Azure PubSub Connection Timeout (ETIMEDOUT)

Question

Azure PubSub Connection Timeout (ETIMEDOUT)

Ashir Baig 0

I have provisioned an Azure Web PubSub service by following the official Azure documentation. The service has been configured using the JSON settings provided below. In addition, a secondary replica has been set up successfully, and its configuration details are also included.

Despite this setup, we are consistently encountering a connection timeout error (ETIMEDOUT) when attempting to connect to the Azure Web PubSub service. The issue occurs during client connection attempts and impacts message delivery.

This service is actively used in our production environment, and the timeout is causing service disruption.
Additional Technical Context:

Azure Web PubSub Service is deployed and running
Primary and secondary replicas are enabled
Error occurs during client connection attempts to the service endpoint
Error message observed: ETIMEDOUT
Configuration has been validated against Azure documentation
Application server load is within normal operating limits (CPU, memory, and network utilization are stable and not saturated at the time the issue occurs)

Please let us know if additional details required

Edited PII information

Golla Venkata Pavani 7,535 Reputation points Microsoft External Staff Moderator

2026-01-22T09:28:28.1066667+00:00

Hi @Ashir Baig ,

Thank you for reaching us about the issue of ETIMEDOUT connection error with your Azure Web PubSub service.

We have begun looking into it and will share our suggestions with you as soon as possible. If you have any additional details or concerns in the meantime, please let us know. We appreciate your patience while we work on this.
Ashir Baig 0 Reputation points

2026-01-23T12:31:11.75+00:00

Hi @Praneeth Maddali ,

Thank you for your detailed response and suggestions.

I would like to clarify that in our setup, we are using the primary PubSub endpoint and not the client/secondary replica. During sessions, we are able to successfully connect in some cases, while in others, the connection times out with ETIMEDOUT.

This inconsistency does not appear to be related to the secondary endpoint, as all connection attempts are directed to the primary FQDN. Any additional insights you may have on why connections succeed intermittently would be greatly appreciated.
Praneeth Maddali 12,670 Reputation points Microsoft External Staff Moderator

2026-01-23T13:10:24.4966667+00:00

Hi @Ashir Baig

Thank you for the clarification — that helps narrow things down. Since all of your connections are targeting the primary Web PubSub endpoint, the intermittent ETIMEDOUT behavior is typically caused by factors outside the Web PubSub service itself. When some connections succeed and others time out, the root cause is usually related to network path reliability, token validity, or client-side connection behavior, rather than the replica configuration.

We have clarified this in our comment

Kindly let us know if the above helps or you need further assistance on this issue.

Please "upvote" if the information helped you. This will help us and others in the community as well.
Golla Venkata Pavani 7,535 Reputation points Microsoft External Staff Moderator

2026-01-27T09:55:31.3166667+00:00

Hi @Ashir Baig

I'm just reaching out to see if your issue has been resolved or if you've had a chance to review our previous comment?

2 answers

Your answer

Golla Venkata Pavani 7,535 Reputation points Microsoft External Staff Moderator

2026-01-22T09:28:28.1066667+00:00

Hi @Ashir Baig ,

Thank you for reaching us about the issue of ETIMEDOUT connection error with your Azure Web PubSub service.

We have begun looking into it and will share our suggestions with you as soon as possible. If you have any additional details or concerns in the meantime, please let us know. We appreciate your patience while we work on this.
Ashir Baig 0 Reputation points

2026-01-23T12:31:11.75+00:00

Hi @Praneeth Maddali ,

Thank you for your detailed response and suggestions.

I would like to clarify that in our setup, we are using the primary PubSub endpoint and not the client/secondary replica. During sessions, we are able to successfully connect in some cases, while in others, the connection times out with ETIMEDOUT.

This inconsistency does not appear to be related to the secondary endpoint, as all connection attempts are directed to the primary FQDN. Any additional insights you may have on why connections succeed intermittently would be greatly appreciated.
Praneeth Maddali 12,670 Reputation points Microsoft External Staff Moderator

2026-01-23T13:10:24.4966667+00:00

Hi @Ashir Baig

Thank you for the clarification — that helps narrow things down. Since all of your connections are targeting the primary Web PubSub endpoint, the intermittent ETIMEDOUT behavior is typically caused by factors outside the Web PubSub service itself. When some connections succeed and others time out, the root cause is usually related to network path reliability, token validity, or client-side connection behavior, rather than the replica configuration.

We have clarified this in our comment

Kindly let us know if the above helps or you need further assistance on this issue.

Please "upvote" if the information helped you. This will help us and others in the community as well.
Golla Venkata Pavani 7,535 Reputation points Microsoft External Staff Moderator

2026-01-27T09:55:31.3166667+00:00

Hi @Ashir Baig

I'm just reaching out to see if your issue has been resolved or if you've had a chance to review our previous comment?

Answer 1

Hi @Ashir Baig

Thanks for clearly describing the issue. I understand that this timeout is impacting your production service, and it can be very frustrating, especially when everything else appears to be working well.

Most Likely Cause:

With replicas enabled, such as your secondary setup, clients should connect only to the primary endpoint: wss://connectlingua-jp-pubsub-prod.webpubsub.azure.com/client/hubs/myhub?access_token=...

