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Design Microsoft Azure Infrastructure and Networking

Objective 1.5: Describe Azure Services

Because your solution spans across multiple regions and facilities, you need to take additional care to ensure that the system performs at a global level. This objective introduces a couple of Azure services that can help you to optimize performance of a globally distributed system. Chapter 4 introduces more Azure services in the contexts of different scenarios.

Using Azure Traffic Manager

Traffic Manager routes incoming traffic to your application deployments at different geographic locations based on performance and availability.

To use Traffic Manager, you define a Traffic Manager profile that consists of a domain name, a list of endpoints, and a load-balancing policy. When a user tries to access a service, the following activities happen:

  1. The user accesses the service by the domain name provided by Traffic Manager (*.trafficmanager.net). If a custom domain is used, another DNS resolution is performed to first resolve the custom domain name to the Traffic Manager domain name.
  2. When Traffic Manager receives the DNS resolution request, it evaluates its policy and picks an endpoint address based on availability, performance, or a round-robin policy.
  3. Traffic Manager returns a CNAME record that maps the Traffic Manager domain name to the selected endpoint.
  4. The user’s DNS server resolves the endpoint address to its IP address and sends it to the user.
  5. The user calls the endpoint directly by the IP address.

A couple of points are worth discussing here. First, Traffic Manager functions during the DNS resolution phase. The actual traffic doesn’t go through Traffic Manager. Second, because DNS records are often cached, Traffic Manager isn’t involved in every service request. Third, the endpoints don’t need to be on Azure. They can be on other cloud platforms, or even in on-premises datacenters.

Traffic Manager picks endpoints based on one of the following three methods:

  • Round-robin Traffic is distributed to all endpoints evenly or based on weights.
  • Performance Traffic Manager periodically updates a table that records the response time between various IP ranges to Azure datacenters. When a new request comes in, it picks the datacenter with the best response time in corresponding IP range.
  • Failover Traffic Manager returns the primary endpoint by default. However, if the primary endpoint becomes unavailable, it will return backup endpoints according to their assigned priorities.

These three methods are suitable for different scenarios. The round-robin method can be used for load-balancing in a same region or across multiple regions. The performance method can be used to optimize user traffic distribution. And the failover method can be used in failover scenarios.

You can also nest Traffic Manager profiles, which means a profile at a higher level uses other Traffic Manager endpoints as candidate endpoints. Using nested profiles, you can implement more complex policies. For example, you can have a top-level profile that uses the failover method to establish a primary site and a secondary site, and a second-level profile that distributes user traffics based on performance. You can have up to 10 levels of nested profiles.

Using CDN

Azure operates out of facilities located in 17 regions around the world, and that number is increasing every year. In addition, Azure also strategically places CDN point of presence (POP) locations to deliver content to end users. You can cache content from Azure Storage, Web Apps, and Azure Cloud Services.

When a user requests content by the CDN URL, the content is directly served from the CDN node, if the content exists. Otherwise, the content will be retrieved from the content origin and stored at the CDN node for future requests.

Using CDN has two major benefits. First, because content is served directly from the CDN node that is closest to the user, user experience can be greatly improved. Second, because a large portion of requests will be served from CDN nodes instead of from the original service nodes, the loads on the original service nodes are greatly reduced, making it possible for the service to scale-out to support a much greater number of users.

CDN is used mostly to cache static contents. However, you can cache dynamic outputs from your websites and cloud services as well because CDN content is identified by URLs, including the query parameters. For example, http://<identifier>.vo.msecnd.net/chart.aspx?item=1 and http://<identifier>.vo.msecnd.net/chart.aspx?item=2 represent two different cached objects. You need to be careful not to cache volatile data in CDN, because doing so can adversely affect your performance or even cause content problems, all at increased cost.

Objective summary

  • Traffic Manager can distribute user traffic based on availability and performance.
  • Traffic Manager uses the round-robin, performance, or failover method to decide to which endpoint to route traffic.
  • CDNs serve cached content directly from CDN nodes that are closest to end users.
  • CDNs can reduce traffic to original service nodes by serving static content directly.

Objective review

Answer the following questions to test your knowledge of the information in this objective. You can find the answers to these questions and explanations of why each answer choice is correct or incorrect in the “Answers” section at the end of this chapter.

  1. Which of the following are methods Traffic Manager uses to pick endpoints?

    1. Round-robin
    2. Failover
    3. Performance
    4. Random
  2. What are the benefits of using a CDN?

    1. Reduce response time
    2. Reduce traffic to the original service
    3. Improve data consistency
    4. Enable faster upgrades