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Merge pull request #20049 from robmry/networking_intro_dns_fixes 

Networking overview - DNS fixes
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David Karlsson 2024-05-17 13:18:18 +02:00 committed by GitHub
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@ -167,28 +167,12 @@ You can configure DNS resolution on a per-container basis, using flags for the
The following table describes the available `docker run` flags related to DNS
configuration.
| Flag | Description |
| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `--dns` | The IP address of a DNS server. To specify multiple DNS servers, use multiple `--dns` flags. If the container can't reach any of the IP addresses you specify, it uses Google's public DNS server at `8.8.8.8`. This allows containers to resolve internet domains. |
| `--dns-search` | A DNS search domain to search non-fully qualified hostnames. To specify multiple DNS search prefixes, use multiple `--dns-search` flags. |
| `--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.
| Flag | Description |
| -------------- |-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `--dns` | The IP address of a DNS server. To specify multiple DNS servers, use multiple `--dns` flags. DNS requests will be forwarded from the container's network namespace so, for example, `--dns=127.0.0.1` refers to the container's own loopback address. |
| `--dns-search` | A DNS search domain to search non-fully qualified hostnames. To specify multiple DNS search prefixes, use multiple `--dns-search` flags. |
| `--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. |
### Custom hosts