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Apache Zookeeper

Apache Zookeeper. Talentica DevOps Engineering Team. What is distributed system ?. A distributed systems provides single coherent view of collection of independent computing machines. Multiple software components on multiple computers, which run as a single system.

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Apache Zookeeper

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  1. Apache Zookeeper TalenticaDevOps Engineering Team

  2. What is distributed system ? • A distributed systems provides single coherent view of collection of independent computing machines. • Multiple software components on multiple computers, which run as a single system. • It can be locally or geographically connected.

  3. Characteristics of Distributed System • Concurrency • Fault Tolerance • Scalability • Transparency • Heterogeneity

  4. Delusion of Distributed System • Reliable Network • Zero Latency • Infinite Bandwidth • Secure Network • Topology Doesn’t change • Homogeneous Network • There is one administrator

  5. Introducing Zookeeper Zookeeper provides coordination between distributed process via shared hierarchical namespace.

  6. Why Zookeeper ? • Naming Service • Locking • Synchronization • Configuration Management • Leader Election

  7. Zookeeper Architecture

  8. Zookeeper Architecture • Zookeeper follows client server architecture • Collection of Zookeeper servers is called an ensemble • At given time, a Zookeeper client is connected to one Zookeeper server • Client read requests are catered by connected Zookeeper server • Client write requests are forwarded to Zookeeper leader. • Write is considered successful, if quorum is achieved.

  9. Zookeeper Architecture • Client updates are sequentially consistent • Updates are atomic • Updates are reliable • Timeliness

  10. ZAB Protocol • Zookeeper Atomic Broadcast • Propagates state changes from leader to followers • Guarantees the state change

  11. Znodes • Organized similar to standard Unix and Linux file system • Similar to files and directories • Both directory and leaf znode holds data • Stores data <= 1MB

  12. Znode - Hierarchical Namespace

  13. Time in Zookeeper Zxid : Every change to ZK state receives a stamp in form of zxid Version Number : Change to Znode will cause change in Version Ticks : Ticks define timing of events Real Time : To put timestamp of stat structure and znode modification

  14. Znode Stat Structure Czxid : Change that caused Znode to be created Mzxid : Change that last modified Znode Pzxid : Change that last modified children of the Znode Ctime : Millisecond from epoch, when this Znode was created Mtime : Millisecond from epoch, when this Znode was last modified Version : Number of changes to data of Znode Cversion : Number of changes to children of Znode Aversion : Number of changes to ACL of Znode EphemeralOwner : SessionId of owner of this Znode DataLength : Length of data field Numchildren : Number of children

  15. Zookeeper Operations

  16. Zookeeper Operations

  17. Types of Znodes • Ephemeral Znode : Deleted with termination of client session, also can’t have any child znode. • Persistent Znode : Can have child znode, It is explicitly required to delete it. • Sequential Znode : Append a monotonicly increasing counter to the end of path. It is unique to parent znode.

  18. Znode Watchers • One time triggers • Sent to client which sets the watch • Maintained locally at zookeeper • Client won’t receive watches after getting disconnected • Two lists of watches • Data watches : create(),setData(), delete() • Child watches : create(), delete()

  19. Zookeeper ACL • ACL Permission • Create • Read • Write • Delete • Admin

  20. Zookeeper ACL • ACL Scheme • World • Auth • Digest • Host • IP

  21. Zookeeper Recipes/Higher Order Functions/Apache Curator • Naming Service • Service Discovery • Configuration Management • Locks • 2-phase commit • Leader Election • Barriers • Queues

  22. Netflix/SoabaseExhibitor • Zookeeper server is fail fast • Zookeeper is self-healing, (i.e. crashed/failed server if brought online, will automatically join the cluster) • Instance Monitoring • Log Cleanup • Backup/Restore • Cluster-wide configuration • Rolling Ensemble Change • Rich REST API

  23. Backup/Exhibitor • Online Backup - Use Netflix Exhibitor • Offline Backup - Bring down the old ensemble cluster and copy the zookeeper data directory to the new ensemble cluster

  24. Zookeeper Monitoring • 4 Letter Words • JMX

  25. Zookeeper Monitoring - 4 Letter Words

  26. Zookeeper Monitoring - JMX • Mbeans

  27. Data Directory Cleanup • autopurge.snapRetainCount: Maintains n number of recent snapshots along with transaction log • autopurge.purgeInterval : TimeInterval at which purge event will trigger

  28. Zookeeper Future Releases - 3.5.X • Dynamic Reconfiguration w/o Rolling restarts • Separate Dynamic configuration file • Adding/Removing Servers • Modifying server parameters • Rebalance Client Connections • Backward Compatible • Modifying Server Roles[Obersver/Participants]

  29. Zookeeper in Real World • Apache Kafka • Apache Storm • Apache HBase • Apache Solr • Apache Mesos • Apache Hive

  30. Questions ? Thank You

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