Lesson 4 of 4 ยท Resource Relationships & Dependencies

Debugging dependency cycles

A dependency cycle occurs when Terraform cannot decide what to create first because resources depend on each other. The fix is usually architectural: separate creation from configuration, or reference a value available earlier in the lifecycle.

Example

# app1 reads app2.private_ip
# app2 reads app1.private_ip
# Terraform cannot create either resource first.

Step by step

  1. Read every resource named in the cycle.
  2. Find the pair of references that loop.
  3. Move one relationship to a later configuration step if appropriate.
  4. Validate the revised graph.

Common mistakes to avoid

  • Trying to force a cycle with declaration order.
  • Ignoring a cycle because both resources look valid individually.