Is there a way to change DHCP config in a subnet to point new instances to a different gateway?
I am looking for a way other than modify user data of EC2 instances or setting it up for every instance by different mechanism. Custom routing in RTB is already in place.
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https://docs.aws.amazon.com/vpc/latest/userguide/DHCPOptionSet.html#ChangingDHCPOptionsofaVPC
DHCP option sets are per VPC. It sounds like your question is geared toward a per-subnet modification? "After you create a DHCP option set, you can associate it with one or more VPCs. You can associate only one DHCP option set with a VPC at a time. If you do not associate a DHCP option set with a VPC, this disables domain name resolution in the VPC."
Can the subnet in question be moved/re-created in a different VPC, as an option?
Hello @Piotr Boetzel,
Attaching a Customized Route Table to a subnet will be the only solution that can be taken from the networking side, where you can modify the 0.0.0.0/0 to the new Default Gateway and that will affect all resources inside this subnet.
Agree with this response. Route table using the "catch-all" 0.0.0.0/0 will define the Default G/W per subnet.
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But the DHCP option set does not contain default gateway. If I understand correctly - new instances coming to live in the particular subnet will always have default GW set to a particular (not configurable) address by DHCP unless modified by user data or otherwise.