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Document NSS plugin limitations #4034

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Feb 9, 2024
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Document NSS plugin limitations #4034

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25 changes: 25 additions & 0 deletions docs/external-runtime-deps.md
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Expand Up @@ -150,6 +150,31 @@ Optional cgroup controllers:
[cgroup v1]: https://www.kernel.org/doc/html/v5.16/admin-guide/cgroup-v1/
[cgroup v2]: https://www.kernel.org/doc/html/v5.16/admin-guide/cgroup-v2.html

### No integration with Name Service Switch (NSS) APIs

The k0s Linux binaries are by default statically linked against [musl libc].
This includes the binaries distributed on the GitHub releases pages. Static
linking ensures that k0s can run seamlessly across a wide range of Linux
environments by not requiring a specific standard C library to be installed on
the host system. However, this design choice means that k0s cannot use [glibc's
NSS APIs], which require dynamic linking.

This limitation is particularly relevant when a system uses NSS plugins, such as
[nss-myhostname], for resolving network names like `localhost`. Systems lacking
a dedicated stub resolver capable of handling `localhost` DNS queries
specifically will encounter issues running k0s. To mitigate this, users are
advised to either activate a stub DNS resolver, such as `systemd-resolved`, or
to manually add `localhost` entries to the `/etc/hosts` file as shown below:

```text
127.0.0.1 localhost
::1 localhost
```

[musl libc]: https://musl.libc.org/
[glibc's NSS APIs]: https://www.gnu.org/software/libc/manual/html_node/Name-Service-Switch.html
[nss-myhostname]: https://www.freedesktop.org/software/systemd/man/latest/nss-myhostname.html

### External hard dependencies

There are very few external tools that are needed or used.
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