VAIDATION ANMD PRE AND POST CONDITION KINDA SIMILIAR BUT ACTUALLY NOT

Before plan — Terraform hasn't even started thinking about what to create/change. It just reads your variable value and immediately checks it. No AWS calls, no state file reading, nothing.

you run terraform plan
     ↓
Terraform reads variables        ← validation runs HERE
     ↓
Terraform reads state + AWS
     ↓
Terraform figures out what to create/change   ← this is "the plan"

During plan — Terraform has already read everything (state file, current AWS resources, all variables). Now it's building the plan and checks precondition at this point — so it has full context of everything.

Terraform reads state + AWS
     ↓
Terraform figures out what to create/change
     ↓
precondition runs HERE — checks before actually doing anything

So the real difference in timing:

• Validation → runs the moment Terraform sees the variable — knows nothing else yet
• Precondition → runs after Terraform has full picture — can reference anything