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Moved block

As explained in Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu

A moved block is a Terraform configuration block that declares a change in the address or location of a managed resource so Terraform can preserve its existing state.

Suppose you rename a Terraform resource or move it into a child module. Its configuration now has a new address, but its existing state still uses the old one. Without a migration, Terraform can plan to destroy the old resource and create a replacement. A `moved` block tells Terraform to associate that existing resource with its new address instead. section 6.5.2

Listing 6.15 moved and removed blocks and resources
resource "random_password" "main" {           #1
  length = 12
}
 
moved {                                       #2
  from = random_password.my_password          #3
  to   = random_password.main                 #4
}
 
removed {
  from = aws_s3_bucket.bucket                 #5
 
  lifecycle {                                 #6
    destroy = false                           #7
  }
}

For a rename, set `from` to the address already in state and `to` to the address of the renamed resource in the configuration. The listing moves `random_password.my_password` to `random_password.main`. section 6.5.2

Listing 6.16 moved block and modules
module "password" {                           #1
  source = "./modules/password"
}
 
moved {                                       #2
  from = random_password.my_password          #3
  to   = module.password.random_password.main #4
}

The destination can also be inside a child module. Here, the existing password resource moves from the root module to `module.password.random_password.main`. section 6.5.2

Terraform processes a move only while the `from` address exists in state. After migration, the block does nothing; in a new environment with no old resource, Terraform can create the configured destination normally. Keep moved blocks in shared modules so users upgrading from older versions can still migrate without an unexpected replacement. Unlike an `import` block, a moved block relocates an address within one Terraform project rather than bringing an external resource under management. section 6.5.2 section 9.5.4 section 2.9

How Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu covers it

How deep it goes
Defines `from` and `to`, explains when migration occurs, and demonstrates resource and module moves without detailing command-level execution.
Examples
Uses a password-resource rename and a move from the root module into a child module.
What it assumes
Introduces address migration through existing resource and module configurations, but does not teach Terraform project setup.
What you can do after
Operate/configure it to migrate resource addresses across environments without forcing replacement during a rename or module extraction.
How it connects
Connects Terraform state and module refactoring with the contrasting import and removed blocks.
Cover of Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu
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This explainer was generated by Manning's knowledge graph from the text of Terraform in Depth: Infrastructure as Code with Terraform and OpenTofu. The section links point to the parts of the book it draws on.