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engine: external ipv6 dns server race condition 

Signed-off-by: David Karlsson <david.karlsson@docker.com>
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David Karlsson 2023-05-12 16:26:54 +02:00
parent 8c3573f2c1
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network/index.md
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@ -120,6 +120,23 @@ as follows:
2. The container uses the first response returned by any of the nameservers. 2. The container uses the first response returned by any of the nameservers.
Even if the first response is `NXDOMAIN`, or similar. Even if the first response is `NXDOMAIN`, or similar.
### IPv6 name resolution
The embedded DNS server handles both IPv4 and IPv6 name resolution. However,
there is a caveat in name resolution for IPv6.
Any IPv6 addresses specified in the `/etc/resolv.conf` file on the host system
get copied over to the `/etc/resolv.conf` file in containers that you run.
For containers running on musl libc (Alpine Linux), hostname resolution might
sporadically fail if the external IPv6 DNS server wins the race condition
against the embedded DNS server.
It's rare that the external DNS server is faster than the embedded one. But
things like garbage collection, or large numbers of concurrent DNS requests,
can result in a roundtrip to the external server be faster than the local
resolution, on some occasions.
### Custom hosts ### Custom hosts
Custom hosts, defined in `/etc/hosts` on the host machine, aren't inherited by containers. Custom hosts, defined in `/etc/hosts` on the host machine, aren't inherited by containers.