Redirect requests to specific path to different backend port

Question

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 6,915 Microsoft External Staff Moderator

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 6,915 Reputation points Microsoft External Staff Moderator

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 2,545 Reputation points Microsoft External Staff Moderator

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.

1 answer

Your answer

Ganesh Patapati 6,915 Reputation points Microsoft External Staff Moderator

2025-03-05T12:35:27.74+00:00

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 6,915 Reputation points Microsoft External Staff Moderator

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 2,545 Reputation points Microsoft External Staff Moderator

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.

Answer 1

Hello Oscar Bergenbrink

Thanks for the reply!

We did a repro on your setup,

image (42)

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

User's image STEP 2: Backend Settings

User's image STEP 3: Custom Probe

User's image

STEP 4: Routing Rules

4.a) Default rule (80/ 443)

Listeners

User's image

Backend Targets User's image 4.b) Path Based (Web socket Traffic)

Listeners

User's image

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.

Accepted answer

KapilAnanth-MSFT 49,611 Reputation points Microsoft Employee Moderator

2025-03-10T09:56:07.1666667+00:00

@Oscar Bergenbrink ,

Welcome to the Microsoft Q&A Platform. Thank you for reaching out & I hope you are doing well.

Per your verbatim, I understand that you would like to

use Path based routing with a single listener, single backend and a different backendHttpSettings. (for a different port)

And this configured in a single Rule

Please let me know if this is incorrect. Or Are you using 2 Rules to achieve this?

See : Request Routing rules evaluation order

The priority field only impacts the order of evaluation of a request routing rule, this wont change the order of evaluation of path based rules within a PathBasedRouting request routing rule.

The priority of the routing rule should not influence the order of evaluation of path-based rules

When you say "get a invalid gateway error" - can you please share the exact error message?

Cheers,

Kapil

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