VMware的vSphere集群服务（vCLS）是vSphere 7 Update 1引入的一项关键创新，旨在增强现代IT基础设施的可扩展性和可靠性。vCLS提供了一个分布式且解耦的控制平面，即使vCenter Server发生故障，核心集群服务也能继续运行，从而提高了如分布式资源调度器（DRS）等功能的服务可用性。通过部署轻量级代理虚拟机，vCLS实现了集群服务的自我管理和高可用性，显著提升了虚拟化基础设施的稳定性和效率。

💡vCLS的核心功能是提供一个分布式且解耦的控制平面，用于集群服务。它允许核心集群服务独立于vCenter Server运行，即使vCenter Server发生故障，关键功能如DRS也能继续运作。

⚙️vCLS的架构依赖于在每个vSphere集群内自动部署的轻量级代理虚拟机。每个集群最多创建3个代理虚拟机，构成仲裁以维持服务可用性。在少于3个主机的较小集群中，代理虚拟机的数量与ESXi主机的数量相同。

🖥️这些代理虚拟机采用精简配置，运行Photon OS，占用极少的资源：内存128 MB，vCPU 1个，磁盘2 GB（精简配置），无网络适配器。vCLS会监控并自我管理代理虚拟机的可用性，确保服务完整性。

✅vCLS提供三种健康状态：健康、降级和不健康。当代理虚拟机不可用时，vCLS会自动重新部署或开启它们，以维持服务。管理员无需直接维护或干预这些代理虚拟机，只需遵循相关操作指南，如避免删除、重命名或关闭代理虚拟机。

🚀vCLS显著增强了VMware集群的弹性和可扩展性，通过使基本服务独立于vCenter Server运行来实现。这种创新降低了服务停机的风险，并优化了本地和云环境中的操作。通过利用vCLS，组织可以在其虚拟基础设施中实现更高水平的自动化、稳定性和性能。

VMware continuously enhances its vSphere platform to address scalability and reliability challenges in modern IT infrastructures. One key innovation is the vSphere Clustering Service (vCLS), introduced in vSphere 7 Update 1. Let’s explore how this service improves cluster operations and availability.

What is vCLS?

vCLS provides a distributed and decoupled control plane for clustering services, improving the reliability of features like the Distributed Resource Scheduler (DRS). Traditionally, clustering services depended on the vCenter Server’s availability. This dependency posed limitations on scalability and resilience. With vCLS, these challenges are mitigated, as it allows core clustering services to function even if the vCenter Server experiences downtime.

Architecture and Agent VMs

The vCLS architecture relies on lightweight agent VMs that are deployed automatically within each vSphere cluster. Key points include:

Up to 3 agent VMs per cluster are created, forming a quorum to maintain service availability. In smaller clusters with fewer than 3 hosts, the number of agent VMs matches the number of ESXi hosts. These agent VMs are managed by vSphere and require no manual intervention from administrators.

Each vCLS agent VM runs a minimal configuration with a Photon OS, utilizing minimal resources:

Memory: 128 MB (100 MB reserved) vCPU: 1 (100 MHz reserved) Disk: 2 GB (thin provisioned) No network adapter

Cluster Service Health

vCLS monitors and self-manages the availability of its agent VMs, with three health states:

Healthy: At least one agent VM is active and functional. Degraded: One or more agent VMs are temporarily unavailable, though DRS operations continue. Unhealthy: DRS operations are interrupted due to a lack of available agent VMs.

If any agent VM becomes unavailable, vCLS automatically re-deploys or powers it on to maintain service integrity.

Operational Guidelines

Administrators do not need to maintain or interact with the agent VMs directly. The following practices help ensure smooth operations:

Avoid deleting, renaming, or powering off agent VMs. When placing a host in maintenance mode, the agent VMs are automatically migrated to another host. Agent VMs are visible in the vSphere Client under the vCLS folder, but not in the Hosts and Clusters view.

Automation scripts should be configured to ignore vCLS agent VMs to prevent accidental disruptions. These VMs can be identified using specific properties such as ManagedByInfo.

Why vCLS Matters

vCLS significantly enhances the resilience and scalability of VMware clusters by enabling essential services to function independently of vCenter Server. This innovation reduces service downtime risks and optimizes operations in both on-premises and cloud environments.

By leveraging vCLS, organizations can achieve a higher level of automation, stability, and performance in their virtual infrastructure. VMware’s forward-thinking approach ensures that clusters remain robust and efficient, even under challenging conditions.