问题
On cloud services web roles you must create at least 2 instances to get Azure's 99.95% SLA because when they do updates to the servers' OS etc, Azure will need to restart the machines (one at a time). This is well documented and you will be shouted at by the portal when running a one instance web role for doing this.
With Azure websites you don't get such warnings and I cannot find any documentation suggesting 2 instances for the 99.9% SLA. However, I also can't find any documentation saying that you don't need 2 instances for this SLA.
So which is it? Do I need 2 instances for Azure websites' SLA like web roles or is that a thing of the past?
回答1:
A developer on the Azure Websites team has replied here that
the SLA for any Azure Website on the Basic or Standard tier is 99.95%
Just having one instance of the site is enough
回答2:
You can download the Azure Web Sites SLA document here: http://azure.microsoft.com/en-us/support/legal/sla/
It does not state that you need 2 instances to get the 99.9% SLA but clearly state that the Free and Shared Web Site Tiers are not covered by this SLA.
回答3:
We guarantee that Web Apps, Mobile Apps, Logic Apps, and API Apps running in a customer subscription will be available 99.9% of the time, with a 99.95% SLA provided when multiple instances and traffic manager are used. No SLA is provided for Apps or sites under either the Free or Shared tiers.
来源：https://stackoverflow.com/questions/26587234/do-you-need-2-instances-of-azure-websites-for-sla-like-web-roles