1.1 Introduction
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A distributed system is
"... a system in which the failure of a compute you didn't even know existed can render your own computer unsuable" -- Leslie Lamport
... multiple computers communicating via a network
... trying to achieve some task together
Consists of "nodes" (computer, phone, car, robot, ...)
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What make a system distributed?
It's inherently distributed: e.g., sending a message from your mobile phone to your friend's phone
For better reliability: even if one node fails, the system as a whole keeps functioning
For better performance: get data from a nearby node rather than one halfway round the world
Putting data closer to where the people are
To solve bigger problem: e.g. huge amounts of data, can't fit on one machine
Why NOT make a system distributed?
The trouble with distributed systems
Communication may fail (and we might not even know it has failed)
Processes may crash (and we might not know)
All of this may happen nondeterminisitically
Fault tolerance: we want the system as a whole to continue working, even when some parts are faulty
