Question: Problem:

* I have 10 cells (A1-A10) in my workbook where I can enter values. The values are not sorted (always random).
* I have 1 cell (C4) where the average of that value is calculated with the formula: `=AVERAGEIF(A1:10,"<>0")`
* I need a formula for the cell C5 where this average is rounded to a **lower** step value (unless its already equal to one of the step values).
* My step values are:
1,0
1,3
1,7
2,0
2,3
2,7
3,0
3,3
3,7
4,0

Examples:

* If my average value (C4) is 3,2 I need it to show in the field C5 as 3,0.
* If my average value (C4) is 1,3 it needs to stay 1,3

Answer: 
While you can have multiple NAT instances inside a single AZ, each routing table (associated with a subnet) can only have a single entry for the route `0.0.0.0/0`.

The HA approach is normally to have 2 NAT instances (one active, the other one on standby), which check each other. If the standby instance cannot reach the active one, it will replace the other instance's ENI on the `0.0.0.0/0` routing entry.
The two standard patterns for High Availability NAT are:

* [High Availability for Amazon VPC NAT Instances: An Example](https://aws.amazon.com/articles/2781451301784570)
* [Using Squid Proxy Instances for Web Service Access in Amazon VPC: An Example](https://aws.amazon.com/articles/5995712515781075) (Uses proxies instead of route tables, I think)

If you are using the NAT for traffic to Amazon S3, you can also take advantage of [VPC Endpoint for S3](https://aws.amazon.com/blogs/aws/new-vpc-endpoint-for-amazon-s3/) to reduce the reliance on having a HA NAT.