Load balancer

• Load balancer can be attached to a Virtual Machine Scale Set (VMSS)
• When a new instance of VMSS is added, it's automatically added to the backend pool
• A LB must be assigned a Public IP (Frontend IP)

Configuration

• A backend pool must be added. They are the VMs
• A frontend IP is the IP of the LB
• A health probe can be added for health check of VMs (Like a ping request, hearthbeat). The health probe is applied to test all the VMs
• A load balancing rule must be added with routing rules
• front ip address, port, protocol, etc

SKUs

• Basic: Single VM, Availability Set, Scale Set
• Standard: Multiple VMs, Availability Set, Scale Set. Provides 99.99% SLA
• Requires standard Public IP
• Requires NICs to have static IP address and a NSG

Internal vs External LBs

• External (Public): Connection from outside internet
• Internal: Connection from within the VNet

Inbound NAT (Network Address Translation) rules

• NAT types
• Static: one private IP is mapped to one public IP
• Dynamic: one private IP is mapped to a pool of public IPs
• PAT (Port Address Translation): single public IP mapped to multiple private IPs using port numbers
• When you want to specific exactly which machine you want the LB to redirect you to. For example if you want to SSH this machine
• The NAT rules is performed by specifying a port to the LB frontendIP (PAT)
• E.g., Port 4000 (public ip) redirects to port 22 in VM1 (private ip), Port 4001 (public ip) redirects to port 22 in VM2 (private ip)

Load Balancer Diagnostic logs (Basic LB)

• Diagnostic logs can be activated under Diagnostic settings tab
• 2 log entries that can be generated
• LB Alert Event (continuously)
• LB Probe Health Status Health probe log (Only if there is an issue)
• The logs can be sent to
• Log Analytics Workspace
• Storage Account
• Azure Event Hub

Load Balancer Metrics (Standard LB)

• Access under Metrics tab
• Metrics
• Health Probe Status
• Data Path Availability
• Charts can be displayed to visualize the logs

Load Balancer Insights

• This feature is provided as part of Azure Monitor
• Accessible under Insights tab
• Features
• Visualize the design of the LB
• Detail metrics of the LB: Availability, Throughput, Flow Distribution, Latency