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In the security groups, assign incoming access to other security
groups by specifying a security group ID instead of IP addresses.
In the web console, if you start typing "sg" in the source field it
will pop up a list of your security groups to choose from.
Using a security group ID as the source allows all resources
that belong to that security group to have access.
Alternatively, if you just want one rule that allows access to
every resource in your VPC you would specify your VPC's IP range.