An architectural pattern that can be used to build loosely-coupled systems is N-tier
This divides an architecture into two or more logical tiers. Architecturally, a higher tier can access services from a lower tier, but a lower tier should never access a higher tier.
Tiers help separate concerns and ideally are designed to be reusable. Using a tiered architecture also simplifies maintenance. Tiers can be updated or replaced independently, and new tiers can be inserted if needed.
A virtual network allows Azure resources to securely communicate with each other, the internet and on premises networks.
A virtual network is scoped to a single region; however, multiple virtual networks from different regions can be connected together using virtual network peering.
Virtual networks can be segmented into one or more subnets to allow you to organize and secure your resources into discrete sections.
For VMs that the users interact with directly, such as the web tier, the VM will have both a public and private IP, whereas other tiers will just have private IPs.
This allows or denies inbound network traffic to your Azure resources in a similar way to a firewall.
The user connects to the load balancer, which then decides which Virtual Machine will process the request. This also allows you to run maintenance tasks without interrupting service as the load balancer detects that the VM is unresponsive and directs traffic to other VMs in the pool.
You can use it with:
Incoming internet traffic
Internal traffic across Azure services
Port forwarding for specific traffic
Outbound connectivity for VMs in your virtual network
With Azure load balancer, there’s no infrastructure or software to maintain, just a set of rules.
Azure Application gateway is a load balancer for web applications. It uses Azure Load balancer at the transport level but uses routing rules for more advanced scenarios.
Benefits over a load balancer:
Web application firewall
URL rule based routes
Rewrite HTTP headers
One way to improve network latency is to scale out exact copies of your service to more than one region
Azure Traffic Manager uses the DNS server that’s closest to the user to direct user traffic to a globally distributed endpoint.