Leader election in HLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary goal of a leader election algorithm in distributed systems?

In a distributed system, multiple nodes need to coordinate. What is the main purpose of running a leader election algorithm?

A To randomly assign tasks to all nodes equally

B To select one node as the coordinator to manage shared resources and tasks

C To shut down all nodes except one to save resources

D To encrypt communication between nodes

💡 Hint

Think about why one node needs to be special in coordination.

The leader election algorithm chooses one node as the leader to coordinate tasks and manage shared resources, ensuring orderly operation.

❓ Architecture

intermediate

Which architecture best supports leader election in a distributed system?

You want to design a system where nodes can elect a leader reliably. Which architecture pattern is most suitable?

A Peer-to-peer architecture where nodes communicate equally and elect a leader

B Client-server architecture with no communication between servers

C Centralized architecture with a single master node

D Monolithic architecture with no distribution

💡 Hint

Leader election requires nodes to communicate and agree.

Peer-to-peer architecture allows nodes to communicate and run leader election algorithms to choose a leader dynamically.

❓ scaling

advanced

How does leader election scale when the number of nodes increases significantly?

Consider a leader election algorithm running on 10 nodes versus 10,000 nodes. What is a common challenge as the system scales?

A Leader election becomes unnecessary with more nodes

B Decreased fault tolerance due to fewer nodes

C Increased message overhead and longer election times

D Nodes stop communicating after scaling

💡 Hint

More nodes mean more communication.

As nodes increase, the number of messages exchanged during leader election grows, causing delays and overhead.

❓ tradeoff

advanced

What is a tradeoff when choosing between a leader election algorithm that is fast but less fault-tolerant versus one that is slower but more fault-tolerant?

You must pick a leader election algorithm. One is fast but may fail if some nodes crash. The other is slower but handles failures well. What is the main tradeoff?

A Security versus usability

B Memory usage versus CPU usage

C Network bandwidth versus disk space

D Speed versus reliability in leader selection

💡 Hint

Think about what matters more: quick leader choice or handling failures.

The tradeoff is between how fast the leader is chosen and how well the system tolerates node failures during election.

❓ estimation

expert

Estimate the message complexity of the Bully algorithm for leader election in a system with N nodes.

The Bully algorithm elects a leader by having nodes with higher IDs take over. How many messages are sent in the worst case when there are N nodes?

A O(N^2) messages

B O(N) messages

C O(log N) messages

D O(1) message

💡 Hint

Consider that each node may send messages to many others in the worst case.

The Bully algorithm can cause many messages because nodes send election messages to all nodes with higher IDs, leading to O(N^2) messages in the worst case.