# Notes on Distributed Systems 3rd edition (2017)
Book Site: https://www.distributed-systems.net/index.php/books/distributed-systems-3rd-edition-2017/

## What is this?
My personal notes for self-studying this book 🌝

## Ch 1 - Introduction

### Notes
* What is a distributed system?
> A distributed system is a collection of autonomous computing elements that appears to its users as a single coherent system

* Individual computing element in a system is called a **node**
* Nodes can act independently (but probably shouldn't completely ignore each other)
* Each node will have its own concept of time -- cannot assume there is a **global clock**
* Need to be able to manage what nodes are able to join the **group**
* **open group** any node can join the distributed system
* **closed group** access to join the system is restricted and only members of the group can communicate with each other
* Dist system often organized as an **overlay network**
* **overlay network** - https://en.wikipedia.org/wiki/Overlay_network
* **structured overlay** -- nodes have well defined structure / set of neighbors
* **unstructured overlay** -- nodes have references to a random subset of other nodes
* overlay network should always be connected -- every node should be able to reach every other node
* Unpacking "appears to its users as a single coherent system"
* Users should not notice that the system they are dealing with is distributed geographically/across many nodes
* A dist sys is "coherent" if it "behaves according to the expectations of its users"

### Summary