Shulou(Shulou.com)06/01 Report--

High availability can be achieved at the following levels:

1 High availability of application layer: for example, the cluster that implements mysql and oracle database applications is mainly to judge whether the mysql and oracle applications stop running.

2 operating system high availability: such as failover clustering (windows failover clusteringWFC) of windows.

3 High availability of the virtualization layer, such as vsphere high availability (HA) and vsphere faulttolerance (FT).

4 High availability of physical layer, such as multiple network adapters, SAN, etc.

The vSphere HA and Fault Tolerance (FT) functions minimize or eliminate unplanned downtime by providing rapid recovery from outages and continuous availability, respectively.

With vSphere, enterprises can easily raise the benchmark level provided for all applications and achieve higher levels of availability at lower cost and simpler operations. With vSphere, you can:

A provides higher availability independent of hardware, operating systems, and applications.

B reduce the planned downtime of common maintenance operations.

C provide automatic recovery in the event of a failure.

1. VSphere HA provides fast interrupt recovery

VSphere HA leverages multiple ESXi hosts configured as clusters to provide fast outage recovery and cost-effective high availability for applications running in virtual machines.

VSphere HA protects application availability in the following ways:

1 prevent server failures by restarting the virtual machine on other hosts in the cluster.

2 prevent application failure by continuously monitoring the virtual machine (sending detection signals to the virtual machine by the host through vmware tools) and resetting it when a fault is detected.

Unlike other clustering solutions, vSphere HA provides the infrastructure and uses it to protect all workloads:

A there is no need to install special software in the application or virtual machine. All workloads are protected by vSphere HA. Once vSphere HA is configured, no action is required to protect the new virtual machine. They are automatically protected.

B vSphere HA can be used in conjunction with vSphere Distributed Resource Scheduler (DRS) to prevent failures and to provide load balancing between hosts within the cluster.

Compared to traditional failover solutions, vSphere HA has several advantages:

Minimize settin

After the vSphere HA cluster is set up, all virtual machines in the cluster can receive failover support without additional configuration.

Reduced hardware costs and settings

Virtual machines can act as mobile containers for applications and can move between hosts. Administrators avoid repetitive configuration on multiple computers. "when using vSphere HA, you must have sufficient resources to fail over the number of hosts to be protected by vSphere HA." However, the vCenter Server system automatically manages resources and configures the cluster.

Improved availability of the application

The availability of any application running within the virtual machine becomes higher. Virtual machines can recover from hardware failures and prevent client operating systems from crashing by monitoring and responding to VMwareTools detection signals and restarting unresponsive virtual machines.

Integration of DRS and vMotion

"if the host fails and the virtual machine is restarted on another host, DRS recommends migration or migrates the virtual machine to balance resource allocation."

VSphere HA clusters allow collections of ESXi hosts to work together as a group, and these hosts provide a higher level of availability to virtual machines than ESXi hosts provide separately.

The hosts in the cluster are monitored, and in the event of a failure, the virtual machine on the failed host is restarted on the standby host.

When creating a vSphere HA cluster, you can choose to use a single host as the preferred host (master) to communicate with the vCenterServer and monitor the status of other hosts, slave hosts (slave), and their virtual machines.

If vSphere HA is enabled for the cluster, all active hosts (hosts that are not in standby or maintenance mode or hosts that are not disconnected) will participate in the election to select the preferred host for the cluster. Hosts that mount the largest number of data stores have an advantage in the election. There is only one preferred host per cluster, and all other hosts are secondary hosts. If the preferred host fails, shuts down, or is removed from the cluster, a new election will take place.

The preferred host in the cluster has many responsibilities:

1 monitor the status of the slave host. If the secondary host fails or cannot be accessed, the preferred host determines the virtual machine that needs to be restarted.

2 monitor the power status of all protected virtual machines. If a virtual machine fails, the preferred host ensures that the virtual machine is restarted. Using the locally placed engine, the preferred host can also determine where to perform the reboot.

3 preferred hosts manage the list of cluster hosts and protected virtual machines and manage hosts that add or remove hosts inside the cluster, that is, the preferred host maintains the inventory within the cluster.

4 the preferred host manages the list of protected virtual machines and updates the list each time the user initiates a switch operation. Vcenter server requires that some virtual machines be protected or not protected. That is, when the virtual machine is powered on, the virtual machine is protected, and if the host fails, the virtual machine will be restarted on other hosts. When the virtual machine is powered off, there is no need to protect it.

5 preferred host cache cluster configuration, master host notification and reminder slave host, cluster configuration modification.

6 the master host sends heartbeat information to the slave host to let the slave host know the existence of master. If the slave host does not receive the heartbeat information, the new preferred host is re-elected.

7 master reports status information to vcenter,vcenter normally only communicates with the master host.

One of the preferred functions performed by the host is virtual machine protection. "when a virtual machine is protected, vSphere HA ensures that it attempts to power back on after its failure."

The preferred host is committed to protecting the virtual machine when it is observed that the power condition of the virtual machine has changed from power off to power on.

Machine. In the event of a failover, the preferred host must restart the protected virtual machine for which it is responsible. This responsibility has been assigned to the preferred host that exclusively locks the system definition file on the data store that contains the virtual machine profile.

Responsibilities of slave hosts in the cluster:

1 the slave host monitors the status of locally running virtual machines and sends significant changes in the running status of these virtual machines to the master host.

2 the slave host monitors the health status of the master host. If the master host fails, the slave host participates in the election of the master.

3 slave uses the characteristics of vSphereHA access control vSphereHA, which do not need the coordination of master. These features include VMHealth Monitoring.

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