amazon-web-services - AWS EC2 Auto Scaling 组 : I get Min and Max, 但所需实例限制是什么？

Question

当您在 AWS EC2 中设置 Auto Scaling 组时，Min 和 Max 界限似乎很有意义:

• 根据政策缩减到的最小实例数
• 根据政策扩展至的最大实例数

但是，我始终无法理解 Desired 到底想要影响什么。

我总是将 Desired 设置为 Min，因为一般来说，我想向 Amazon 支付尽可能少的什一税，除非您需要一个实例来处理负载它应该是 Min 实例数。

我知道，如果您使用 ElasticBeanstalk 并将 Min 设置为 1，将 Max 设置为 2，则会设置 Desired > 到 2(当然!)——您无法为 Desired 选择值。

不同Desired数量的实例的用例是什么以及有何不同？当您期望 AWS 的扩展规模低于您的 Desired(如果您希望的值大于 Min)？

Answer 1

以下是 AWS 支持部门对“最小、期望和最大”值的解释:

MIN: This will be the minimum number of instances that can run in your auto scale group. If your scale down CloudWatch alarm is triggered, your auto scale group will never terminate instances below this number

DESIRED: If you trip a CloudWatch alarm for a scale up event, then it will notify the auto scaler to change it's desired to a specified higher amount and the auto scaler will start an instance/s to meet that number. If you trip a CloudWatch alarm to scale down, then it will change the auto scaler desired to a specified lower number and the auto scaler will terminate instance/s to get to that number.

MAX: This will be the maximum number of instances that you can run in your auto scale group. If your scale up CloudWatch alarm stays triggered, your auto scale group will never create instances more than the maximum amount specified.