Add regions parameter in aws module config

[kaiyan-sheng]

This PR is to add regions in config for aws module. With regions, we give users the ability to specify what are the regions they want to collect cloudwatch metrics from for different AWS services. regions is optional, when there is no regions in the config, the code will get a full list of AWS regions and loop through all of them.

Please see #11932 for more details.

[kaiyan-sheng]

One concern I have is, will the change consider a breaking change? If so, we can keep the original config default_region and add regions on top of that.

[exekias]

This is a breaking change, IMHO it should be ok because we offer a new way to configure it. In any case it should be also added to the breaking changes list in the changelog

[jsoriano]

This is a breaking change, IMHO it should be ok because we offer a new way to configure it. In any case it should be also added to the breaking changes list in the changelog

Could we keep the old option for backwards compatibility as a synonym of setting regions to a single value?

[exekias]

@kaiyan-sheng to comment here, but If I understood this correctly, default_region was something different from setting a single region. Default region is only used to get the list of regions, we then iterate over them to fetch metrics.

It's more about initialization. I guess it's not a very important setting, although it may be needed in some cases, hence the fallback to take the first region from the list?

[kaiyan-sheng]

@kaiyan-sheng to comment here, but If I understood this correctly, default_region was something different from setting a single region. Default region is only used to get the list of regions, we then iterate over them to fetch metrics.

It's more about initialization. I guess it's not a very important setting, although it may be needed in some cases, hence the fallback to take the first region from the list?

@exekias Yes, default_region is an optional parameter in config currently and it's only for getting the full list of regions from AWS. It just need a value to start the first AWS query and it doesn't matter which region it's default to. But we do need a default value before DescribeRegions API call can be made.

[kaiyan-sheng]

This is a breaking change, IMHO it should be ok because we offer a new way to configure it. In any case it should be also added to the breaking changes list in the changelog

Could we keep the old option for backwards compatibility as a synonym of setting regions to a single value?

@jsoriano Do you mean keep default_region in the config and if user set default_region, then only collect metrics from that default_region? That's also a changing behavior from previous version hmmm

[kaiyan-sheng]

jenkins, test this please

[jsoriano]

This is a breaking change, IMHO it should be ok because we offer a new way to configure it. In any case it should be also added to the breaking changes list in the changelog

Could we keep the old option for backwards compatibility as a synonym of setting regions to a single value?

@jsoriano Do you mean keep default_region in the config and if user set default_region, then only collect metrics from that default_region? That's also a changing behavior from previous version hmmm

I misinterpreted default_region. I wanted to ask if keeping both options is a possibility, so we don't introduce a breaking change.
Now, understanding better default_region, we may still want to keep it to select a region to do this first API call.

[kaiyan-sheng]

@exekias @jsoriano I added default_region back to the config and moved changelog from breaking changes session to added session. Originally I was thinking to remove default_region completely in the future release. But looking at https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-configure.html, it might be good to keep default_region just to be consistent with aws cli configuration example.