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Let's use getent ahosts instead of dig +short #355

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vazhnov opened this issue Dec 9, 2024 · 2 comments
Open

Let's use getent ahosts instead of dig +short #355

vazhnov opened this issue Dec 9, 2024 · 2 comments
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@vazhnov
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vazhnov commented Dec 9, 2024 •
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Hello!

Thank you for the project!

I recommend to use getent ahosts NAME instead of dig +short NAME in this course, for both: manual steps in the documentation and scripts.

getent is a tool usually included into even very minimalistic OS setup.

getent follows /etc/nsswitch.conf rules (reads /etc/hosts, mDNS, etc.), while dig is mainly designed to troubleshoot external DNS servers. Much more details about the difference can be found in https://unix.stackexchange.com/questions/20784/ (or in my brief summary).

I think using dig is a bad practice when custom records in /etc/hosts are used. getent is designed for such cases.

I'm currently in step 08 and I see no issues with this replacement.

Also I've checked: using getent ahosts is compatible with both Vagrant images, Ubuntu and Debian, to do steps of this course.

Currently script vagrant/ubuntu/update-dns.sh fails to apply in Debian let's skip this for dedicated issue.
@vazhnov vazhnov added the bug Something isn't working label Dec 9, 2024
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I'm using dig +short because it returns only the IP address with no need to muck about with awk to get it. getent will return IP+HOST
The lab's not millisecond performance critical so if dig does waste time getting a negative response from DNS before checking hosts file, not really an issue.

@vazhnov
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vazhnov commented Dec 10, 2024

I'm using dig +short because it returns only the IP address with no need to muck about with awk to get it. getent will return IP+HOST

I agree, I have to use getent ahosts example.com | awk '{ print $1 ; exit }' to return only one IP-address without name.

The lab's not millisecond performance critical so if dig does waste time getting a negative response from DNS before checking hosts file, not really an issue.

The thing is — dig doesn't use /etc/hosts at all. In case of the lab, I think that systemd-resolved is doing that.

This change is also about to teach people to use proper tools.

vazhnov added a commit to vazhnov/kubernetes-the-hard-way__vagrant that referenced this issue Dec 18, 2024
@vazhnov
Use getent ahosts everywhere because it follows `/etc/nsswitch.conf…
d0dab69 
…` rules (reads `/etc/hosts`, mDNS, etc.), instead of `dig +short`

See mmumshad#355
@vazhnov vazhnov mentioned this issue Dec 19, 2024
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@vazhnov vazhnov mentioned this issue Jan 3, 2025
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vazhnov added a commit to vazhnov/kubernetes-the-hard-way__vagrant that referenced this issue Jan 15, 2025
@vazhnov
Merge pull request #2 from vazhnov/changes_2024-12
f65f8ae 
Multiple changes 2024-12:

* Added GitHub actions [Differential ShellCheck](https://github.com/redhat-plumbers-in-action/differential-shellcheck).
    + I had to add temporary SC2166 and SC2059 to ShellCheck ignored because there are too much changes I have to do.
* Fixed a bunch of linter warnings in Bash scripts.
* Added compatibility with Vagrant Debian image guests.
* The new code should be compatible with both Ubuntu and Debian Vagrant images (was: Ubuntu only).
* Use Debian images instead of Ubuntu — less memory consumption, less services to disable, no Snap.
* Stop and disable extra services, no need in auto-update on the lab guest VMs:
    + motd-news.timer
    + ubuntu-advantage.service
    + apt-daily.timer
    + apt-daily.service
    + unattended-upgrades.service
* Replaced all `dig +short NAME` to `getent ahosts example.com | awk '{ print $1 ; exit }'`
    + because it follows `/etc/nsswitch.conf` rules (reads `/etc/hosts`, mDNS, etc.), see mmumshad#355.
* Fix typo in `docs/04-certificate-authority.md`: `SERVICE_CIDR` should be `10.96.0.0/16`.
* No need in `resolvConf` in `docs/10-bootstrapping-kubernetes-workers.md` and in `docs/11-tls-bootstrapping-kubernetes-workers.md` for Debian guests.
* `cert_verify.sh` checks certificate in the current directory (was: all certs must be in `$HOME`), add new variable `WORKDIR`.
* All interactive `apt` commands: remove `-y` argument, because these commands are executed interactively.
* Add `gpg` and `--no-install-recommends` to `apt-get install -y apt-transport-https ca-certificates curl` in `docs/09-install-cri-workers.md`.
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