noc19-cs33 Lec 16 Design of Zookeeper

Introduction

This tutorial covers the design principles of Zookeeper as discussed in the lecture from IIT Kanpur's NPTEL series. Zookeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and group services in a distributed system. Understanding its design is crucial for building reliable and scalable distributed applications.

Step 1: Understand Zookeeper's Role in Distributed Systems

• Zookeeper acts as a coordination service for distributed applications, helping manage configurations and providing synchronization.
• It maintains a hierarchical namespace for storing metadata and configuration information, similar to a filesystem.
• Key components include:
  • ZNodes: Data nodes which can hold data and can be ephemeral or persistent.
  • Sessions: Clients connect to Zookeeper through sessions, which are maintained through heartbeats.

Step 2: Explore the Zookeeper Architecture

• Zookeeper's architecture consists of a cluster of servers (ensemble) that provide high availability.
• The ensemble works through a leader-follower model:
  • One server acts as the leader, handling write requests.
  • Other servers are followers, responding to read requests and replicating data from the leader.
• Important features of the architecture:
  • Atomic Broadcast: Ensures that updates are consistently applied across the ensemble.
  • Watches: Clients can set up watches on nodes, allowing them to be notified of changes.

Step 3: Learn About Zookeeper Operations

• Zookeeper supports a variety of operations:
  • Create: Add a new ZNode.
  • Read: Retrieve data from a ZNode.
  • Update: Modify data stored in a ZNode.
  • Delete: Remove a ZNode.
• Each operation is atomic, meaning it either fully happens or doesn't happen at all, ensuring data integrity.

Step 4: Implement Zookeeper in Applications

• Use Zookeeper for:
  • Configuration management: Store and manage application settings centrally.
  • Leader election: Determine which node will be responsible for a particular task.
  • Distributed locks: Manage access to shared resources among distributed components.
• Example code snippet to connect to Zookeeper:

  from kazoo.client import KazooClient
  
  # Connect to Zookeeper
  zk = KazooClient(hosts='127.0.0.1:2181')
  zk.start()
  
  # Create a ZNode
  zk.create("/my_znode", b"Hello Zookeeper!")
  
  # Read data from ZNode
  data, stat = zk.get("/my_znode")
  print(data.decode("utf-8"))
  
  # Stop the Zookeeper client
  zk.stop()
  

Conclusion

In this tutorial, we explored the design and operations of Zookeeper, a crucial tool for managing distributed systems. Key takeaways include understanding its architecture, operations, and practical applications. For further exploration, consider implementing Zookeeper in a small distributed application to solidify your understanding of its functionalities and benefits.