Redirect requests to specific path to different backend port

Oscar Bergenbrink 0

Hi.

We have an application gateway and then one host in the backend pool. We have a listner on 443 and then a rule which sends that traffic over to the backendpool on a specific port. However, there's a chat in the backend application which wants to do some connections on another port when you send a request to /websocket. We have tried to make this work with: another backend setting which has the other port. And then a path-based rule with "path = /websocket*, Target name = websocket, Backend setting name = name of the other backend setting, Backend pool = our 1 and only pool".

When I have the "normal" rule as highest prio, all normal operations work but the /websocket requests are not treated differently, and when I change the path-based rule to have a higher priority I get a invalid gateway error.

To sum it up the goal is:
Rule 1 = send 443 requests to backend
Rule 2 = send /websocket to same backend but with a specified port

Ganesh Patapati 4,150 Microsoft External Staff

Hi Oscar Bergenbrink

Greetings!

To configure your Azure Application Gateway to handle both normal HTTPS traffic and WebSocket traffic on different ports, please follow the below configuration setup.

Component	Default Rule	WebSocket Rule
Listener	443 (HTTPS)	Same listener (443)
Listener	443 (HTTPS)	Same listener (443)
Backend Pool	BackendHost:80	BackendHost:8080
HTTP Setting	Port 80	Port 8080 + Valid Probe
Path	/* (catch-all)	/websocket
Priority	Lower (e.g., 100)	Higher (e.g. 50)

Also please verify the Unhealthy instances in BackendAddressPool

Can you please update us if the action plan provided by was helpful?

Should there be any follow-up questions or concerns, please let us know and we shall try to address them.

Oscar Bergenbrink 0 Reputation points

2025-03-05T12:51:35.29+00:00

Hi,

So pretty much as I tried but I made a mistake by not having a second backend pool for the custom port?
Oscar Bergenbrink 0 Reputation points

2025-03-05T13:00:34.9466667+00:00

But.. I dont understand this answer - you don't control backend ports in the pool, you do that in the backend settings. Right? So then I don't see the difference in this suggestion from what I've already tried.
Ganesh Patapati 4,150 Reputation points Microsoft External Staff

2025-03-05T15:23:22.7+00:00
Hello Oscar Bergenbrink

Thanks for the reply!

We did a repro on your setup,

And, would like to inform you that separate listeners need to be created to handle port 80/443 traffic and another port (e.g., 8080 for websocket traffic).

Additionally, separate routing rules must be created to map the HTTP/HTTPS traffic and another routing rule with path-based routing for websocket traffic.

Please ensure that separate backend HTTP settings are configured: one for HTTP/HTTPS and another for port 8080. You can configure a single backend pool to accept both HTTP/HTTPS and websocket traffic (e.g., port 8080).

NOTE: you cannot use two listeners with same frontend port on same application gateway Public IP

MY LAB SETUP:

STEP 1: Listener configuration

STEP 2: Backend Settings

STEP 3: Custom Probe

STEP 4: Routing Rules

4.a) Default rule (80/ 443)

Listeners

Backend Targets 4.b) Path Based (Web socket Traffic)

Listeners

If you want to see the test results I am posting via private messages, were you able to validate them.

Can you please update us if the action plan provided by was helpful?

Please accept an answer if correct. Original posters help the community find answers faster by identifying the correct answer. Here is how.
Ganesh Patapati 4,150 Reputation points Microsoft External Staff

2025-03-06T13:39:52.0333333+00:00

Hi Oscar Bergenbrink

Can you please update us if the action plan provided by was helpful?

Should there be any follow-up questions or concerns, please let us know and we shall try to address them.
Venkat V 775 Reputation points Microsoft External Staff

2025-03-07T07:56:57.3233333+00:00

Hi @Oscar Bergenbrink

Can you please share a screenshot of your rules, backend settings, and listener configuration for more clarification?

Also, confirm which port you are using for WebSocket.

Note: If the backend application is not configured to use ports 80 or 443, WebSockets will not work as they only support these ports. Additionally, the backend health probe also supports only HTTP (80) and HTTPS (443).

Reference: WebSocket enabled backend

I hope this helps to resolve your issue.

If the above is unclear and/or you are unsure about something, add a comment below.

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