Ability to manually specify charts to check

[gabegorelick]

Is your feature request related to a problem? Please describe.

Nova does two things according to the README:

Nova scans your cluster for installed Helm charts, then cross-checks them against all known Helm repositories

I'd like to be able to use Nova for that second part (cross-checking Helm charts against their repositories to see if they're outdated and/or deprecated) without the first part (discovering the charts by scanning a cluster).

For example, scanning may fail if you didn't use helm install to install a chart (see #6). Or you may want to see if a chart is deprecated before you install it.

Describe the solution you'd like
Ability to manually specify the set of charts to check. Something like a --charts CLI option. Specifying this option would disable scanning for charts in the cluster and instead check the specified charts.

Describe alternatives you've considered
If you don't want scanning for charts, then perhaps there is a more purpose built tool that would make sense to use instead of Nova?

[RohitKochhar]

I'll tackle this. @rbren if you can assign this issue to me that would be perfecto

[RohitKochhar]

I am almost thinking this would be better as a different sub-command something like nova precheck

There are a few reasons I am thinking this:

1. nova find implies that we want to scan the cluster, so it seems a bit unintuitive to "ask" nova to find charts that aren't in the cluster, instead it would make more sense to "ask" nova to precheck a chart before install.
2. For the amount of logic it would take to add this as a part of find, it would make more sense to just create a new subcommand. Having any sort of logic within find that would enable/disable scanning the cluster may overcomplicate things.

cc: @rbren @sudermanjr let me know what you guys think on this

[sudermanjr]

I like the idea of making this a separate sub-command. I don't particularly love the name precheck. Either a name that encompasses the functionality better, or even a flag that modifies the behavior or find, such as --only-check=[]string might work.

[RohitKochhar]

My concern with using it as a flag would be that the current logic flow of scanning the cluster would be bypassed, and that adding a conditional branch to see if that flag is handed to the find command would be equivalent to a separate command altogether (not sure if that makes sense, just don't want to mess around with the find logic if we aren't scanning the cluster)

I also am a bit curious about the use case here... so either the chart is installed not using helm and we want to check if it's outdated, or check if it's outdated before installing? I don't understand a scenario in which the chart is out of date before it's installed

@sudermanjr