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Terraform Command apply refershonly

Step-01: Introduction

Understand terraform refresh in detail

  • This commands comes under Terraform Inspecting State
  • Understanding terraform apply -refresh-only clears a lot of doubts in our mind and terraform state file and state feature
  • The terraform apply -refresh-onlycommand is used to reconcile the state Terraform knows about (via its state file) with the real-world infrastructure.
  • This can be used to detect any drift from the last-known state, and to update the state file.
  • This does not modify infrastructure, but does modify the state file. If the state is changed, this may cause changes to occur during the next plan or apply.
  • terraform apply -refresh-only: Update terraform.tfstate state file against real resources in cloud
  • Desired State: Local Terraform Manifest (All *.tf files)
  • Current State: Real Resources present in your cloud

Step-02: Review Terraform Configs

  • c1-versions.tf
  • c2-resource-group.tf

Step-03: Execute Terraform Commands

# Terraform Initialize
terraform init

# Terraform Validate
terraform validate

# Terraform Plan
terraform plan

# Terraform Apply
terraform apply -auto-approve

Step-04: Add a new tag to Resource using Azure Management Console

"tag3" = "my-tag-3"

Step-05: Execute terraform plan

  • You should observe no changes to state file because plan does the comparison in memory
  • Verify terraform.tfstate file and it should not have any changes
  • But it show the differences of tags.
# Execute Terraform plan
terraform plan 

# Verify Terraform State File (recent timestamp)
ls -lrta 

# Review Terraform State file using terraform show command
terraform show

Step-06: Execute terraform apply -refresh-only

  • You should see terraform state file updated with new demo tag
# Execute terraform plan -refresh-only
terraform plan -refresh-only

# Execute terraform apply -refresh-only
terraform apply -refresh-only

# Review terraform state file
1) terraform show
2) A new tag will be added to Azure Resource Group 
"tag3" = "my-tag-3"

Step-07: Update TF Configs

  • Now you have manual changes done on Azure Portal in your state file so that you can track that change via Terraform.
  • You also need to update your TF Configs (desired state) with that change so that, this new tag change "tag3" = "my-tag-3" can be officially managed by Terraform
  • c2-resource-group.tf: Add Tag3 referencing the state file.
  • Simply uncomment tag3
# Run Terraform Plan
terraform plan
Observation: 
1. Tag3 change present in Current State (Real Cloud Env on Azure Portal) and in Terraform State file but not present in TF Configs (desired state)
2. So `terraform plan` will say we need to get rid of that change in next `terraform apply`
3. Now add that `tag3` in c2-resource-group.tf

# Resource-1: Azure Resource Group
resource "azurerm_resource_group" "myrg" {
  name = "myrg1"
  location = "eastus"
  tags = {
    "tag1" = "my-tag-1"
    "tag2" = "my-tag-2"
    "tag3" = "my-tag-3"
  }
}

# Run Terraform Plan
terraform plan
Observation:
1. No changes to infrastructure
TF Configs (Desired State) - Good
TF State File - Good
Azure Portal (Current State) - Good

Step-08: Clean-Up

# Destroy Resources
terraform destroy -auto-approve

# Delete files
rm -rf .terraform*
rm -rf terraform.tfstate*