Implement a random fixed-size load balancer

Q: Implement a random fixed-size load balancer

This question evaluates understanding of randomized selection, efficient in-memory data structures, and API/state management for a fixed-capacity load balancer that must support addNode, removeNode, and uniform random routing while handling duplicates, removals, and empty-state behavior.

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Question

Problem: Build a simple load balancer

Implement a minimal in-memory load balancer that routes each incoming request to one backend node chosen uniformly at random.

Requirements

The load balancer maintains a set of backend nodes (e.g., strings or IDs).
The number of nodes is bounded by a fixed maximum capacity K .
Support these operations:
1. addNode(nodeId)
  - Adds a node if it is not already present.
  - If the load balancer is at capacity K , define and document what happens (e.g., reject the add / throw).
2. removeNode(nodeId)
  - Removes the node if present; otherwise no-op.
3. route() (or getNodeForRequest() )
  - Returns a node chosen uniformly at random from the currently active nodes.
  - If there are no nodes , define and document what happens (e.g., return null / throw).

Constraints / Edge cases to handle

Adding duplicates.
Removing a non-existent node.
Routing when empty.
Keeping route() efficient (ideally O(1)).

Deliverable

Describe the data structures and implement the API (language-agnostic or Java-style).

Implement a random fixed-size load balancer

Quick Overview

Problem: Build a simple load balancer

Requirements

Constraints / Edge cases to handle

Deliverable

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