Short answer: yes, that message means the WebSocket handshake to your Prefect API timed out. In practice, persistent handshaking timeouts are almost always a network-path problem (proxy, firewall, reverse proxy not upgrading to websockets, wrong host/port, container-to-host routing), not just a “slow server”. Quick checks to pinpoint it: - Confirm the API URL your runs are using

prefect config view | grep PREFECT_API_URL

Make sure it matches how your server is exposed (http vs https). If the API is https, the WS must be wss. - From the same environment as your worker/flow, test reachability

nc -vz 10.1.37.163 4200
  curl -i <http://10.1.37.163:4200/api/health>

If you’re in Docker on a Mac, try the host alias instead:

export PREFECT_API_URL=<http://host.docker.internal:4200>

- Try a websocket handshake test client (if you have one)

websocat <ws://10.1.37.163:4200/api/events/in>

If this stalls or errors, the path is blocked. - Check for proxies/VPNs. Proxies often break WS. If you must use a proxy, add NO_PROXY for your API host:

export NO_PROXY=10.1.37.163,localhost,127.0.0.1
  export no_proxy=$NO_PROXY

Then re-run your flow/worker from that shell. - If you’re behind a reverse proxy (e.g., Nginx/Ingress), ensure WS upgrade headers and timeouts are set:

proxy_set_header Upgrade $http_upgrade;
  proxy_set_header Connection "upgrade";
  proxy_read_timeout 600s;
  proxy_send_timeout 600s;

A missing upgrade will cause timeouts during the opening handshake. - Enable debug to see the exact cause

export PREFECT_DEBUG_MODE=1

Then share the expanded error; it often reveals a proxy, TLS, or routing hint. Notes: - The endpoint Prefect uses is ws(s)://<your-api>/api/events/in. If your API is only reachable over HTTPS, you must use wss and the

PREFECT_API_URL

should be https://... - Your flows can still run, but missed WS means event data (task run details, automations) may not be recorded. If you can share a bit more: - Where is the worker/flow running (host, Docker, Kubernetes)? - Your

PREFECT_API_URL

value - Whether there’s a corporate proxy/VPN or reverse proxy in front of the API - Whether the error is intermittent or constant Related docs you can reference: - Server (Helm) and ingress notes – websocket support - Troubleshooting networking (Cloud, but proxy/NO_PROXY guidance applies)

Short answer: not exactly. It means your flow kept running, but the events websocket had an issue. What the logs are saying: - The warning/error is from the EventsWorker failing to open the websocket at

<ws://10.1.37.163:4200/api/events/in>

. That affects event streaming (e.g., real‑time logs/observability), not the execution of the flow itself. - “Service 'EventsWorker' failed with 1 pending items” means at least one event could not be sent and was dropped. - “Beginning flow run …” shows the flow execution proceeded anyway. So the run didn’t crash, but the events channel wasn’t connected at that moment. How to tell if it recovered: - If it recovers, you’ll typically stop seeing the websocket warnings and you’ll see logs/events in the UI again. With debug on, you may see a message indicating a successful connection. - Turn on extra detail to confirm: set

PREFECT_DEBUG_MODE=1

(as the log suggests) and/or

PREFECT_LOGGING_LEVEL=DEBUG

to get fuller messages about retries/reconnections. What to check to fix the websocket: - Network path from where the flow runs to `http://10.1.37.163:4200`: - Firewalls/security groups allowing port 4200 - Proxies/load balancers/ingress configured to allow WebSocket upgrades (e.g., NGINX must pass `Upgrade`/`Connection: upgrade`) - Make sure

PREFECT_API_URL

is correct and reachable from the runtime. If your API is HTTPS, the events URL should be

wss://...

(Prefect derives this automatically from

PREFECT_API_URL

). - If you’re self‑hosting behind an ingress/Helm, validate the service/ingress supports websockets and the events endpoint. - For worker/process resiliency, healthchecks can help keep processes alive if there are transient issues. Helpful references: - Worker healthchecks - Prefect Server Helm If you can share a few more lines after those logs, I can confirm whether the EventsWorker reconnected or if it’s still failing. Are you running a self‑hosted API at 10.1.37.163 behind a proxy or firewall?