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hardSystem Design

What is leader election in distributed systems?

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01

Understand the problem

Explain leader election.

leader-election
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

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03

Study the solution

Step 1: Outline use cases and constraints

Gather requirements and scope the problem. Ask questions to clarify use cases and constraints. Discuss assumptions.

Use cases

We'll scope the problem to handle only the following use cases

  • User needs to understand leader-election to make architecture d

Solution ready — 2 min read

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04

Read the code

Majority-vote election (simplified)
Run Playground
class Node:
    def __init__(self, node_id):
        self.id = node_id
        self.term = 0
        self.voted_for = None

def elect(nodes, candidate):
    candidate.term += 1                 # start a new election term
    votes = 1                           # candidate votes for itself
    for n in nodes:
        if n is candidate:
            continue
        if n.term < candidate.term:     # grant vote for a newer term
            n.term = candidate.term
            n.voted_for = candidate.id
            votes += 1
    majority = len(nodes) // 2 + 1
    return votes >= majority, votes

nodes = [Node(i) for i in range(5)]
won, votes = elect(nodes, nodes[0])
print("node 0 won?", won, "with", votes, "/", len(nodes), "votes")
05

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