关于AWS的两个问题RDS 多可用区
我了解到，当从单可用区升级到多可用区 rds 时，会发生“breef i/o freeze”。这到底是什么意思？
当升级到多可用区部署时（例如从小到大），生产数据库是否会受到影响？它能够使用备份数据库，然后进行故障转移吗？
I understand that when upgrading to a Multi-AZ rds from a Single-AZ, there occurs a "breef i/o freeze". What exactly does that mean?
When an upgrade is made to a Multi-AZ deployment, say from small to large, will the production database be impacted at all? Will it be able to use the backup databse, then failover?
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您的问题的答案已记录下来：
当您选择从单可用区移动到多可用区时，会发生短暂的 I/O 冻结。这意味着在一段时间内数据库将无法访问。不会对数据库执行任何读、写操作。大多数情况下，此过程的持续时间约为 3-4 分钟。
是的，当您调整计算大小（从小到大）时，生产数据库将会受到影响。执行调整大小操作的最佳方法是在计划的维护时段内。如果选择“立即应用”选项，有时数据库将无法访问（需要将控制权切换到备份服务器）。
问候，
桑克特·丹吉
Answers to your questions are written down :
When you choose to move from Single AZ to Multi AZ, brief I/O freeze happens. It means that for some duration database won't be accessible. No read,write operations will be performed on the database. Mostly, the duration for this is around 3-4 minutes.
Yeah, production database will be affected when you resize the compute(from small to large). The best idea to perform resize operation is during scheduled maintenance window. If select Apply Immediately option, for sometime the database won't be accessible(time to switch control to backup server).
Regards,
Sanket Dangi
从单可用区转换为多可用区时的停机时间本质上是新实例启动并完全发挥作用所需的时间，正如 sanket 所说，可能需要几分钟。
扩展多可用区部署首先扩展从属实例，然后执行故障转移。停机时间是进行实际故障转移所需的时间 - 通常接近一分钟。
扩展多可用区部署是通过添加额外的只读副本（源自备用数据库）来完成的，这不会造成中断。请记住，添加只读副本会创建一个最终一致的系统，这可能是理想的，也可能不是理想的。
同样值得一提的是，您应该在所有多可用区实例中使用相同的实例类型，否则不平衡可能会导致副本延迟。
您可能已经意识到，最好从一开始就采用多可用区配置。它使扩展和扩展变得更加容易，并且停机时间更少。
the downtime when converting from single-AZ to multi-AZ is essentially the time it takes for a new instance to launch and become fully functional as sanket said, it may take a few mins.
scaling up a multi-AZ deployment first scales up the slave instance, then performs a failover. the downtime is the time it takes to do the actual failover - usually closer to a minute.
scaling out a multi-AZ deployment is done by adding additional read-replicas (sourced off of the standby) which incurs no interruption. keep in mind that adding read-replicas creates an eventually consistent system which may or may not be desirable.
it's also worth nothing that you should use the same instance types across all multi-AZ instances, otherwise the imbalance may incur replica lag.
as you're probably realizing, it's best to start with a multi-AZ configuration from the beginning. it makes scaling up and scaling out a lot easier and with less downtime.
问题1仍然有效吗？根据 AWS 文档 (2022)，没有停机时间，但性能略有下降。
引用AWS文档：
Is question 1 still valid? According to AWS documentation (2022) there is no downtime, but there is a small decrease in performance.
Quoting AWS documentation: