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Dependencies and Graph

Updated Jan 24, 2021 ·

Overview​

Terraform builds a dependency graph from resource references. It uses that graph to decide which resources can be created in parallel and which resources must wait.

Implicit Dependencies​

An implicit dependency is created when one resource references another resource.

resource "aws_dynamodb_table_item" "item" {
  table_name = aws_dynamodb_table.table.name
}

Terraform knows the table must exist before the table item can be created.

Dependency Problems​

A dependency problem often appears when a resource uses a literal string instead of a reference.

resource "aws_dynamodb_table_item" "item" {
  table_name = "lab08-ddb-table"
}

The value may look correct, but Terraform cannot infer that this item depends on a Terraform-managed table unless the resource is referenced.

Visualize the Graph​

Terraform can print the dependency graph in DOT format.

terraform graph
terraform graph | dot -Tpng > graph.png

Note: The graph is most useful when troubleshooting ordering issues, module relationships, or unexpected replacement behavior.