Distributed Systems Fundamentals

A distributed system is a collection of independent computers that appears as a single system to users. Distributed systems introduce challenges around consistency, coordination, and fault tolerance that do not exist in single-machine systems. This lesson covers consensus, distributed locks, clock synchronisation, and more.

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Why Distributed Systems Are Hard

In a single-machine system:              In a distributed system:

┌──────────────────────┐                  ┌──────┐     ┌──────┐
│  Everything is in    │                  │Node A│ ←?→ │Node B│
│  one place. One      │                  └──┬───┘     └──┬───┘
│  clock. One memory.  │                     │            │
│  One process.        │                     │  Network   │
│  Simple.             │                     │  (unreliable)
└──────────────────────┘                     │            │
                                          ┌──┴───┐     ┌──┴───┐
                                          │Node C│ ←?→ │Node D│
                                          └──────┘     └──────┘

- Messages can be lost, delayed, or reordered
- Nodes can crash and restart at any time
- Clocks are not synchronised
- There is no shared memory

The Eight Fallacies of Distributed Computing