This document discusses using ThousandEyes to monitor CDN performance. CDNs improve user experience by caching content on distributed servers close to users. ThousandEyes agents can monitor the network paths between servers and users to provide insight into potential issues. The document provides an example of how eBay uses ThousandEyes to monitor key infrastructure like DNS, load balancers, routing and their CDNs to complement real user monitoring.

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CDN Performance Monitoring
Solution Use Case
OVERVIEW
The goal of a CDN network is to optimize application delivery and improve end-user experience.
CDNs achieve this by caching content (e.g. webpages, videos) in many distributed servers placed
close to end-users. That way, when a user tries to access a website serviced by a CDN, the
request will be sent to a cache server near the user. In addition to providing users faster response
times to content, CDNs can also offer load balancing, lower bandwidth costs and deliver higher
availability.
Content delivery networks are generally located in multiple locations around the world, in multiple
networks and potentially serviced by many ISPs. Examples of companies that offer CDN services
are Akamai, Fastly and Cloudflare. Enterprises that have large, geographically dispersed user
bases are among the most likely to leverage a CDN. Nearly a third of the largest websites are
primarily hosted in a CDN, with many more containing CDN-hosted content.
HOW THOUSANDEYES IS RELEVANT
Using ThousandEyes agents to monitor the CDN enterprises can gain insight into potential issues
with upstream ISPs, incorrectly mapped users, overloaded proxy servers, poor page load time or
any other network performance issues affecting the regions monitored. Another key use case of
ThousandEyes is to monitor the difference in application and network performance between a
CDN provider and traditional Data Center hosting.
Reasons to monitor a CDN:
• Prove value: benchmark services, pages or objects before and after the assets are CDN
enabled. Or run ongoing tests both to the edge and origin to compare performance.
• Optimization: ensure the CDN is directing users to the best edge location and is optimizing
the cache to reduce misses and retain freshness.
• Troubleshooting: identify CDN outages, determine which edge is serving requests from
where, find performance issues between the user and the edge, and dig into caching errors.
CUSTOMER USE CASE EXAMPLE
At eBay Marketplace, the e-commerce and auction platform is responsible for matching more
than 24M sellers with 157M buyers. They are hugely reliant on CDNs to serve the tens of billions
of hits per day to eBay receives. Steve Lerner, responsible for Content Delivery Networks (CDN) at
eBay, spoke at a ThousandEyes Connect event, “It’s a big task that means engineering,
operations, vendor management strategy.”
Steve described the importance of network performance to eBay as more than just quantitative
measurements. “It’s not just about packet loss and congestion ... It’s about speed and the things
that are impacting speed itself. We are a retail company and degradation of speed means a
degradation of dollars.”
eBay uses ThousandEyes to monitor key infrastructure components including DNS, load
balancers, routing and CDNs. Steve said, “I like to call ThousandEyes a NOC in a box, a
virtualized NOC of things you used to be doing manually.” eBay uses the synthetic monitoring
ThousandEyes provides to compliment Real User Monitoring (RUM) of the CDN, “Synthetic
monitoring includes it all, presenting a “neutral palette” of indisputable data.”
FAQ
How can I get visibility into the Internet paths where users traffic are distributed?
The path contents traverses between server and user is very different by design when it comes to a
CDN - after all the goal is to distribute that content. Being able to measure the user experience from
many vantage points all over the Internet is critical in understanding how well the CDN is serving a
particular app. ThousandEyes Cloud Agents do exactly this.
How can I validate the SLA between my organization and the CDN provider?
An SLA may be expressed in different ways. Some combination of uptime or availability plus ‘speed’
© Cisco Systems, all rights reserved. Version 2.0. March ’21. Author: Bob P. boporter@cisco.com
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CDX

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Solution Use Case - CDN Performance Monitoring
Page 2
perhaps expressed as time to first byte, or DOM time, full page load, etc. In any case a ThousandEyes
page load test will show will show all of these metrics as well as from where page elements are being
retrieved. This data can be accessed from the ThousandEyes API or rendered into a report and used
to support SLA monitoring needs.
How do I monitor issues with mapping that may affect user experience of the service?
Each vantage point or agent runs a test independently. This can show inconsistencies in mapping or
unexpected or sub-optimal mapping. Since ThousandEyes stores historical data one also is able to
compare ‘now’ and ‘then’ to see what changes affecting user experience have occurred.
How do I ensure constant availability for my relevant sites/apps over the CDN?
In addition to measuring metrics comprising end user experience, the ThousandEyes platform is also
able to alert when metics deviate from the norm thereby facilitating pro-active steps to be keep the
user experience within acceptable limits. Such remediation may be human-led or automated via alerts
feeding into other systems.
ADDITIONAL REFERENCE MATERIAL
• Blog post: An Intro to CDN Monitoring
• Blog post: Optimizing CDN and Web Performance at eBay
• Blog post: Tracking a site’s CDN usage, Powerball example
• Webinar Recording: CDN Monitoring: From Users to Edge to Origin
• Data Sheet: CDN Monitoring Overview
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