In-Depth Understanding of Clustering: Load Balancing and High Availability

Cloud Technologies
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In-Depth Understanding of Clustering: Load Balancing and High Availability

In a distributed system, clustering is a crucial concept that enables the management of multiple instances of services. This article delves into the world of clustering, focusing on load balancing and high availability strategies.

Cluster Overview

A cluster is a layer in a distributed system that deals with the management of multiple instances of services. It’s a complex distributed environment where each service has multiple instances, making service management a challenging task. The Cluster layer is responsible for resolving this issue.

Load Balancing

Load balancing is a critical aspect of clustering, ensuring that the workload is distributed evenly across multiple instances of services. It’s a common misconception that load balancing is only relevant to server load balancing. However, client load balancing is also a crucial aspect of load balancing.

Load Balancing Interface Analysis

The LoadBalance interface is the core of load balancing in a cluster. It’s responsible for selecting the best instance of a service to handle a request.

@Spi (scope = Scope.PROTOTYPE)
public interface LoadBalance <T> {
    void onRefresh (List <Referer <T >> referers);
    Referer <T> select (Request request); // <1>
    void selectToHolder (Request request, List <Referer <T >> refersHolder);
    void setWeightString (String weightString);
}

Load Balancing Algorithms

There are several classic load balancing algorithms, each with its own strengths and weaknesses. Some of the most common load balancing algorithms include:

  • Polling (Round Robin)
  • Weighted Round Robin (Weight Round Robin)
  • Random (Random)
  • Weighted Random (Weight Random)
  • Source Address Hash (Hash)
  • Consistent Hashing (ConsistentHash)
  • Minimum Number of Connections (Least Connections)
  • Concurrent Low Priority (Active Weight)

Each implementation framework supports a different set of load balancing algorithms.

High Availability Strategies

High availability strategies are designed to ensure that a service remains available even in the event of failures. Some common high availability strategies include:

  • Failover (failover): When a failure occurs, retry another server.
  • Rapid Failure (failfast): Only launch a call failed error immediately.
  • Fail-Safe (failsafe): When an exception occurs, ignore it and record the failure.
  • Automatic Failure Recovery (failback): Background record request failed, and retransmit the request after a certain period.
  • Parallel Call (forking): I.e., as long as a successful return, normally used for real-time requirements of high reading operation.
  • Broadcast (broadcast): Radio call-by-call to all providers, Renyiyitai error is an error.

High Availability Interface Analysis

The HaStrategy interface is the core of high availability in a cluster. It’s responsible for implementing high availability strategies.

@Spi (scope = Scope.PROTOTYPE)
public interface HaStrategy <T> {
    void setUrl (URL url);
    Response call (Request request, LoadBalance <T> loadBalance); // <1>
}

High Availability Strategies Implementation

Motan provides two high availability strategies: failfast and failover. The failfast strategy is simple and only selects a load balancing node and initiates the call. The failover strategy is more complex and tolerates failures by retrying a certain number of times.

Other Cluster-Related Knowledge

Dubbo also has a hierarchical cluster structure, which includes a route (Router) used for separate read and write, application isolation, and merge results (Merger) used for the packet in response to the result of the polymerization. Integrates server load balancing Zuul does in SpringCloud-Netflix.

Reference Material

Several simple load balancing algorithms and their Java code implementation are discussed in the article. Search business and technical presentations and fault tolerance are also covered.

Conclusion

In conclusion, load balancing and high availability are critical aspects of clustering in a distributed system. Understanding these concepts and implementing them correctly is essential for ensuring the availability and scalability of a service.