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System design patterns

Sharding, load balancing, CAP tradeoffs, and scaling patterns — interview and production ready.

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How to Build a Weighted Random Load Balancer in Python

A Python load balancer mock that distributes requests across servers based on configurable weights using a cumulative weighted random selection algorithm.

python how build

Python

import random
from collections import Counter

SERVERS = {
    "server-a": 50,
    "server-b": 30,
    "server-c": 20,
}


def weighted_random_server(servers: dict[str, int]) -> str:
    """Select a server based on its weight (higher weight = more likely)."""
    total_weight = sum(servers.values())
    rand = random.…

13 0 Open

System design patterns medium

How to implement saga orchestration with compensating steps in Python

Orchestrate a distributed transaction across services, rolling back completed steps with compensations when a later step fails.

saga distributed-transactions compensation

Python

class InventoryService:
    def reserve(self, order_id):
        print(f"[Inventory] Reserving stock for order {order_id}")
        return True

    def compensate(self, order_id):
        print(f"[Inventory] Releasing stock for order {order_id}")


class PaymentService:
    def charge(self, order_id):
        print(f…

14 0 Open

System design patterns medium

Implement a Consistent Hash Ring in Python

Build a minimal consistent hash ring with virtual nodes to map keys to servers stably as nodes are added or removed.

consistent-hashing hashing distributed-systems

Python

import hashlib
import bisect


class ConsistentHashRing:
    def __init__(self, nodes=None, replicas=3):
        self.replicas = replicas
        self.ring = {}
        self.sorted_keys = []
        if nodes:
            for node in nodes:
                self.add_node(node)

    def _hash(self, key):
        return i…

15 0 Open

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