Apache Curator is a Java/JVM client library for Apache ZooKeeper, a distributed coordination service. It provides a set of high-level APIs that make it easier to use ZooKeeper for tasks such as distributed configuration management, synchronization, and service discovery.

Pros

• Simplified ZooKeeper API: Curator provides a more intuitive and user-friendly API compared to the native ZooKeeper client, making it easier to work with ZooKeeper.
• Reliability and Stability: Curator is a mature and well-maintained project, with a focus on reliability and stability, making it a popular choice for production use.
• Comprehensive Features: Curator offers a wide range of features, including support for leader election, service discovery, distributed locks, and more, reducing the need for custom implementation.
• Active Community: The Apache Curator project has an active community of contributors and users, providing support, bug fixes, and ongoing development.

Cons

• Complexity: While Curator simplifies the use of ZooKeeper, it can still be complex to set up and configure, especially for newcomers to distributed systems.
• Performance Overhead: The additional abstraction layer provided by Curator may introduce some performance overhead compared to using the native ZooKeeper client directly.
• Dependency on ZooKeeper: Curator is tightly coupled with ZooKeeper, and its usefulness is limited to applications that require a distributed coordination service like ZooKeeper.
• Learning Curve: Developers new to distributed systems and ZooKeeper may face a steeper learning curve when working with Curator.

Code Examples

Distributed Lock Example

CuratorFramework client = CuratorFrameworkFactory.newClient("zookeeper_connection_string", new ExponentialBackoffRetry(1000, 3));
client.start();

InterProcessMutex lock = new InterProcessMutex(client, "/my_lock");
try {
    if (lock.acquire(10, TimeUnit.SECONDS)) {
        try {
            // Perform some critical section of code
        } finally {
            lock.release();
        }
    }
} catch (Exception e) {
    // Handle exceptions
}

This example demonstrates how to use Curator's InterProcessMutex to acquire a distributed lock, perform some critical section of code, and then release the lock.

Service Discovery Example

CuratorFramework client = CuratorFrameworkFactory.newClient("zookeeper_connection_string", new ExponentialBackoffRetry(1000, 3));
client.start();

ServiceDiscovery<InstanceDetails> serviceDiscovery = ServiceDiscoveryBuilder.builder(InstanceDetails.class)
    .basePath("/services")
    .client(client)
    .thisInstance(new InstanceDetails("my-service", "192.168.1.100", 8080))
    .build();
serviceDiscovery.start();

// Discover other service instances
Collection<InstanceDetails> instances = serviceDiscovery.getAllInstances();

This example demonstrates how to use Curator's ServiceDiscovery to register a service instance and discover other instances in the service registry.

Distributed Configuration Example

CuratorFramework client = CuratorFrameworkFactory.newClient("zookeeper_connection_string", new ExponentialBackoffRetry(1000, 3));
client.start();

DistributedConfigurationManager<MyConfig> configManager = DistributedConfigurationBuilder.builder(MyConfig.class)
    .client(client)
    .basePath("/config")
    .build();

// Load the configuration
MyConfig config = configManager.loadConfig();

// Update the configuration
config.setProperty("my.property", "new_value");
configManager.updateConfig(config);

This example demonstrates how to use Curator's DistributedConfigurationManager to load and update a distributed configuration stored in ZooKeeper.

Getting Started

To get started with Apache Curator, follow these steps:

1. Add the Curator dependency to your project's pom.xml file (for Maven-based projects):

<dependency>
    <groupId>org.apache.curator</groupId>
    <artifact