Azure 计算：操作系统修补、更新和停机
我们知道Azure计算是PaaS，因此操作系统（Windows Server 2008 R2）必须自动修补和升级。
我只是想知道修补或计算升级期间是否会有任何停机时间......？
We know that Azure Compute is PaaS so the Operating System (Windows Server 2008 R2) has to be patched and upgraded automatically.
I just wanted to know will there be any downtime during the patching or Compute upgradation...?
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如果您只有特定虚拟机角色的单个实例，那么是的 - 您将有一小段停机时间，因为您需要重新启动。同样，如果主机操作系统已打补丁，您将需要一段时间的停机时间。
如果您运行两个或更多实例，那么 SLA 就会生效，因为您的实例被分为不同的容器/网络分支/等。这些是故障域。因此，即使某个网段、路由器或整个机架离线，您也会在其他地方拥有另一个实例。
在操作系统更新期间，您的实例将被分为多个升级域，因此它们不会立即全部升级。只要您有两个或多个角色实例，这将使您的服务处于始终可用的状态。对于不面向客户的后台进程（例如，在仅从队列中读取并异步处理队列项的辅助角色中），您可能可以使用该角色的单个实例，前提是您可以处理工作负载并偶尔出现处理延迟是可以接受的。
请参阅最近的 TechNet 博客文章 了解有关故障域和升级域的更多详细信息。
If you only have a single instance of a particular VM role, then yes - you'll have a short bit of downtime, as you need to be rebooted. Likewise, if the host OS is patched, you'll have a bit of downtime.
If you run two or more instances, then the SLA kicks in, because your instances are separated into different containers/network branches/etc. These are fault domains. So even if a network segment, router, or entire rack were to go offline, you'd have another instance somewhere else.
During OS updates, your instances are divided into upgrade domains, so that they're not all upgraded at once. This leaves your service in an always-available state, as long as you have two or more instances of your roles. For background processes that aren't customer-facing (say, in a worker role that simply reads from queues and processes queue items asynchronously), you can probably get away with a single instance of that role, provided you can handle the work load and that it would be ok to have occasional processing delays.
See this recent TechNet blog post for more details around fault domains and upgrade domains.