say that we have a number of instances on EC2 Classic (without a VPC) and a number of instances within a VPC. The Security Group on the EC2 Classic machines allow TCP only for all the machines within the same SG, which can't be used inside the VPC.

The machines inside the VPC are running a number of workers which have to consume a queue on one of the EC2 Classic instances.

The VPC instances have autoscaling, I can't authorise them one by one on the EC2 Classic SG.

How can I authorise in the EC2 Classic SG my VPC subnet?

Any suggestion would be really helpful.


Put the ASG instances behind your own NAT or an AWS NAT Gateway. Then all of their requests will come from the same IP, making SG rules very simple.

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