A URL Shortener

In this chapter, we design a URL shortener for three different systems, and we apply what the course has covered so far to each design decision.

After reading this chapter, you should be able to:

Define URL shortener and short code, and name its two operations, shorten and follow
State each variant’s added functional requirements, quality attributes, and requirements for short codes
Estimate requests per second, the read-to-write ratio, and storage per year from daily numbers
Explain why following a link must be a REST endpoint, and choose between 301 and 302 redirects
Compare relational, document, and key-value databases for the links, and justify a choice
Use the hit ratio to decide which variants need a cache
Explain how invalidation and expiry stop a blocked link from redirecting
Decide which variants need replicas, for reads, for failover, or both
Classify following, creating, and turning off a link as CP or AP during a network partition
Explain why routing by a hash of the code fits the links better than a directory, and what it gives up
Compare ways to generate short codes, and choose one for each variant

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