Speed up namespace switching in big clusters

[imbstack]

Hi, thank you so much for this tool, it is the best one of its kind!

This patch just switches the check that a namespace exists from listing all namespaces to seeing if a specific label exists. This doesn't make much difference on clusters with reasonable numbers of namespaces but for me it is roughly a 8 second speedup:

$ time (kubechn namespace)      
Context "context" modified.
Switched to namespace "namespace"
( kubechn namespace; )  5.32s user 0.23s system 61% cpu 8.978 total

# switch to this patch

$ time (kubechn namespace)       
Context "context" modified.
Switched to namespace "namespace"
( kubechn namespace; )  0.21s user 0.06s system 39% cpu 0.714 total

This label should always exist in 1.22+ clusters. I expect relying on this would break kubechc for clusters older than that? Happy to make this fallback to the listing-all-namespaces way when the label check fails or something along those lines. Whatever sounds best to you.

Thanks again!

[aabouzaid]

@imbstack, thanks for your PR, that's a pretty good addition 🚀
since this feature is a bit new, I'd suggest making it disabled by default and enabling it by a flag (env var).

Later on, we can flip the flag and make it the default and keep the old style for anyone who works with older K8s versions.

[aabouzaid]

I will merge the PR once it has a flag (env var) to control the feature as mentioned.

[imbstack]

Ah yes sorry, I've been busy lately. I'll get a patch with that change before too long!

[imbstack]

Finally got around to this. I've tested this with the env var unset, and set to both listed values across the following cases:

1. namespace passed in and exists
2. namespace passed in and does not exist
3. no namespace passed in

I believe it works correctly in all of those cases. That said, I'm not a shell scripting expert so if there's a better way to go about any of this I'm happy to change whatever!

[imbstack]

I'll update README usage and such if this looks good!

[aabouzaid]

@imbstack Thanks for the change.
Apart from the typo, as shown in the CI pipeline, the current implementation is a bit complex.

You can simplify it by setting the default value the same way as here:
https://github.com/aabouzaid/kubech/blob/9f11a5486152de8ea13ef0fc1e269187ecaa7db5/kubech#L10

if you don't want to bother, I can do the whole change anyway.

[imbstack]

Ah, good call! Hopefully this is more what you're thinking of. If not, feel free to edit or drop the PR and make it yourself. Thanks again!

[aabouzaid]

@imbstack I've made a small fix and it's ready to merge.
Thanks for your contribution Brian 🙇