What makes distributed systems complex?
-heterogeneity
-openness
-security
-scalability
-failure handling
-concurrency
-transparency

DNS - why is it a good example of a distributed system?

Models - client/server, multiple servers, proxies/caches, p2p

Models - synchronous versus asynchronous systems

Failure models - crash, byzantine

Middleware - RPC, distributed objects, marshalling, stub

Web Services - REST/SOAP/XML-RPC, compare to RMI

Clock sync - synch, async, berkeley (internal/external)

Logical time - causal ordering (happened-before), lamport, vector (why use vector instead of lamport?), cuts/global state (consistent, inconsistent)

Failure detection - keep alive messages

Mutual Exclusion - safety/liveness
-central server, token ring, mutlicast and logical clocks

Election - ring, bully

Consensus - possible in sync w/ < 1/3 failure, impossible if communication unreliable, impossible in async

Multicast - building the tree (dense/sparse mode), fault tolerance, FIFO ordering (local seq no), causal ordering (vector timestamps), total ordering (sequencer process)

Replication - passive (one primary), active (mcast to all), lazy (talk to one, it updates others when it can)