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Internal DNS uses IPv6 upstream servers 

Since 26.0.0, IPv6 nameservers in the host's /etc/resolv.conf file
have been treated the same as IPv4 nameservers - the internal DNS
server will use them as upstream servers, they won't be left in the
container's resolv.conf. (So, there's no longer any race between
the internal server and IPv6 upstream servers when using musl-libc.)

Signed-off-by: Rob Murray <rob.murray@docker.com>
This commit is contained in:
Rob Murray 2024-05-16 12:05:14 +01:00
parent 3417ae120e
commit 9dacd32d30
1 changed files with 0 additions and 16 deletions
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@ -174,22 +174,6 @@ configuration.
| `--dns-opt` | A key-value pair representing a DNS option and its value. See your operating system's documentation for `resolv.conf` for valid options. |
| `--hostname` | The hostname a container uses for itself. Defaults to the container's ID if not specified. |
### Nameservers with IPv6 addresses
If the `/etc/resolv.conf` file on the host system contains one or more
nameserver entries with an IPv6 address, those nameserver entries get copied
over to `/etc/resolv.conf` in containers that you run.
For containers using musl libc (in other words, Alpine Linux), this results in
a race condition for hostname lookup. As a result, 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 sometimes result in a round trip to the external server being faster than local
resolution.
### Custom hosts
Your container will have lines in `/etc/hosts` which define the hostname of the