本文深入探讨了负载均衡器的工作原理及其实现方式。负载均衡器作为运行时代理，通过横向扩展来平衡工作负载，提高性能和容量。文章还介绍了负载均衡器的不同类型，包括多层网络交换机、专用硬件设备、软件系统和服务代理，并阐述了其关键功能，如非对称分配、工作负载优先级划分和内容感知分配。
Load Balancer
The load balancer mechanism is a runtime agent with logic fundamentally based on the premise of employing horizontal scaling to balance a workload across two or more IT resources to increase performance and capacity beyond what a single IT resource can provide. Beyond simple division of labor algorithms (Figure 1), load balancers can perform a range of specialized runtime workload distribution functions that include:
- Asymmetric Distribution – larger workloads are issued to IT resources with higher processing capacities
- Workload Prioritization – workloads are scheduled, queued, discarded, and distributed workloads according to their priority levels
- Content-Aware Distribution – requests are distributed to different IT resources as dictated by the request content
Figure 1 - A load balancer implemented as a service agent transparently distributes incoming workload request messages across two redundant cloud service implementations, which in turn maximizes performance for the clouds service consumers.
A load balancer is programmed or configured with a set of performance and QoS rules and parameters with the general objectives of optimizing IT resource usage, avoiding overloads, and maximizing throughput.
The load balancer mechanisms can exist as a:
- multi-layer network switch
- dedicated hardware appliance
- dedicated software-based system (common in server operating systems)
- service agent (usually controlled by cloud management software)
The load balancer is typically located on the communication path between the IT resources generating the workload and the IT resources performing the workload processing. This mechanism can be designed as a transparent agent that remains hidden from the cloud service consumers, or as a proxy component that abstracts the IT resources performing their workload.
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