(This article is part of a series starting with Back to Basics - Global Load Balancing with Traffic Manager)
In the previous article, we covered how the Internet uses the DNS service to resolve addressing between different data center locations, and in this article, we look at how Traffic Manager implements a Global Load Balancing service. Traffic Manager can work in two different configurations:
- Built-in DNS: Traffic Manager can act as the DNS server
with a local DNS service, using a built-in DNS service - Proxy DNS: Traffic Manager can extend the DNS server, by modifying
the responses that the DNS server sends back, acting as a “DNS Proxy”
Using Traffic Manager with Built-in DNS:
Traffic Manager can act as the DNS server with a local DNS service, and hence have local awareness of datacenter location, health and availability. In this model, Traffic Manager uses a built-in DNS service to act as a local authoritative DNS for the application in each data center.
Using Traffic Manager as a Proxy DNS:
Traffic Manager can extend the DNS server, by modifying the responses that the DNS server sends back, ensuring that only the most appropriate IP addresses are contained in each response. In this model, Traffic Manager acts as a “DNS Proxy” which is easier to deploy without changing existing DNS infrastructures.
Whether using the built-in DNS, or acting as a DNS proxy, Traffic Manager works as follows:
- Traffic Manager receives a DNS request for a domain name. It passes
the request on, either to the built-in DNS server, or to an external DNS server. - The DNS server replies with a round-robin list of the IP addresses
for the domain name. Traffic Manager receives the response from the DNS server. - Traffic Manager checks the domain name that was just looked up. If it is not
configured to load-balance traffic for that name, it just sends the complete
response straight back to the originator. - Otherwise, Traffic Manager decides which datacenter is most suitable for the
user who submitted the DNS request. It removes the IP addresses not in that
datacenter from the response and sends the response back to the originator.
Traffic Manager knows how heavily loaded each datacenter is, because It continually monitors all of the data centers and the traffic being routed to each of them, to check they are functioning and to measure their performance. Traffic Manager also knows the geographic location of each datacenter and each user. It can determine the geographic location of each user in much the same way that you could use caller-ID to find out a telephone user’s phone number, and then look up their country and city code.
This works by inspecting the source IP address of the DNS request to determine the IP address of each user. Traffic Manager GLB contains a comprehensive database (sourced from MaxMind) that maps IP addresses to geographic location so that it can accurately select the closest datacenter each time.
With this information – datacenter availability, load and geographic proximity – Traffic Manager GLB can accurately select the most appropriate datacenter for each user of the service.
Next article:
Global Load Balancing is used by many customers using Traffic Manager Traffic Manager and DNS, to enhance the availability and performance of high profile sites on the Internet, as well as for intranet applications.
This article is part of a series:
1. Back to Basics - Global Load Balancing with Traffic Manager
2. Layman’s Guide to Global Load Balancing
3. Global Load Balancing, DNS and the Internet
4. How does Traffic Manager Global Load Balancing Work?
5. An Insider’s Guide to DNS and Global Load Balancing
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