Evaluation of TinyURL's Design

Reviewing the requirements

The last stage of a system design is to evaluate it as per the non-functional requirements mentioned initially. Let’s look at each metric one by one.

Availability

We need high availability for users generating new short URLs and redirecting them based on the existing short URLs.

Most of our building blocks, like databases, caches, and application servers have built-in replication that ensures availability and fault tolerance. The short URL generation system will not impact the availability either, as it depends on an easily replicable database of available and used unique IDs.

To handle disasters, we can perform frequent backups of the storage and application servers, preferably twice a day, as we can’t risk losing URLs data. We can use the Amazon S3 storage service for backups, as it facilitates cross-zonal replicating and restoration as well. In the worst-case scenario, we might lose 3.3 Million (with 6.6 Million daily requests assumed) newly generated short URLs that are not backed up on that specific day.

Our design uses global server load balancing (GSLB) to handle our system traffic. It ensures intelligent request distribution among different global servers, especially in the case of on-site failures.

We also apply a limit on the requests from clients to secure the intrinsic points of failures. To protect the system against DoS attacks, we use rate limiters between the client and web servers to limit each user’s resource allocation. This will ensure a good and smooth traffic influx and mitigate the exploitation of system resources.