Cap the default backend worker count (#7542)

* Cap automatically selected backend workers

* Test capped backend worker defaults

* Document capped backend worker default

* Document capped backend worker default

* Document capped backend worker default

* Document capped backend worker default

* Add release note for worker cap

* Clarify Granian worker override scope

* Clarify Granian worker override scope

* Clarify Granian worker override scope

* Clarify Granian worker override scope

* Update docs/hosting/self-hosting.md

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

---------

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

Author: harsh21234i

docker-example/app-platform-backend/README.md

@@ -38,8 +38,9 @@ The backend is built by the `Dockerfile` in this directory. When deploying the
 backend, be sure to set REFLEX_REDIS_URL=redis://internal-redis-hostname to connect to
 the redis service.
 
-With redis available, each replica runs `2 * cpu_count + 1` worker processes.
-Set `GRANIAN_WORKERS` to cap this on small instance sizes.
+With redis available, each replica runs up to 8 workers by default
+(`2 * cpu_count + 1`, capped at 8). When using Granian, set `GRANIAN_WORKERS`
+to override the default, including to use more workers.
 
 If the app uses postgres, add `psycopg[binary]` to `requirements.txt`; the
 binary wheel bundles libpq, so no extra system packages are needed in the image.

docker-example/production-compose/README.md

@@ -68,9 +68,9 @@ Add `psycopg[binary]` to `requirements.txt` so the backend can connect to
 postgres; the binary wheel bundles libpq, so no extra system packages are
 needed in the image.
 
-With redis available, the backend runs `2 * cpu_count + 1` worker processes.
-Set `GRANIAN_WORKERS` in the `app` environment to cap this on memory
-constrained hosts.
+With redis available, the backend runs up to 8 workers by default (`2 * cpu_count + 1`,
+capped at 8). When using Granian, set `GRANIAN_WORKERS` in the `app` environment
+to override the default, including to use more workers.
 
 Postgres uses its own named docker volume for data persistence.
 

docker-example/production/README.md

@@ -31,8 +31,8 @@ To listen on a different port, pass `--build-arg PORT=10000`.
 docker run -p 8080:8080 reflex-production
 ```
 
-By default the backend runs `2 * cpu_count + 1` workers. Set `GRANIAN_WORKERS`
-to a smaller number in memory constrained environments:
+By default the backend runs up to 8 workers (`2 * cpu_count + 1`, capped at 8).
+When using Granian, set `GRANIAN_WORKERS` to override the default, including to use more workers:
 
 ```console
 docker run -e GRANIAN_WORKERS=2 -p 8080:8080 reflex-production

docs/hosting/self-hosting.md

@@ -44,8 +44,8 @@ Production mode compiles the app, builds an optimized static frontend, and
 serves it together with the backend (event websocket, `/ping`, `/_upload`)
 from a single server on port `3000`. Pass `--frontend-port` or
 `--backend-port` to listen on a different port. When redis is configured,
-the server runs `2 * cpu_count + 1` worker processes; set `GRANIAN_WORKERS`
-to override this.
+the server runs up to 8 backend workers by default (`2 * cpu_count + 1`, capped at 8).
+When using Granian, set `GRANIAN_WORKERS` to override the default, including to use more workers.
 
 The frontend and backend can also run as separate processes, for example to
 serve the frontend from a CDN and scale the backend independently. The

news/+cap-default-backend-workers.bugfix.md

@@ -0,0 +1 @@
+Cap the automatically selected number of Redis-backed backend workers at eight. Set `GRANIAN_WORKERS` to override the default.

reflex/utils/processes.py

@@ -29,6 +29,8 @@
 
 logger = logging.getLogger(__name__)
 
+MAX_BACKEND_WORKERS = 8
+
 
 def kill(pid: int):
     """Kill a process.
@@ -61,7 +63,7 @@ def get_num_workers() -> int:
     except RedisError as re:
         logger.error(f"Unable to connect to Redis: {re}")
         raise SystemExit(1) from None
-    return (os.cpu_count() or 1) * 2 + 1
+    return min((os.cpu_count() or 1) * 2 + 1, MAX_BACKEND_WORKERS)
 
 
 def _can_bind_at_port(

tests/units/utils/test_processes.py

@@ -29,6 +29,27 @@
 )
 
 
+@pytest.mark.parametrize(
+    ("cpu_count", "expected"),
+    [(None, 3), (0, 3), (1, 3), (2, 5), (3, 7), (4, 8), (64, 8)],
+)
+def test_get_num_workers_caps_automatic_worker_count(cpu_count, expected):
+    """Cap automatic worker counts while preserving the CPU-based default below the cap."""
+    redis_client = mock.Mock()
+    with (
+        mock.patch.object(
+            processes, "get_config", return_value=mock.Mock(transport="websocket")
+        ),
+        mock.patch.object(
+            processes.prerequisites, "get_redis_sync", return_value=redis_client
+        ),
+        mock.patch.object(processes.os, "cpu_count", return_value=cpu_count),
+    ):
+        assert processes.get_num_workers() == expected
+
+    redis_client.ping.assert_called_once_with()
+
+
 def test_is_process_on_port_free_port():
     """Test is_process_on_port returns False when port is free."""
     # Find a free port