Add explanation comment for socket.gethostname

localstack · simonrw · Mar 20, 2023 · Feb 23, 2023 · Feb 27, 2023 · Feb 27, 2023
commit 53dab3ac64b4a0102e7154d3477fa176276a3701
diff --git a/localstack/testing/pytest/fixtures.py b/localstack/testing/pytest/fixtures.py
@@ -1984,6 +1984,18 @@ def factory(**kwargs):
 @pytest.fixture
 def assert_host_customisation(monkeypatch):
     hostname_external = f"external-host-{short_uid()}"
+    # `LOCALSTACK_HOSTNAME` is really an internal variable that has been
+    # exposed to the user at some point in the past. It is used by some
+    # services that start resources (e.g. OpenSearch) to determine if the
+    # service has been started correctly (i.e. a health check). This means that
+    # the value must be resolvable by LocalStack or else the service resources
+    # won't start properly.
+    #
+    # One hostname that's always resolvable is the hostname of the process
+    # running LocalStack, so use that here.
+    #
+    # Note: We cannot use `localhost` since we explicitly check that the URL
+    # passed in does not contain `localhost`, unless it is requried to.
     localstack_hostname = socket.gethostname()
     monkeypatch.setattr(config, "HOSTNAME_EXTERNAL", hostname_external)
     monkeypatch.setattr(config, "LOCALSTACK_HOSTNAME", localstack_hostname)