Prevent route replacement overwrites in ASG Lambda #169
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norbert
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Right now the ASG Lambda function will always change the routes to the NAT Gateway, when it should only change the routes away from the EC2 instance being terminated.
While there might be some conditions that can lead to severely delayed execution, it doesn't seem to be much of a problem in practice. More importantly, though, the current behavior is wrong when a new instance launches before the function runs as with #167.
There is still an unavoidable race condition between the DescribeRouteTables and ReplaceRoute API calls. When everything is normal there shouldn't be multiple processes changing the route tables concurrently, and in the worst case the current behavior still wins out.