fix(oracle): fix subnet selection logic

When a subnet is not associated with an availability domain (AD),
we should not ignore the subnet just because it does not match our
configured AD. This change fixes the subnet selection logic to first
check if the subnet is associated with an AD before checking if it
matches the configured AD.

Before this change, the subnet selection logic was flawed and would
say it was using a certain subnet, but due to this bad AD logic, it
would actually not actually use the subnet it said it was using.

pycloudlib/oci/utils.py

@@ -89,23 +89,33 @@ def get_subnet_id(
         if len(vcns) > 1:
             raise PycloudlibError(f"Found multiple vcns with name: {vcn_name}")
         vcn_id = vcns[0].id
+        chosen_vcn_name = vcns[0].display_name
     else:  # if no vcn_name specified, use most recently created vcn
-        vcn_id = network_client.list_vcns(compartment_id, retry_strategy=retry_strategy).data[0].id
+        vcns = network_client.list_vcns(compartment_id, retry_strategy=retry_strategy).data
+        if len(vcns) == 0:
+            raise PycloudlibError("No VCNs found in compartment")
+        vcn_id = vcns[0].id
+        chosen_vcn_name = vcns[0].display_name
+
 
     subnets = network_client.list_subnets(
         compartment_id, vcn_id=vcn_id, retry_strategy=retry_strategy
     ).data
     subnet_id = None
     for subnet in subnets:
         if subnet.prohibit_internet_ingress:  # skip subnet if it's private
-            log.debug("Ignoring private subnet: %s", subnet.id)
+            log.debug("Ignoring private subnet: %s [id: %s]", subnet.display_name, subnet.id,)
+            continue
+        if subnet.availability_domain and subnet.availability_domain != availability_domain:
+            log.debug(
+                "Ignoring public subnet in different availability domain: %s [id: %s]",
+                subnet.display_name,
+                subnet.id,
+            )
             continue
-        log.debug("Using public subnet: %s", subnet.id)
-        if subnet.availability_domain == availability_domain:
-            subnet_id = subnet.id
-            break
-    else:
-        subnet_id = subnets[0].id
+        log.info("Using public subnet: %s [id: %s]", subnet.display_name, subnet.id)
+        subnet_id = subnet.id
+        break
     if not subnet_id:
-        raise PycloudlibError(f"Unable to determine subnet id for domain: {availability_domain}")
+        raise PycloudlibError(f"Unable to find suitable subnet in VCN {chosen_vcn_name}")
     return subnet_id