Add ERB template support to the command helpers

[gwvandesteeg]

Summary

Add the ability to do ERB template resolution on the fields (in particular the args field) passed to the command definition in the config/args/terraform.rb file.

Motivation

I'm hoping to be able to generate suitable output Terraform plan files when using terraspace all plan with an individual plan name for each stack/instance to review the changes and to feed the suitable plans in to the apply/up commands.

Guide-level explanation

In particular i'd be interested in doing the below so that I can add the "plan" files to my MR/PR's via the CI/CD process (GitLab).

command("plan",
  args: ["-lock-timeout=22m", '-out=<%= expansion(":ENV-:ACCOUNT-:REGION-:MOD_NAME-:INSTANCE") %>.tfplan.json'],
)

[tongueroo]

Args files are just ruby, so it wouldn't be ERB. Instead, it would be something like this:

config/args/terraform.rb

command("plan",
  args: ["-lock-timeout=22m", "-out=#{expansion(":ENV-:ACCOUNT-:REGION-:MOD_NAME-:INSTANCE")}.tfplan.json"],
)

Unfortunately, it's not simple as including the helper methods to the args builder. The reason is that helpers are currently designed for tfvars file where the dependency graph is calculated. Terraspace actually evaluates the tfvars files twice and caches the calculated results of the helpers methods for performance reasons. The dependency graph processing logic would needed to be altered so the first pass would not be a regular ruby eval but possibly a parser. This avoids the the helpers actually being invoked in the first pass. Then helpers would be more easily be included elsewhere. Think the original reason took the ruby eval twice approach was because it's faster than writing a decent parser.

So it's a bit complex right now 🧐 Will take a decent amount of time. Will consider PRs. Of course no sweat either way 👍

[gwvandesteeg]

The main reason is that i'm trying to get hold of an uniquely named plan file for each stack being spun up when using terraspace all plan, I've got a project with 13 stacks and growing that i'd like to get artefacts for during the plan stage to validate and integrate with my CI/CD platform (GitLab.com).

[tongueroo]

Thinking will add an option to handle plans. Perhaps:

terraspace all plan --outs

Maybe the default conventional saves the plan to an expanded path. But you can also provide specify pattern the command

terraspace all plan --outs ":ENV-:ACCOUNT-:REGION-:MOD_NAME-:INSTANCE"

Unsure when will get to this, probably not for a while. Would like to provide this ability though. Happy to consider PRs. No sweat either way of course. 👍 Thanks!

[gwvandesteeg]

That'd work fine, as long as each plan output file has a unique name and/or path it'll be workable.

[tongueroo]

Closed in favor of #156