add note about idempotency in ims_create_vlans and ims_remove_vlans

README.md

@@ -894,6 +894,15 @@ subscriptions against the OSS and BSS. The decorators
 and the `@step` decorator is used to define workflow steps that can be
 used in any type of workflow.
 
+### Workflow step idempotence
+
+It is good practice to define [idempotent](https://en.wikipedia.org/wiki/Idempotence) steps; a step may have to be 
+retried after failing partway through its execution.
+Be aware that some example steps for L2VPN are not idempotent (yet): 
+- `ims_create_vlans` in `/workflows/l2vpn/create_l2vpn.py`
+- `ims_remove_vlans` in `/workflows/l2vpn/terminate_l2vpn.py`
+If you want to use these workflows, the above steps should be refactored to make them idempotent.
+
 ### Workflow Architecture - Passing information from one step to the next
 
 Information between workflow steps is passed using `State`, which is

workflows/l2vpn/create_l2vpn.py

@@ -118,6 +118,9 @@ def to_sap(port: UUIDstr) -> SAPBlockInactive:
 
 @step("Create VLANs in IMS")
 def ims_create_vlans(subscription: L2vpnProvisioning) -> State:
+    """Note: this step is not idempotent.
+    If you want to use this workflow, this step has to be
+    refactored to make it idempotent."""
     saps = subscription.virtual_circuit.saps
 
     sap_payloads = create_saps_in_netbox(saps, subscription)

workflows/l2vpn/terminate_l2vpn.py

@@ -40,6 +40,9 @@ def ims_remove_l2vpn(subscription: L2vpn) -> None:
 
 @step("Remove VLANs from IMS")
 def ims_remove_vlans(subscription: L2vpn) -> None:
+    """Note: this step is not idempotent.
+    If you want to use this workflow, this step has to be
+    refactored to make it idempotent."""
     saps = subscription.virtual_circuit.saps
 
     remove_saps_in_netbox(saps)