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.