead address and
fell through to the public resolver, where infinito.example does not exist. The
pool answers before the daemon exists and answers the same afterwards, and it
is read per slice rather than per supernet, which differ once a pool does not
start on a slice boundary.

A list that would carry only the bridge now gets NETWORK_PUBLIC_DNS_RESOLVERS
behind it, so a declaration that turns out to be wrong costs a wasted first
query rather than all name resolution. An empty declaration raises.

Rendered from the repository's own variable files: the Instructions host yields
[] and the template omits the key, which is what de95a95c65 emitted while that
job was green; lab and tor nodes yield the live bridge ahead of the clearnet
resolver even with a stale docker0 fact present; an ordinary host yields only
its declared resolver.

The suite asserted the two behaviours this replaces, including one case added
with 285ba1e76c demanding the stale fact win. They are inverted, and a
cross-product over nameserver shapes, tor membership, clearnet and the docker0
fact now asserts that no shape ends up holding the bridge alone - the old suite
checked each shape by itself, which is how this passed through it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

2026-08-30 00:32:13 +02:00

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2026-08-29 00:55:22 +02:00

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fix(container-dns): let the bridge be declared instead of guessed

2026-08-30 00:32:13 +02:00

__init__.py

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