test: cover DNS entrypoint discovery

tests/integration/test_live_nodes.py

@@ -2,10 +2,15 @@
 
 from __future__ import annotations
 
+from collections.abc import Sequence
+from urllib.parse import urlsplit
+
 import pytest
 
 from alternator import AlternatorConfigBuilder, Auth, Helper, KeyRouteAffinityMode
+from alternator._http import create_sync_http_fetcher
 from alternator.async_client import AsyncHelper
+from tests.conftest import FakeAlternatorServer
 from tests.integration import SCYLLA_HOST, SCYLLA_PORT, SKIP_INTEGRATION
 
 pytestmark = [
@@ -27,6 +32,19 @@ def _affinity_config() -> object:
     )
 
 
+def _live_cluster_localnodes() -> Sequence[str]:
+    fetcher = create_sync_http_fetcher(timeout_seconds=5.0)
+    return fetcher(f"http://{SCYLLA_HOST}:{SCYLLA_PORT}/localnodes")
+
+
+def _dns_entrypoint_config(fake_url: str) -> object:
+    parsed = urlsplit(fake_url)
+    assert parsed.port is not None
+    return (
+        AlternatorConfigBuilder().with_seeds("localhost").with_port(parsed.port).build()
+    )
+
+
 class TestLiveNodeHelperDiagnostics:
     """Verify sync helper diagnostics and shared-client lifecycle."""
 
@@ -49,6 +67,19 @@ def test_helper_exposes_nodes_clients_and_partition_keys(self) -> None:
             resource = helper.resource()
             assert "TableNames" in resource.meta.client.list_tables()
 
+    def test_helper_discovers_live_cluster_nodes_from_dns_entrypoint(
+        self,
+        fake_alternator_server: FakeAlternatorServer,
+    ) -> None:
+        fake_alternator_server.set_localnodes(_live_cluster_localnodes())
+
+        with Helper(
+            _dns_entrypoint_config(fake_alternator_server.url("/")),
+            auth=Auth.disabled(),
+        ) as helper:
+            assert helper.update_live_nodes()
+            assert helper.get_nodes()
+
 
 class TestAsyncLiveNodeHelperDiagnostics:
     """Verify async helper diagnostics and shared-client lifecycle."""
@@ -73,3 +104,17 @@ async def test_helper_exposes_nodes_clients_and_partition_keys(self) -> None:
 
             client = await helper.client()
             assert "TableNames" in await client.list_tables()
+
+    @pytest.mark.asyncio
+    async def test_helper_discovers_live_cluster_nodes_from_dns_entrypoint(
+        self,
+        fake_alternator_server: FakeAlternatorServer,
+    ) -> None:
+        fake_alternator_server.set_localnodes(_live_cluster_localnodes())
+
+        async with AsyncHelper(
+            _dns_entrypoint_config(fake_alternator_server.url("/")),
+            auth=Auth.disabled(),
+        ) as helper:
+            assert await helper.update_live_nodes()
+            assert helper.get_nodes()

tests/unit/test_sync_manager.py

@@ -2,13 +2,16 @@
 
 import time
 from collections.abc import Sequence
+from urllib.parse import urlsplit
 
 import pytest
 
+from alternator._http import create_sync_http_fetcher
 from alternator.config import Config
 from alternator.core.live_nodes import NoNodesAvailableError, SyncLiveNodesManager
 from alternator.core.routing_scope import ClusterScope, DatacenterScope, RackScope
 from alternator.exceptions import ConfigurationError
+from tests.conftest import FakeAlternatorServer
 
 
 class TestSyncLiveNodesManager:
@@ -146,6 +149,29 @@ def mock_fetch(url: str) -> Sequence[str]:
         assert manager.refresh_nodes() is True
         assert manager.nodes.nodes == ("dc2-node1", "dc2-node2")
 
+    def test_dns_entrypoint_discovers_dns_node_records(
+        self,
+        fake_alternator_server: FakeAlternatorServer,
+    ) -> None:
+        """Discovery reaches a resolver-backed seed host and keeps DNS node records."""
+        fake_alternator_server.set_localnodes(["localhost", "node-a.internal"])
+        parsed = urlsplit(fake_alternator_server.url("/"))
+        assert parsed.port is not None
+        config = Config(
+            seed_hosts=["localhost"],
+            port=parsed.port,
+            routing_scope=ClusterScope(),
+        )
+        manager = SyncLiveNodesManager(
+            config,
+            create_sync_http_fetcher(timeout_seconds=1.0),
+        )
+
+        assert manager.refresh_nodes() is True
+
+        assert fake_alternator_server.requested_paths() == ["/localnodes"]
+        assert manager.nodes.nodes == ("localhost", "node-a.internal")
+
     def test_url_construction(self, config: Config) -> None:
         """Test URL is constructed correctly."""
         captured_url: list[str] = []