Improves external IP idempotency (#1493)

* Improves external IP idempotency

- Fixup in the external IP actions in the instance creation saga. We
  added nodes to create UUIDs for both external IPs and NICs, but only
  used them in the latter. This uses them in the external IP case too.
- Make the external IP allocation query idempotent and add test
  verifying that.

* Use inequality for DB record timestamps in tests

nexus/src/app/sagas/instance_create.rs

@@ -475,14 +475,14 @@ async fn sic_create_default_primary_network_interface(
 /// Create an external IP address for instance source NAT.
 async fn sic_allocate_instance_snat_ip(
     sagactx: ActionContext<SagaInstanceCreate>,
-) -> Result<Uuid, ActionError> {
+) -> Result<(), ActionError> {
     let osagactx = sagactx.user_data();
     let datastore = osagactx.datastore();
     let saga_params = sagactx.saga_params();
     let opctx =
         OpContext::for_saga_action(&sagactx, &saga_params.serialized_authn);
     let instance_id = sagactx.lookup::<Uuid>("instance_id")?;
-    let ip_id = Uuid::new_v4();
+    let ip_id = sagactx.lookup::<Uuid>("snat_ip_id")?;
     datastore
         .allocate_instance_snat_ip(
             &opctx,
@@ -492,7 +492,7 @@ async fn sic_allocate_instance_snat_ip(
         )
         .await
         .map_err(ActionError::action_failed)?;
-    Ok(ip_id)
+    Ok(())
 }
 
 /// Destroy an allocated SNAT IP address for the instance.
@@ -504,7 +504,7 @@ async fn sic_allocate_instance_snat_ip_undo(
     let saga_params = sagactx.saga_params();
     let opctx =
         OpContext::for_saga_action(&sagactx, &saga_params.serialized_authn);
-    let ip_id = sagactx.lookup::<Uuid>("snat_ip")?;
+    let ip_id = sagactx.lookup::<Uuid>("snat_ip_id")?;
     datastore
         .deallocate_instance_external_ip(&opctx, ip_id)
         .await
@@ -517,23 +517,28 @@ async fn sic_allocate_instance_snat_ip_undo(
 async fn sic_allocate_instance_external_ip(
     sagactx: ActionContext<SagaInstanceCreate>,
     ip_index: usize,
-) -> Result<Option<Uuid>, ActionError> {
+) -> Result<(), ActionError> {
     let osagactx = sagactx.user_data();
     let datastore = osagactx.datastore();
     let saga_params = sagactx.saga_params();
     let ip_params = saga_params.create_params.external_ips.get(ip_index);
     let ip_params = match ip_params {
         None => {
-            return Ok(None);
+            return Ok(());
         }
         Some(ref prs) => prs,
     };
     let opctx =
         OpContext::for_saga_action(&sagactx, &saga_params.serialized_authn);
     let instance_id = sagactx.lookup::<Uuid>("instance_id")?;
+    let name = format!("external_ip_id{ip_index}");
+    let ip_id = sagactx.lookup::<Option<Uuid>>(&name)?.ok_or_else(|| {
+        ActionError::action_failed(Error::internal_error(
+            "Expected a UUID for instance external IP",
+        ))
+    })?;
 
-    // Generate an ID and collect the possible pool name for this IP address
-    let ip_id = Uuid::new_v4();
+    // Collect the possible pool name for this IP address
     let pool_name = match ip_params {
         params::ExternalIpCreate::Ephemeral { ref pool_name } => {
             pool_name.as_ref().map(|name| db::model::Name(name.clone()))
@@ -549,7 +554,7 @@ async fn sic_allocate_instance_external_ip(
         )
         .await
         .map_err(ActionError::action_failed)?;
-    Ok(Some(ip_id))
+    Ok(())
 }
 
 async fn sic_allocate_instance_external_ip_undo(
@@ -559,16 +564,23 @@ async fn sic_allocate_instance_external_ip_undo(
     let osagactx = sagactx.user_data();
     let datastore = osagactx.datastore();
     let saga_params = sagactx.saga_params();
+    if ip_index >= saga_params.create_params.external_ips.len() {
+        return Ok(());
+    }
+
     let opctx =
         OpContext::for_saga_action(&sagactx, &saga_params.serialized_authn);
-    let name = format!("external_ip{ip_index}");
-    let maybe_ip_id = sagactx.lookup::<Option<Uuid>>(name.as_str())?;
-    if let Some(ip_id) = maybe_ip_id {
-        datastore
-            .deallocate_instance_external_ip(&opctx, ip_id)
-            .await
-            .map_err(ActionError::action_failed)?;
-    }
+    let name = format!("external_ip_id{ip_index}");
+    let ip_id =
+        sagactx.lookup::<Option<Uuid>>(name.as_str())?.ok_or_else(|| {
+            ActionError::action_failed(Error::internal_error(
+                "Expected a UUID for instance external IP",
+            ))
+        })?;
+    datastore
+        .deallocate_instance_external_ip(&opctx, ip_id)
+        .await
+        .map_err(ActionError::action_failed)?;
     Ok(())
 }