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O'Reilly's Performance Optimizations in a Cloud-Centric World

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presents many of the same challenges that we'll explore in the next section—they're often amplified by the challenges of the last mile. 2. Backbone Connectivity Traditionally, this is seen as the path that the data from your website takes after it leaves your data center until it arrives at the end user's machine. However, in the Internet age, backbone connectivity can be seen more as the means by which a user reaches your data—you have little control over how or from where the user is coming to you to request it. Users are now accessing data from an expanding range of devices, via many different means of connectivity, and from an ever- widening range of locations. To understand the performance challenges caused by unknown means of connectivity, you need to look at three key factors: Bandwidth Bandwidth is the amount of traffic that can physically pass through the hardware en route to the end destination. Bandwidth can usu‐ ally be increased on demand from your ISP. Contention Contention is the amount of other traffic that is sharing your con‐ nectivity. This will often vary greatly depending on the time of day. Like bandwidth, contention is something that can be minimized on demand from your ISP. Latency Latency is based on the distance that the data has to travel to get from end to end and any other associated delays involved in estab‐ lishing and maintaining a connection. Which Is the Biggest Challenge to Performance? Bandwidth is often discussed as a limiting factor, but in many cases, latency is the killer—bandwidth can be scaled up, but latency is not as easy to address. There is a theoretical minimum latency that will exist based on the physical distance between two places. Optimally configured fiber connections can travel at approximately 1.5× the speed of light. The speed of light is very fast, but there is still a measurable delay when 4 | Chapter 1: Losing Control

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