When using the `most_free` subnet filter, stuck in the same subnet/availability zone even if spot capacity request fails. about packer-plugin-amazon HOT 1 OPEN

Hi @teddylear,

This looks like a good improvement for the plugin indeed! I've looked into the problem, and I fear that it may not be too trivial to implement at the moment.

The subnet list is not something we do for now, as we choose the VPC/AZ/Subnet prior to booting the instance.
If we want to have fallback combinations, we should rethink the approach, so this becomes a rather large chunk of work and testing to make sure we don't break the user experience.

I tried looking into improving our chances with Spot instances by taking a look at the GetSpotPlacementScores, which we could use as another parameter for picking the VPC/AZ/Subnet, but since we only specify one instance type in the configurations, I failed to see any difference in terms of scoring, and as AWS documents, only specifying one instance always yields low scores, so this may also require changes in order to address this intelligently.

Alternatively, maybe the VPC/Subnet/AZ picking logic does not apply well for Spot instances, and we should rethink our approach for those instance types too.

I'm open to suggestions on this, and if you want to experiment with this, please feel free to do so, we'll gladly review!

from packer-plugin-amazon.