Azure Load Balancer Set traffic priority for VM1

You're correct — Azure Load Balancer (Standard or Basic) distributes traffic using a hash-based distribution algorithm and does not support affinity between ports or custom priority settings, which is why your scenario — ensuring both front-end (443) and back-end (8080) connections go to the same VM — fails. This limitation can break stateful or tightly-coupled front-end/back-end setups hosted across ports.

Option 1: Use Application Gateway with URL Path or host-based routing

Use Azure Application Gateway instead of Azure Load Balancer

• Supports Layer 7 routing logic.
• You can route based on hostname, path, or port.
• Has support for cookie-based session affinity (sticky sessions).
• Can also use custom health probes.

Implementation:

• Use App Gateway with a single listener on port 443.
• Add both VMs to the same backend pool.
• Route requests based on URL path:
  • /api/* → port 8080 on the same VM
  • Everything else → port 443

Even better if your front-end app can route to back-end via relative path (e.g., /api) instead of using different ports.

Option 2: Reverse Proxy on Each VM (e.g., Nginx/IIS/Apache)

Set up a reverse proxy like Nginx or IIS on each VM to expose only port 443, and internally route to port 8080 on localhost. This simplifies client access.

1. VM1 and VM2 accept 443 (frontend) and forwards /api to localhost:8080.
2. Load balancer now only needs to forward 443, with session affinity (source IP) enabled to ensure same VM is used for all requests.

This leaves Azure LB handling 443 only and you ensure front-end + back-end logic per VM internally.

Option 3: Use Load Balancer with Source IP Affinity

Enable "Client IP" session persistence in your load balancing rules. While it does not guarantee port affinity across multiple rules, it increases the likelihood that a client will hit the same backend for 443 and 8080 (because both rules hash from client IP). Note this is not 100% reliable — so it's not recommended if app is sensitive to split-backend behavior.

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hth

Marcin

Hi @Marcin Policht,

Could you please confirm below information.
You have an LB with A Frontend IP and a backend pool with 2 VM (running on port 8080).
Both are running same or different application?