An Introduction to Apache Zookeeper

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Apache Zookeeper

• What is it ?
• How does it work ?
• Problems
• Architecture
• Reliability

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2
Zookeeper What is it ?

• A coordination service
• For distributed systems
• Makes cluster coordination
• Fast
• Scalable
• Runs on a cluster of servers
• Offers pre defined functionality
• No need to re invent the wheel
• Best for read dominant work loads

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3
Zookeeper How does it work ?

• Works via an ensemble of servers
• Clients write changes to ensemble
• Changes processed strictly in order received
• Ensemble selects a leader
• Leader re elected in case of failure
• Designed for small data volumes / meta data

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4
Zookeeper How does it work ?

• Change considered successful if
• It reaches a quorum
• Quorum is at least half of ensemble
• A server will disconnect clients if
• It cant contact quorum within a given time
• Cluster will function if half of servers up
• When a failed server re starts it will
• Re sync with the ensemble

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5
Distributed System Problems

• What type of problems do distributed systems
  encounter
• Inconsistency
• Configuration inconsistencies across cluster
• Race conditions
• Unexpected behaviour due to timing of events
• Dead locks
• Contention for resources

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6
Zookeeper Name Space

• Zookeeper nodes use a hierarchical name space
• Like a file system but for low data volumes
• Path elements separated by a slash ( / )
• Every node in name space identified by a path

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7
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