Overview
Terraform and Ansible are both infrastructure-as-code tools but solve different problems: Terraform declaratively provisions and tracks cloud infrastructure using a state file, while Ansible procedurally configures and manages software on existing hosts with no persistent state. Many teams use them together — Terraform to stand up infrastructure, Ansible to configure it.
Comparison Diagram
Comparison Table
| Aspect | Terraform | Ansible |
|---|---|---|
| Primary purpose | Provision and tear down cloud/infra resources (VMs, networks, DBs) | Configure software and manage state on existing hosts |
| Configuration language | HCL (HashiCorp Configuration Language), declarative | YAML playbooks, procedural task lists |
| Execution model | Builds a dependency graph and applies changes in parallel where possible | Executes tasks sequentially, in order, per host |
| State management | Maintains a state file mapping config to real resources | Stateless — queries live system facts on each run |
| Idempotency approach | Diffs desired config against state file before acting | Each module checks current condition before making a change |
| Connectivity/agent requirement | Agentless — calls cloud/provider APIs directly | Agentless — connects over SSH or WinRM to target hosts |
| Failure & recovery handling | Partial applies are resolved by re-running against the state file | Reruns the playbook from the start; tasks are re-checked, not resumed |
Key Differences
- Terraform tracks infrastructure in a persistent state file; Ansible has no state store and reads live system facts each run.
- Terraform resolves a dependency graph to apply changes in parallel; Ansible runs tasks sequentially.
- Terraform talks to infrastructure through provider APIs; Ansible connects to hosts via SSH/WinRM.
- Terraform is built for provisioning infra; Ansible is built for configuration of what already exists.
- They’re commonly paired: Terraform creates the servers, then Ansible configures them.
When to Use Each
Terraform
- Provisioning Cloud Infrastructure: Creating and tearing down VMs, networks, and managed services is exactly the resource-lifecycle problem Terraform’s provider APIs and dependency graph are built for.
- Needing a Source of Truth for What Exists: The state file gives you a queryable record of every resource under management, which Ansible’s stateless model doesn’t provide.
- Parallel, Dependency-Aware Rollouts: When resources depend on each other, Terraform’s graph-based apply creates them in the right order automatically, in parallel where safe.
Ansible
- Configuring Software on Existing Hosts: Installing packages, writing config files, and starting services on servers that already exist is Ansible’s core job, with no infrastructure to provision.
- Orchestrating Multi-Server Deployment Steps: Sequential, ordered task execution across many hosts over SSH suits rollout playbooks better than a declarative state diff.
- Agentless Configuration Without Persistent State: When you don’t want to manage a state file and prefer each run to check live system facts directly, Ansible’s stateless design fits.