Use a Docker healthcheck for the Flask servers

pyproject.toml

@@ -337,6 +337,9 @@ cumulative_timing = false
 [tool.coverage.run]
 
 branch = true
+omit = [
+    "src/mock_vws/_flask_server/healthcheck.py",
+]
 
 [tool.coverage.report]
 

src/mock_vws/_flask_server/Dockerfile

@@ -20,6 +20,7 @@ RUN pip install --no-cache-dir uv==0.1.44 && \
     uv pip install --no-cache-dir --upgrade --editable .
 EXPOSE 5000
 ENTRYPOINT ["python"]
+HEALTHCHECK --interval=1s --timeout=10s --start-period=5s --retries=3 CMD ["python", "/app/src/mock_vws/_flask_server/healthcheck.py"]
 
 FROM base as vws
 ENV VWS_HOST=0.0.0.0

src/mock_vws/_flask_server/healthcheck.py

@@ -0,0 +1,32 @@
+"""
+Health check for the Flask server.
+"""
+
+import http.client
+import socket
+import sys
+from http import HTTPStatus
+
+
+def flask_app_healthy(port: int) -> bool:
+    """
+    Check if the Flask app is healthy.
+    """
+    conn = http.client.HTTPConnection("localhost", port)
+    try:
+        conn.request("GET", "/some-random-endpoint")
+        response = conn.getresponse()
+    except (TimeoutError, http.client.HTTPException, socket.gaierror):
+        return False
+    finally:
+        conn.close()
+
+    return response.status in {
+        HTTPStatus.NOT_FOUND,
+        HTTPStatus.UNAUTHORIZED,
+        HTTPStatus.FORBIDDEN,
+    }
+
+
+if __name__ == "__main__":
+    sys.exit(int(not flask_app_healthy(port=5000)))

tests/mock_vws/test_docker.py

@@ -23,12 +23,11 @@
     import io
     from collections.abc import Iterator
 
+    from docker.models.containers import Container
     from docker.models.images import Image
     from docker.models.networks import Network
 
 
-# We do not cover this function because hitting particular branches depends on
-# timing.
 @retry(
     wait=wait_fixed(wait=0.5),
     stop=stop_after_delay(max_delay=20),
@@ -37,21 +36,18 @@
     ),
     reraise=True,
 )
-def wait_for_flask_app_to_start(base_url: str) -> None:  # pragma: no cover
+def wait_for_health_check(container: Container) -> None:
     """
-    Wait for a server to start.
-
-    Args:
-        base_url: The base URL of the Flask app to wait for.
+    Wait for a container to pass its health check.
     """
-    url = f"{base_url}/{uuid.uuid4().hex}"
-    response = requests.get(url=url, timeout=30)
-    if response.status_code not in {
-        HTTPStatus.NOT_FOUND,
-        HTTPStatus.UNAUTHORIZED,
-        HTTPStatus.FORBIDDEN,
-    }:
-        error_message = f"Could not connect to {url}"
+    container.reload()
+    health_status = container.attrs["State"]["Health"]["Status"]
+    # In theory this might not be hit by coverage.
+    # Let's keep it required by coverage for now.
+    if health_status != "healthy":
+        error_message = (
+            f"Container {container.name} is not healthy: {health_status}"
+        )
         raise ValueError(error_message)
 
 
@@ -186,6 +182,7 @@
     )
 
     for container in (target_manager_container, vws_container, vwq_container):
+        wait_for_health_check(container=container)
         container.reload()
 
     target_manager_port_attrs = target_manager_container.attrs[
@@ -213,9 +210,6 @@
         f"http://{target_manager_host_ip}:{target_manager_host_port}"
     )
 
-    for base_url in (base_vws_url, base_vwq_url, base_target_manager_url):
-        wait_for_flask_app_to_start(base_url=base_url)
-
     response = requests.post(
         url=f"{base_target_manager_url}/databases",
         json=database.to_dict(),