Fix grand-central hostname corruption when cluster name recurs in external DNS

CHANGES.rst

@@ -5,6 +5,9 @@ Changelog
 Unreleased
 ----------
 
+* Fixed the grand-central hostname being corrupted when the cluster name recurs
+  later in its external DNS name.
+
 2.63.0 (2026-08-12)
 -------------------
 

crate/operator/grand_central.py

@@ -766,6 +766,20 @@ def grand_central_uses_traefik(spec: kopf.Spec) -> bool:
     return get_grand_central_exposure(spec) == "traefik"
 
 
+def _grand_central_hostname(cluster_name: str, external_dns: str) -> str:
+    """
+    Derive the grand-central hostname from a cluster's external DNS name.
+
+    ``external_dns`` is built as ``<cluster_name>.<region>.<domain>.`` so the
+    cluster name is always its leading label. The grand-central hostname is the
+    same name with a ``.gc`` label inserted after that leading label.
+
+    :param cluster_name: The CrateDB cluster name (the leading DNS label).
+    :param external_dns: The cluster's external DNS name (may have a trailing dot).
+    """
+    return external_dns.replace(cluster_name, f"{cluster_name}.gc", 1).rstrip(".")
+
+
 async def create_grand_central_exposure(
     namespace: str,
     name: str,
@@ -794,7 +808,7 @@ async def create_grand_central_exposure(
     owner_references = get_owner_references(name, meta)
     cluster_name = spec["cluster"]["name"]
     external_dns = spec["cluster"]["externalDNS"]
-    hostname = external_dns.replace(cluster_name, f"{cluster_name}.gc").rstrip(".")
+    hostname = _grand_central_hostname(cluster_name, external_dns)
     labels = get_grand_central_labels(name, meta)
     cidrs = spec["cluster"].get("allowedCIDRs", None)
 

tests/test_grand_central_exposure.py

@@ -22,6 +22,7 @@
 import pytest
 
 from crate.operator.grand_central import (
+    _grand_central_hostname,
     get_grand_central_exposure,
     grand_central_uses_traefik,
 )
@@ -70,3 +71,38 @@ def test_explicit_grand_central_exposure_wins_over_cluster():
 def test_grand_central_exposure_falls_back_to_cluster():
     spec = {"cluster": {"exposure": "traefik"}}
     assert get_grand_central_exposure(spec) == "traefik"
+
+
+@pytest.mark.parametrize(
+    "cluster_name, external_dns, expected",
+    [
+        # Non-colliding: cluster name appears only as the leading label.
+        (
+            "mycluster",
+            "mycluster.eks1.us-west-2.aws.cratedb.net.",
+            "mycluster.gc.eks1.us-west-2.aws.cratedb.net",
+        ),
+        # Collision with the region: 'us-west' also occurs in 'us-west-2'.
+        (
+            "us-west",
+            "us-west.eks1.us-west-2.aws.cratedb.net.",
+            "us-west.gc.eks1.us-west-2.aws.cratedb.net",
+        ),
+        # Collision with the cloud suffix: 'aws' also occurs in '.aws.'.
+        (
+            "aws",
+            "aws.eks1.us-west-2.aws.cratedb.net.",
+            "aws.gc.eks1.us-west-2.aws.cratedb.net",
+        ),
+        # Cluster literally named 'gc'.
+        (
+            "gc",
+            "gc.eks1.eu-central-1.azure.cratedb.net.",
+            "gc.gc.eks1.eu-central-1.azure.cratedb.net",
+        ),
+    ],
+)
+def test_grand_central_hostname_only_replaces_leading_label(
+    cluster_name, external_dns, expected
+):
+    assert _grand_central_hostname(cluster_name, external_dns) == expected