Is Azure Traffic manager is reliable for failover? what are other problems I should be worried about?

Question

I am planning to use Azure Traffic manager to do a failover of my app running on one Azure zone to Azure zone. I need some suggestion, if that is the correct approach to do a failover ? We have seen issue with Azure that, most of the services in one region goes down for few hours. Although I understand that Azure traffic manager is not associated with the region. But is it possible that Azure traffic manager goes down or that traffic manager endpoint is not reachable although my backend webapp is reachable?

If I am planning to use Azure traffic manager, what are other problems I should be worried about ?

Answer 1

I've been working with TM for some time now, so here are a few issues I haven't seen mentioned before:

• Keep-Alive

If your service allows Keep-Alive, then your DNS entry will be ignored as long as the connection remains open. I've seen some exceptionally odd behavior result from this, including users being stuck on a fallback page since they kept using the connection, causing it to remain open indefinitely. If you have access to IIS Manager, you can force Keep-Alive to be false.

• Browser DNS Caching

Most browsers have their own DNS cache, and very few honor DNS Time To Live. In my experience Chrome is pretty responsive, with IE and Edge having significant delays if you need them to rollover quickly. I've heard that Opera is particularly bad.

• Other DNS Caching

Even if you're not accessing your service through a browser, other components can have DNS caches, and some of them will allow you to manage the cache yourself. This can in theory even depend on ISP's DNS caching, though reports on the magnitude of this vary significantly.

Answer 2

Traffic Manager works at the DNS level, which itself is replicated. However, even then, you should still build in redundancy into your solution.

Take a look at the Azure Architecture Center under "Make all things redundant" and you will see a recommendation for Traffic Manager:

consider adding another traffic management solution as a failback. If the Azure Traffic Manager service fails, change your CNAME records in DNS to point to the other traffic management service.