feat: Add use plugin cache flag

[wolmi]

what

Add flag to control the usage of plugin cache

why

By using atlantis for a long time we found a posible race condition where multiple projects in the same repository in different folders detects a change in a common module that is used by all the projects.

An example of folder structure is:

├── google
│   ├── environments
│   │   ├── prod
│   │   ├── staging
│   │   ├── dev
│   │   ├── modules
└── atlantis.yaml

Any time a change is made to a module used by the 3 environments a plan needs to run but all the times one ore none of them can run the plan properly becouse the next error:

╷
│ Error: Required plugins are not installed
│ 
│ The installed provider plugins are not consistent with the packages
│ selected in the dependency lock file:
│   - registry.terraform.io/hashicorp/google: the cached package for registry.terraform.io/hashicorp/google 4.80.0 (in .terraform/providers) does not match any of the checksums recorded in the dependency lock file
│ 
│ Terraform uses external plugins to integrate with a variety of different
│ infrastructure services. You must install the required plugins before
│ running Terraform operations.
╵

The package that changes id different on each run that means that seems to be a race condition.

tests

references

#3547

hashicorp/terraform#31964
hashicorp/terraform#33479

[GenPage]

Can you add documentation to the site for this?

[wolmi]

I've added the flag to the server-configuration section.

[jamengual]

you can add something on one of these sections: https://github.com/runatlantis/atlantis/tree/main/runatlantis.io/docs or you can add an explanation of why is needed with an example in the server-configuration page where you added the flag.

…

On Mon, Sep 4, 2023 at 12:21 AM wolmi ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In runatlantis.io/docs/server-configuration.md <#3720 (comment)> : > +### `--use-tf-plugin-cache` +```bash +atlantis server --use-tf-plugin-cache=false +# or +ATLANTIS_USE_TF_PLUGIN_CACHE=false +``` +Set it to false if you want to disable terraform plugin cache + Ok, because is my first PR I was not sure how to add the documentation. It's ok to add a new page? or do you think this can be added in an existing page? — Reply to this email directly, view it on GitHub <#3720 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAQ3ERCDWYUQEEO2F6YEKVTXYV6RPANCNFSM6AAAAAA4FTBN3Q> . You are receiving this because your review was requested.Message ID: ***@***.***>

[X-Guardian]

I would also mention in the docs that this is a known Terraform issue, not an Atlantis one. Discussion here: hashicorp/terraform#31964 and possible PR to improve the situation here: hashicorp/terraform#33479.

[GenPage]

LGTM when tests are green, thank you @X-Guardian for the review as well

[jamengual]

@wolmi can you check the tests?

[wolmi]

I've changed the version to pass the test, is anything more need to merge this?

[jamengual]

thanks @wolmi for your contribution

[virgofx]

Is there any way this sentence could be made more clear?

Specifically, does disabling or enabling of this flag prevent the race condition that's noted in the corresponding bug report?

E.g - one has Atlantis with lots of parallel plans and applies. This flag is "useful" but how? Should it be set to false? If so, the wording should dictate that