Azure Traffic Manager

After gaining a good understanding of both the Azure load balancer and the application gateway, it's time to get into the details of Traffic Manager. Azure load balancers and application gateways are much-needed resources for high availability within a data center and region; however, to achieve high availability across regions and data centers, there is a need for another resource, and that is Traffic Manager.

Traffic Manager helps us to create highly available solutions that span multiple geographies, regions, and data centers. Traffic Manager is not similar to load balancers. It uses DNS to redirect requests to an appropriate endpoint determined by their health and configuration. Traffic Manager is not a proxy or a gateway. Traffic Manager does not see the traffic passing between the client and the service. It simply redirects the request based on the most appropriate endpoints.

Azure Traffic Manager enables you to control the distribution of traffic across your application endpoints. An endpoint is any internet-facing service hosted inside or outside of Azure.

Endpoints are internet-facing, reachable public URLs. Applications are provisioned within multiple geographies and Azure regions. Applications deployed to each region have a unique endpoint referred by DNS CNAME. These endpoints are mapped to the Traffic Manager endpoint. When a Traffic Manager is provisioned, it gets an endpoint by default with a .trafficmanager.net URL extension.

When a request arrives at the Traffic Manager URL, it finds the most appropriate endpoint out of its list and redirects the request to it. In short, Traffic Manager acts as a global DNS to identify the region that will serve the request.

However, how does Traffic Manager know which endpoints to use and redirect the client request to? There are two aspects that the Traffic Manager implements to determine the most appropriate endpoint and region.

First, Traffic Manager actively monitors the health of all endpoints. It can monitor the health of VMs, cloud services, and app services. If it determines that the health of an application deployed to a region is not suitable for redirecting traffic, it redirects the requests to a healthy endpoint.

Second, the Traffic Manager can be configured with routing information. There are four traffic routing methods available in Traffic Manager, which are as follows:

• Priority: Should be used when all traffic should go to a default endpoint, and backups are available in case the primary endpoints are unavailable.
• Weighted: Should be used to distribute traffic across endpoints evenly, or according to defined weights.
• Performance: Should be used for endpoints in different regions, and users should be redirected to the closest endpoint based on their location. This has a direct impact on network latency.
• Geographic: This should be used to redirect users from a specific geography to an endpoint (Azure, external, or nested) available in that geography or nearest to that geography. Examples include complying with data sovereignty mandates, localization of content and user experience, and measuring traffic from different regions.
• Subnet: This is a new routing method added and it helps in providing clients different endpoints based on their IP addresses. In this method, a range of IP addresses are assigned to each endpoint. These IP address ranges are mapped to the client IP address to determine an appropriate returning endpoint. Using this routing method, it is possible to provide different content to different people based on their originating IP address. 
• Multivalue: This is also a new method added in Azure. In this method, multiple endpoints are returned back to the client and any of them can be used. This ensures that if one endpoint is unhealthy, other endpoints can be used. This helps in increasing the overall availability of the solution.

It should be noted that after the Traffic Manager determines a valid healthy endpoint, clients connect directly to the application.