Welcome to the Show of CDN Monitoring: Act 3
Things Going Wrong
By: Kristian Skoeld
Dec. 21, 2013 03:00 PM
In my previous two posts Act 1 - The What and Why and Act2 - The How and How Not I covered the main benefits of CDNs and what type of tools are needed to monitor them. Now, I want to go into some detail of why you need to consider monitoring them in the first place. Let's face it: if things work well enough, why worry about monitoring them? Of course it is great to be able to see all the details, but do I really need all that information? Aren't the CDNs doing a good enough job?
The answer to that last one: Yes, CDNs are doing a very good job ... most of the time.
How can you know the CDN delivers what it promised?
Back in my theatre days (see Act 1 - The What and Why) we took the risk and chose our marketing flyer distribution agency purely based on budget and gut feeling. Soon our flyers could be found in relevant tourist and culture locations across Berlin and even all the way in Hamburg. They even gave us the option to replace the material with new versions on short notice (e.g., updating the flyers with a note that the first two shows were sold out already). And believe me, we certainly didn't have the bandwidth to pull such a stunt on our own just a few days before the opening night.
Our theatre "CDN" journey ended there - but think of bigger players like Disneyland or "Phantom of the Opera" that spend a fortune on making sure I see their flyers in all the hotels I visit - they sure seem to follow me wherever I travel.
We were not "professional" enough to actually validate that our investment was a good one - or to even systematically check whether they did everything they told us. Again: we were quite busy running the show. But overall we were quite happy.
And now think of your CDN investment.
What does the CDN promise?
What could possibly go wrong?
However we very often do see issues undetected by traditional testing/monitoring approaches caused by CDN customer misconfigurations, CDN outages or other irregularities.
And again thinking back - all of these issues exist in the real brochure world as well.
While not complete the list includes:
Example 1: CDN requests misrouted across the globe
In these particular examples synthetic tests have been executed using the Compuware APMaaS Last Mile agents from a large number of different locations within Australia, Germany or Italy.
Results show that in many cases PoPs in USA were hit from machines located in Australia and while some of these did offer a very low connection latency, quite a number of them did cause a dramatic slowdown in the overall end-user performance. The table shows the average connect time from the last mile agents to the PoP as a measure of the latency.
1. Avg connection time of 20 most hit CDN PoPs running synthetic last mile tests in Australia
Another example shows that it's not only Australia having such issues. The following map shows results from a test conducted in Germany over 24h. Green dots represent the locations of end-user machines used for the synthetic Last Mile test and the red dots show the locations of the hit CDN PoPs.
2. Request from within Germany are routed to CDN PoPs across the globe
Yet another case found with one of our Italian customers showed that the response times of end users connected with Telecom Italia as their local ISP were 33% above the average of all others. Looking at the network components the biggest difference was the average connection time to the CDN PoPs being used. The end-user machines using Telecom Italia had an average connection time of 298ms while all others connected within 181ms. Drilling into the details we found that most of the CDN PoPs hit by these end-user machines were actually located in the US, which of course explains the drop in performance.
Comparison average CDN PoP connection time Telecom Italia vs other ISPs
CDN PoPs hit from Italy - minimum 100 total connections
Lesson learned: Make sure you know where the content is delivered from and correlate end user performance to increased latency due to mis-routing.
To dive into examples 2-5, click here to read more:
Don't live with the risk of not knowing what is going on with your application. Click here to be sure your CDN Monitoring is being handled correctly!
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