LoC Digital Garden

How can I think about Terraform?

Terraform is declarative not imperative. It describes an end state. It does not instruct how something should be run.

How does Terraform 'read' the code?

Terraform does not read from 'top to bottom', rather Terraform has a birds eye view: it reads the entire file, looks at all the interdependencies.

How does terraform 'know' there are changes?

Terraform will check three things:

1. Files (e.g. has main.tf) changed?
2. State file (managed by Terraform )
3. Does it match up with reality? i.e. do I actually have the resources stated in the file?

Data sources

Think of a data source as 'read only'. This is a read only source of data.

Resource blocks

These are created and managed. Think of resource blocks as being similar to 'CRUD' operations. Unlike a data source a resource block can update and delete things. You can't have the same resource described more than once.

Locals

Internal state not visible to the outside. Scoped to the module.

Module

A folder containing a bunch of terraform files. You can create an instance of the module.

Outputs

Go from inside of the module to the outside.

Vars

Can be access from outside of the module into the module.

Inputs

Are like arguments.