Connecting to the secondary replica endpoint (connectlingua-jp-pubsub-sec-prod) will always result in an ETIMEDOUT error.

Quick Diagnostic Steps :

Check the endpoint: Make sure your app code is using the primary FQDN above and not "sec-prod."

Test connectivity: Try connecting from your client machine or server.

   npm install -g wscat
   wscat -c "wss://connectlingua-jp-pubsub-prod.webpubsub.azure.com/client/hubs/myhub?access_token=YOUR_TOKEN"

Check networking: Portal >Web PubSub > Networking > Access Restrictions > Allow "All networks" temporarily
Enable Live Trace: Portal >Monitoring > Live Trace >Enable > Try connecting >Check for events

Expected Results:

If wscat connects successfully, the endpoint is healthy — this means the issue is in your client application code. You should fix your app’s connection string.
If wscat times out, there is a network blockage preventing the connection. You should check your firewall or proxy settings, especially ensuring port 443 is open.
If Live Trace is empty, the request is not reaching Azure at all. This indicates a client-side network or proxy block, so review your network rules or proxy configuration.
If Live Trace shows events, Azure is receiving the connection attempts. At this point, you should check your authentication token and application logs, because the issue is likely related to auth or app logic.

Below are the most common reasons this occurs and how to isolate them.

Reasons for Intermittent Connection Success and Timeouts Network Instability (firewall, proxy, VPN, ZTNA, TLS inspection): WebSockets need a steady outbound route over port 443. If a firewall or proxy sometimes delays or blocks the TLS/WebSocket handshake, those attempts may fail with ETIMEDOUT.

Network access control & outbound requirements: https://learn.microsoft.com/azure/azure-web-pubsub/howto-secure-network-access-control Token Expiry or Reuse Under Load:

If several clients use a short-lived or soon-to-expire access token, some connections may succeed while others fail at handshake. Authentication and token behavior: https://learn.microsoft.com/azure/azure-web-pubsub/howto-troubleshoot-common-issues#authentication-…

Client-Side Connection Surges and Throttling:

If many connections are started at once, handshake processes may slow down and hit timeout limits.

Connection count / throttling rules https://learn.microsoft.com/azure/azure-web-pubsub/concepts-service-constraints

Recommended Steps for Determining the Root Cause

Conduct multiple connectivity tests using wscat from the same client environment

This approach helps determine if the issue is related to the client network:

Knowledge base

npm install -g wscat
wscat -c "wss://connectlingua-jp-pubsub-prod.webpubsub.azure.com/client/hubs/myhub?access_token=YOUR_FRESH_TOKEN"

If the results are inconsistent, such as 5 out of 10 being successful, this indicates that the network path is unstable.

Enable Live Trace and compare successful and failed attempts from Portal > Web PubSub > Monitoring > Live Trace

Check for:

No events at all – the client did not reach Azure, possibly due to a network or proxy block
PingTimeout / SlowClient – handshake is taking too long on the client side
Authentication errors – token may be close to expiration

Reference:

https://learn.microsoft.com/en-us/azure/azure-web-pubsub/howto-troubleshoot-resource-logs

https://learn.microsoft.com/en-us/azure/azure-web-pubsub/howto-enable-geo-replication?tabs=Portal

https://learn.microsoft.com/en-us/azure/azure-web-pubsub/howto-troubleshoot-common-issues

https://learn.microsoft.com/en-us/azure/azure-web-pubsub/howto-troubleshoot-resource-logs

https://learn.microsoft.com/en-us/azure/azure-web-pubsub/howto-secure-network-access-control?tabs=azure-portal

Kindly let us know if the above helps or you need further assistance on this issue.

Please "upvote" if the information helped you. This will help us and others in the community as well.

Answer 2

The connection timeout error (ETIMEDOUT) you are experiencing when trying to connect to the Azure Web PubSub service can be caused by several factors. Here are some troubleshooting steps you can take to address this issue:

Verify Connection String: Ensure that the connection string or fully qualified domain name specified when creating the client is correct. Any errors in the connection string can lead to timeouts.
Firewall and Port Permissions: Check the firewall settings in your hosting environment to ensure that the necessary ports for Azure Web PubSub are open. The service typically uses ports 443 for WebSockets and 80 for HTTP.
Network Configuration: Ensure that your network is not blocking specific IP addresses that are required for Azure Web PubSub. You may need to allowlist certain IPs to ensure connectivity.
Proxy Configuration: If your application is behind a proxy, verify that the proxy settings are correctly configured. An intercepting proxy can cause SSL handshake failures, leading to connection timeouts.
Service Status: Check the Azure service status to see if there are any ongoing issues or maintenance that could affect connectivity.
Resource Logs: Utilize resource logs to identify any unexpected disconnection events or connection limits being reached. Look for entries like Connection count reaches limit or other relevant messages that could indicate issues.
Client Performance: Ensure that the client is capable of handling the current traffic load. If clients are not able to process messages quickly enough, it may lead to timeouts.

By following these steps, you should be able to identify the root cause of the ETIMEDOUT error and take appropriate action to resolve it.

References: