Is this a video course?

No. This is an interactive, slide-based learning platform. Each lesson has rich text, animated diagrams, live code editors, and quizzes. You learn by reading, interacting, and doing, not by watching videos passively.

How long do I have access?

Forever. Both pricing tiers are one-time payments with lifetime access. This includes all current 766 lessons and any future content we add.

What level of experience do I need?

None. We start from absolute basics like 'What is latency?' and build up to distributed consensus protocols. The Foundation level assumes zero prior knowledge of system design.

How much does the system design course cost?

7.99 US dollars for lifetime access globally, or 499 Indian rupees for lifetime access in India. One-time payment, no subscription, no hidden fees. 11 lessons are free with no signup required.

What technologies are covered?

Everything from DNS and load balancers to Kubernetes, Kafka, distributed databases, consensus protocols, stream processing, security architecture, and observability. We cover principles and real-world implementations used at Netflix, Google, Amazon, Uber, Stripe, and more.

Is this useful for system design interview preparation?

Yes. The lessons are structured around the exact topics asked in system design interviews at FAANG and top-tier companies. Interactive diagrams help you practice whiteboard-style explanations. Covers everything from URL shortener design to distributed payment systems.

How is this different from ByteByteGo or Educative?

766 interactive lessons (4x more than most competitors), 16 different diagram types that build step by step, real production examples from Netflix, Google, Amazon, Uber, and Stripe, and lifetime access for a one-time payment of $7.99 instead of annual subscriptions costing 100 to 200 dollars per year.

Why do duplicates occur in at-least-once delivery?

Because if the consumer crashes after processing but before acknowledging, the broker redelivers the unacknowledged message, The broker only knows a message is processed when it receives an ACK. If the consumer processes the message but crashes, loses network, or is slow before ACKing, the broker assumes it wasn't processed and redelivers it. The consumer sees it again: a duplicate.

What is the essential requirement for safely using at-least-once delivery?

The consumer must be idempotent, processing the same message twice must have the same effect as once, Since duplicates are possible (and even expected under failure conditions), consumers must be designed so that processing a message twice produces the same result as processing it once. This property is called idempotency, and it's the safety net that makes at-least-once delivery practical.

Your order processing system uses at-least-once delivery. A message to 'charge $50' is duplicated. What happens if the consumer is NOT idempotent?

The customer is charged $100, the duplicate message triggers a second charge, Without idempotency, the consumer processes the duplicate message as if it's new, charging the customer again. This is exactly why financial operations must implement deduplication, typically by storing a unique transaction ID and checking it before processing.

At-Least-Once Delivery

Name: System Design Masterclass
Availability: InStock

in Messaging Event Systems

This lesson is part of the full System Design Masterclass. Unlock it along with 765 other lessons for a one-time payment.

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Foundation lessons free, try before you buy

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India

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Foundation lessons free, try before you buy

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“The interactive diagrams alone are worth way more than the price.”

Anish K., Senior Engineer at a Bengaluru startup

All 766 interactive lessons

Step-by-step animated diagrams

Live code editors with real execution

Quizzes with instant feedback

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Lifetime access, all future content included

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