amazon-web-services - 为 AWS Elastic Load Balancer 指定的公共(public)子网中有 8 个免费 IP 地址？

Question

来自 the relevant section of AWS Official Doc ，规定了以下要求:

When you create a load balancer, you must specify one public subnet from at least two Availability Zones. You can specify only one public subnet per Availability Zone.

To ensure that your load balancer can scale properly, verify that each subnet for your load balancer has a CIDR block with at least a /27 bitmask (for example, 10.0.0.0/27) and has at least 8 free IP addresses. Your load balancer uses these IP addresses to establish connections with the targets.

但是，我不明白为什么——关于需求的一点 8 个免费 IP 地址 .有人可以解释一下吗？提前致谢!

我在互联网上搜索了一下，找不到很好的解释。我认为理解这个要求可能有助于我理解 ELB 的工作原理(我确实阅读了关于“ How ELB works”的章节，但我仍然感到困惑)

Answer 1

AWS Elastic Load Balancers可以向上和向下扩展以满足您网站的流量需求。 scaling up使用您子网中的私有(private) IP 地址。 AWS对它的工作方式不是很满意。我能找到的最好的是对它的模糊引用。

load balancers that all feature the high availability, automatic scaling, and robust security necessary to make your applications fault tolerant

8 free IP addresses下面模糊地解决了，通常它允许 ELB 水平扩展。

If subnets in your VPC run out of available IP addresses, AWS resources, such as load balancers, might not respond successfully to increased traffic.

It's a best practice to keep at least eight IP addresses in each subnet available for use. There are two ways to free up or add additional IP addresses for use with load balancers.

仅供引用，如果您尝试创建一个没有八个免费 IP 地址的 ELB，它将失败，您将收到以下错误消息:

引用

https://aws.amazon.com/elasticloadbalancing/

https://aws.amazon.com/premiumsupport/knowledge-center/subnet-insufficient-ips/