How AWS allocate subnet/IP to RDS Oracle Server

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Hi,

When I create an RDS, if I did not select a subnet group and use default AWS seems to associate the RDS with all the subnets in the VPC.

Does this mean that AWS can select any of the subnets to place the RDS oracle server and assign it an IP from the subnet IP assigned range?

Does AWS keep the RDS into the same subnet forever or it can change the subnet and IP to another subnet in the VPC after reboot?

I am trying to open up firewall rules to access the RDs listener port and see if it has to be for all subnets IP ranges or just one subnet.

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According to https://repost.aws/knowledge-center/rds-ip-address-issues you can't guarantee that the IP address will never change.

Because the IP address of your instance is dynamic, you can't assign a static IP address or an Elastic IP address to your instance.

If you want a static IP for your firewall rules you can put a load balancer in front of the RDS instance, as described in https://aws.amazon.com/blogs/database/how-to-use-amazon-rds-and-amazon-aurora-with-a-static-ip-address/

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Steve_M
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  • Exellent Information! However, still not clear on this When you create the RDS, does AWS select randomly any of the default subnets created in the VPC and place the RDS in that subnet? Also, if you reboot or restart the RDS does it keep the RDS always in that same SUBNET that was associated with it when it created it or it can change the subnet?

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selection of RDS DB subnet group will remain as long as you change the subnet through back and restore. AWS doesnt change your subnet in any circumstances.

As mentioned above, your IP address may change, hence is recommended to use the Endpoint name in your configuration while connecting to RDS instances.

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  • The firewall group cannot use Endpoints and need an IP range for destination. When they created the RDS there was no subnet group selection, they used the default VPC subnets and that is why there are 12 subnets associated with RDS. However, I think AWS selects one of those and plaec the RDS in it. This is what I am trying to find out. Does it stay in that subnet forever so I can use that specific subnet IP range or not? If I look at the RDS configuration now, I see a lot of subnets listed. I am trying to find out which specific subnet so i can capture the IP range and send it to firewall group.

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