Assign AZs to a VPC/Subnet

[moofish32]

Separating from: #996 (comment)

As a VPC designer I would like to be able to assign a specific subset of availability zones to a VPC. This is specifically helpful in us-east-1.

[eladb]

Can we add a bit of context/motivation here? I.e why would you want to do that?

[rix0rrr]

Two reasons I can think of:

1. There is a particular AZ in us-east-1 which does not have all the features that the other AZs have. For example, it is not possible to start EKS clusters there, and there's probably more.
2. If you're creating multiple VPCs in the same account, you might want to spread out your VPCs over the AZs like (us-east-1a, b, c), (d, e, f), as opposed to not doing this which would lead to the VPCs spreading over (us-east-1a, b, c), (a, b, c)

[rix0rrr]

This is news to me, but important when implementing this ticket:

• The logical -> physical AZ mapping is exposed: https://docs.aws.amazon.com/ram/latest/userguide/working-with-az-ids.html
• In "newer" regions AZs are no longer randomly mapped for each account, so we might want to do randomization at the CDK level.

[rob-gonz]

For additional Context/Motivation:

• For some QA environments I only want 1 instance inside my ASG and I do not want this ASG in 6 AZ's thus increasing my cost 5x more then necessary.

• Even for production, I don't need to be in every AZ. I only want to be in 1, 2, or 3 for some applications that are only for internal purposes.

[rix0rrr]

@rob-gonz, I think your issue might be solved by #1543, unless you want more fine-grained control over placement

[rob-gonz]

Wow, you guys are fast. Additional fine-grained control would just be a 'nice to have' for me at this point. #1543 should solve my issue.

Edit: It solves my issue for production. Is there a parameter I can input to change the default to be '1' AZ for a given stack/ASG/(or other more appropriate construct). e.g. for a QA/Test stack

[rix0rrr]

I'm confused on the ASG requirement.

You can limit the number of AZs in a VPC using the maxAZs property (set it to 1 if you want a cheap VPC).

ASGs will spread over all AZs in the VPC, but you can still create 1 instance even in a VPC with 3 AZs (by setting maxCapacity to 1), so they scale independently.

[rob-gonz]

I must have missed the existence of the maxAZs property.

...you can still create 1 instance even in a VPC with 3 AZs (by setting maxCapacity to 1),

It didn't click for me that maxCapacity was across all AZ's. Somehow I had it stuck in my head that it was per AZ.

Thanks for taking the time to point the above out.

[eladb]

It didn't click for me that maxCapacity was across all AZ's. Somehow I had it stuck in my head that it was per AZ.

Probably worth clarifying in the docs

[SomayaB]

Information on MaxAZs is here. Closing issue.