Windows Azure cloud computing study note 4-Understanding Fault Tolerant Domain and Upgrade Domain)

According to the Service Level Agreement of Windows Azure, If you deploy two or more examples on different fault tolerant domains and newer domains, windows Azure ensures that your cloud applications can be accessed by the outside within at least 99.95% of the time. Therefore, we need to understand what is a fault-tolerant domain and a new domain.

Fault Domain)

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A fault-tolerant domain represents a physical unit with errors, much like the infrastructure in a data center. Such as a blade machine, but the fault tolerance domain is not one-to-one relationship with the physical computer.

When deploying cloud applications on windows azure, Fabric Controler of Windows Azure is responsible for deploying your applications to different fault tolerant domains, to meet the SLA requirements of windows Azure. To do this, you must configure at least two instances for each Role (Web Role, Worker Role or VM Role.

Upgrade Domain)

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Updating a domain is a logical unit that determines how the Role in an instance performs updates. When an update is required, windows Azure updates the update domain one by one, minimizing the possibility of service unavailability during update failure or update.

When an update request is sent, each Role is notified of the update. Imagine if you have 50 instances ., At the same time, all requests for updates are received. If you update them together, most of the cloud applications will be deleted. Updating the domain is to ensure that they do not perform updates at the same time, so as to ensure service availability.

For example, a cloud service has eight Web role instances and nine Worker Role instances. Windows Azure can distribute these instances to two different update domains.

When the application needs to be updated, first update the instance in domain 1 to get the update notification and perform the update operation. Then, update the instance in domain 2 to continue the external service. After the instances in domain 1 are updated successfully, the instance in domain 2 is updated by the example in domain 1 to provide external services.

The following is the windows Azure application update interface. We cannot control which examples are placed in the new domain. These are automatically completed by Windows Azure.

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