tests: make test_change_pageserver more robust (#8442)

## Problem

This test predates the storage controller. It stops pageservers and
reconfigures computes, but that races with the storage controller's node
failure detection, which can result in restarting nodes not getting the
attachments they expect, and the test failing

## Summary of changes

- Configure the storage controller to use a compute notify hook that
does nothing, so that it cannot interfere with the test's configuration
of computes.
- Instead of using the attach hook, just notify the storage controller
that nodes are offline, and reconcile tenants so that they will
automatically be attached to the other node.

test_runner/regress/test_change_pageserver.py

@@ -3,9 +3,16 @@ import asyncio
 from fixtures.log_helper import log
 from fixtures.neon_fixtures import NeonEnvBuilder
 from fixtures.remote_storage import RemoteStorageKind
+from werkzeug.wrappers.request import Request
+from werkzeug.wrappers.response import Response
 
 
-def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
+def test_change_pageserver(neon_env_builder: NeonEnvBuilder, make_httpserver):
+    """
+    A relatively low level test of reconfiguring a compute's pageserver at runtime.  Usually this
+    is all done via the storage controller, but this test will disable the storage controller's compute
+    notifications, and instead update endpoints directly.
+    """
     num_connections = 3
 
     neon_env_builder.num_pageservers = 2
@@ -14,9 +21,24 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
     )
     env = neon_env_builder.init_start()
 
+    neon_env_builder.control_plane_compute_hook_api = (
+        f"http://{make_httpserver.host}:{make_httpserver.port}/notify-attach"
+    )
+
+    def ignore_notify(request: Request):
+        # This test does direct updates to compute configuration: disable the storage controller's notification
+        log.info(f"Ignoring storage controller compute notification: {request.json}")
+        return Response(status=200)
+
+    make_httpserver.expect_request("/notify-attach", method="PUT").respond_with_handler(
+        ignore_notify
+    )
+
     env.neon_cli.create_branch("test_change_pageserver")
     endpoint = env.endpoints.create_start("test_change_pageserver")
 
+    # Put this tenant into a dual-attached state
+    assert env.get_tenant_pageserver(env.initial_tenant) == env.pageservers[0]
     alt_pageserver_id = env.pageservers[1].id
     env.pageservers[1].tenant_attach(env.initial_tenant)
 
@@ -72,6 +94,7 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
     env.pageservers[
         0
     ].stop()  # Stop the old pageserver just to make sure we're reading from the new one
+    env.storage_controller.node_configure(env.pageservers[0].id, {"availability": "Offline"})
 
     execute("SELECT count(*) FROM foo")
     assert fetchone() == (100000,)
@@ -82,9 +105,10 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
     #
     # Since we're dual-attached, need to tip-off storage controller to treat the one we're
     # about to start as the attached pageserver
-    env.storage_controller.attach_hook_issue(env.initial_tenant, env.pageservers[0].id)
     env.pageservers[0].start()
     env.pageservers[1].stop()
+    env.storage_controller.node_configure(env.pageservers[1].id, {"availability": "Offline"})
+    env.storage_controller.reconcile_until_idle()
 
     endpoint.reconfigure(pageserver_id=env.pageservers[0].id)
 
@@ -92,10 +116,9 @@ def test_change_pageserver(neon_env_builder: NeonEnvBuilder):
     assert fetchone() == (100000,)
 
     env.pageservers[0].stop()
-    # Since we're dual-attached, need to tip-off storage controller to treat the one we're
-    # about to start as the attached pageserver
-    env.storage_controller.attach_hook_issue(env.initial_tenant, env.pageservers[1].id)
     env.pageservers[1].start()
+    env.storage_controller.node_configure(env.pageservers[0].id, {"availability": "Offline"})
+    env.storage_controller.reconcile_until_idle()
 
     # Test a (former) bug where a child process spins without updating its connection string
     # by executing a query separately. This query will hang until we issue the reconfigure.