Detailed component design

API Gateway, load balance:

The API gateway load balancer is critical in the system as we can't afford all traffic to a single server to generate/retrieve urls.

For long url to short url scenario, we could use some hash func to generate hash (MD5, SHA-1) for long url and redirect based on the hash value. To avoid uneven traffic and hot node, we could use consistent hash and virtual nodes to minimize data movement when adding/removing servers.

For short url fetching long url we could load balance based on the last digit of short url. This way, we could divide the traffic to 64 node (short url generated using base64). We could have hot node problem, but from there, we could distribute even further by using the last two digits of the short url.

Database

Another key factor for our short url generation is the auto increment feature of SQL database. This ensures we would generate unique shorturl. A single SQL DB would be a bottleneck for generating urls, to resolve, we could add multiple SQL DBs. And to avoid conflicting short urls, we could give each DB an id, which will be added as prefix to the shorturl. With this mechanism, it also make it easier when we fetch longUrl from shorUrl. The LB could distribute based on the prefix part to correspoding DB cluster first.

Cache

Cache is essential for faster longurl fetching. Based on the above LB approach, we could add cache between each service and DB. The cache is mostly a key value pair in memory cache like Redis/Memcached, store the top visited shorturls and evict based on LRU.

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Displaying Solutions with Scores Ranging from 1 to 10