Zookeeper

Solves problem of service coordination. Centralized service for maintaining configuration info, naming

• synchronizes information accross multiple services
• data is replicated over a set of machines
• clients connect to a single replica over TCP
• Reads are local, writes go through a single server (writing is expensive)

Guarantees

• Seqential consistency; acts like a queue
• Atomicity; update either succeeds or fails
• Single Server Image; same view regardless of which server it connects to