fix: do not re-render the default backend in haproxy-route-tcp

docs/changelog.md

@@ -8,6 +8,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 
 Each revision is versioned by the date of the revision.
 
+## 2026-04-21
+
+- Do not render the default backend if there are no other backends in in the haproxy-route-tcp.
+
 ## 2026-04-17
 
 - Added missing settings from haproxy-route-tcp relation template.

docs/release-notes/artifacts/pr0476.yaml

@@ -0,0 +1,14 @@
+version_schema: 2
+changes:
+  - title: Do not render the default backend if there are no other backends
+    author: skatsaounis
+    type: bugfix
+    description: >
+      Do not render the default backend if there are no other backends in the
+      haproxy-route-tcp relation template, to avoid rendering unused
+      configuration.
+    urls:
+      pr:
+        - https://github.com/canonical/haproxy-operator/pull/476
+    visibility: public
+    highlight: false

haproxy-operator/templates/haproxy_route_tcp.cfg.j2

@@ -95,8 +95,8 @@ backend {{ frontend.default_backend_name }}
 {% endfor %}
 {% endif %}
 
-{# Render each backend for the frontend. #}
-{% for backend in frontend.backends %}
+{# Render each backend for the frontend. Skip rendering if there's only the default backend. #}
+{% for backend in frontend.backends if frontend.backends|length > 1 %}
 backend {{ backend.name }}
     mode tcp
 {% if backend.application_data.load_balancing %}

haproxy-operator/tests/integration/test_haproxy_route_tcp.py

@@ -97,3 +97,18 @@ def test_haproxy_route_tcp(
             "timeout queue 2s",
         ]
     )
+
+    assert all(
+        entry in haproxy_config
+        for entry in [
+            "backend haproxy_route_tcp_4444_default_backend",
+            "default_backend haproxy_route_tcp_4444_default_backend",
+        ]
+    )
+    assert all(
+        entry not in haproxy_config
+        for entry in [
+            f"{any_charm_haproxy_route_tcp_requirer}_4444",
+            f"default_backend {any_charm_haproxy_route_tcp_requirer}_4444",
+        ]
+    )