Asserting number of changes

[smailc]

Please could you tell me how we check for no changes after our Terraform apply? I want to be able to check the difference between two module versions and I need to know that there are no changes.

Plan: 0 to add, 0 to change, 0 to destroy.

Also if there is a solution how can it be done using Terragrunt? i.e. how can we test that module x has 1 add but module y should have 2 change and 1 destroy?

Thanks

[ludoo]

For apply we do not have the JSON output that Terraform optionally provides for plan, so your introspection capabilities into what Terraform actually did are a lot more limited: what you can do is get the return from the apply call, and parse the text output to figure out if the two differ.

If you just need to spot changes using the difflib module on the two apply outputs might be what you want. If you need to compare against expected results, I'm afraid you'll have to implement your own solution via regular expressionss.

For Terragrunt, we do have support here but it's not something I ever used as I don't use Terragrunt (we can get into a philosophical discussion on the why if you want). The code supporting Terragrunt here was mostly contributed, so I can't be of much help.

[smailc]

Thanks @ludoo - I have done something close to what I want to achieve by checking the plan for instances of no changes on second run:

substring = "Apply complete! Resources: 0 added, 0 changed, 0 destroyed."
no_changes = [i for i in range(len(tg_plan)) if tg_plan.startswith(substring, i)]
assert len(no_changes) == 6, "\nUnexpected number of Terraform changes in apply. Expecting six modules to show no changes. Failed test\n"```

[ludoo]

Ah well, if you use plan instead of apply you can get a full plan object containing all resources and the underlying raw JSON plan. That would allow you to count differences even across resource types, and check what actually changed.

[smailc]

Ok thanks. I'll perhaps use that as well. I like to apply in test because plans don't always succeed on apply.