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Based on your questions above
I want to find out from the last 3 days, all public IPs who was connected to my azure load balancer and also all public IPs connections initiated from my Loadbalancer.
As original source IP address is preserved when the traffic passes through Azure Load Balancer, I think in order to get details on public IPs connecting via the Load balancer you can enable NSG Flow logs for the NSG of the subnet containing all the backend VMs. Network security groups flow logging is a feature of Azure Network Watcher that allows you to log information about IP traffic flowing through a network security group. You need to know the current state of the network, who's connecting, and where users are connecting from. You also need to know which ports are open to the internet, what network behavior is expected, what network behavior is irregular, and when sudden rises in traffic happen.
Although if you are enabling the flow logs for the NSG now, the data from last 3 days will not be available. As the data is captured and stored in the storage account as soon as the feature is enabled. Please let me know if you wish to perform analyses on any last 3 days data only.
Also I want to find the load for each node/VMs behind this LB( last 3 days)
Not exactly sure about what exactly you are trying to find here but you can take a look at Load Balancer metrics and see if you are able to view the required details.
Hope this helps! Please let me know if you have any additional questions. Thank you!
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