apply-all should error if TERRAGRUNT_SOURCE is specified

[yinzara]

I caused a MAJOR production outage across a set of tenants because I accidentally had the TERRAGRUNT_SOURCE environment variable set when I performed an "apply-all" across our tenants. This caused more than 800 resources across 6 customers to be deleted because TG attempt to apply the source from TERRAGRUNT_SOURCE against a set of terragrunt.hcl files that were for different modules.

TERRAGRUNT_SOURCE is incompatible with apply-all unless all modules being applied are for the same source. apply-all should have prevented this from happening either by erroring or prompting me to confirm specifically about TERRAGRUNT_SOURCE.

[brikis98]

Sorry to hear you hit this issue. That sounds really painful 😕

FWIW, we use TERRAGRUNT_SOURCE quite regularly with apply-all, especially when spinning up totally new environments. That said, there are a number of limitations / gotchas with TERRAGRUNT_SOURCE, and we've captured a proposal for a better replacement in #1138. Let's continue the discussion in there. I'll close this issue for now.