If you can correctly answer these questions before going through this section, save time by skimming the Exam Alerts in this section and then completing the Cram Quiz at the end of the section.
1. You have implemented autoscaling on both the web and app tier of your three-tier application, but in times of high read requests, the application seems to be performing slowly or even times out. What could you do to make the application more responsive?
2. You have been tasked with deploying a reliable caching solution that can handle multiple different data types and deliver microsecond to millisecond response performance. Which AWS service would you recommend?
3. True or False: To deliver static content to the user in the fastest possible manner, use a web server with lots of memory and utilize server-side caching.
Answers
1. Answer: Implement the read cache to offload the database that seems to be bottlenecking the read requests.
2. Answer: ElastiCache Redis would support all the required features.
3. Answer: False. Static content should be delivered via a content delivery network (CDN). In AWS, you can use CloudFront to deliver static content through more than 200 geographically distributed locations across the globe.
Now that you have seen how to create an application that is highly scalable and elastic, you need to also consider the scaling impact on the persistent layer. As mentioned in the previous section, you need to consider the scalability of the persistent layer and include it in the overall assessment of the elasticity of the application. It serves no purpose to make an application highly elastic when the database back end is rigid and introduces a bottleneck for the whole application.
This is where caching comes in as a good way to ensure the data in the application is accessible in the fastest manner possible. When delivering an application from the cloud, you can use several different caching strategies to deliver and reuse frequently used data and offload the need to request the same data over and over again.
A simple analogy to caching is your refrigerator. It takes a minute for you to walk to the fridge (the cache) and grab some milk (cache hit). However, when there is no milk (cache miss) in the fridge, you need to go to the store (the origin), grab a few cartons, and take them home to put them in the fridge. The journey to the store and back is many times longer, so it makes sense to buy items that you frequently use and put them in the fridge. The fridge does have a limited capacity, just like cache usually does, and you will typically find a much greater variety of items at the store.
There are several different types of caching that you can use in your application.
When a client requests the contents of the application from a server, you should ensure that components that are static or change infrequently are reused with client-side caching. Modern browsers have this capability built in, and you can use it by specifying cache control headers within your web server or the service that delivers the content, such as S3.
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