Grokking the System Design Interview
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Leader and Follower

When the same data is stored on several machines, those machines can disagree about it. Two users change the same row at the same time, on two different machines, and now there are two different answers.

The simplest way to prevent this is to let only one machine accept changes. That machine is called the leader. The other machines are called followers. They copy the leader's changes and hold the same data.

Database documentation often calls the same two roles the primary and the replicas. The names are different and the idea is the same

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Peter Jeng

Peter Jeng

· 3 years ago

In this article, it states that the quorum is not sufficient enough to solve the availability issue of the system due to its 2/N + 1 constraint of healthy servers.

However, does the leader/follower example work in conjunction with quorums, in that do we still need a certain number of reads/writes (R + W > N) done across the entire system?

According to this article: https://aws.amazon.com/builders-library/leader-election-in-distributed-systems/ it seems that the leader becomes a single source of failure in many aspects.

Also in the diagram posted, the leader handles all read/write request and then distributes the replica request to its follower, but doesn't this become a single source of failure that quoru

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