Terraform does not run configuration files from top to bottom. It builds a dependency graph from references. Execution order emerges from that graph.
The depends_on meta-argument does not move data. It does not validate logic. It inserts an explicit ordering edge when a real dependency cannot be expressed through a reference.
This distinction matters when external systems treat timing as meaning. A “ready” flag stored in SSM can trigger another pipeline even if the underlying infrastructure is not finished. Without an explicit edge, Terraform may run resources in parallel.
This lesson focuses on:
- Implicit dependencies created through references
- Why file order is irrelevant
- When side effects require explicit ordering
- How data source reads can occur too early
- Why overusing
depends_onreduces graph parallelism
The core model is simple: references encode identity and order. depends_on encodes timing only.