DNS inside Docker returning public AWS IP address

I have a Rancher cluster and an AWS RDS instance inside the same VPC. Resolving the RDS endpoint should return the internal IP inside of the VPC. This appears to work on the Rancher host, but not inside the Docker container created by Rancher on the same host.

Example on a Rancher EC2 host:

rancher@ip-172-31-49-99 ~]$ nslookup xxxx.xxxx.us-east-1.rds.amazonaws.com
Address 1: ip-172-31-0-2.ec2.internal

Name: xxxx.xxxx.us-east-1.rds.amazonaws.com
Address 1: ip-172-31-2-94.ec2.internal

Now from inside a Docker container running on the same host:

[rancher@ip-172-31-49-99 ~]$ docker exec -it 4f0fddcf50c5 sh
/build # cat /etc/resolv.conf
search bloom-api.rancher.internal bloom-api.bloom-api.rancher.internal rancher.internal
/build # nslookup xxxx.xxxx.us-east-1.rds.amazonaws.com
nslookup: can’t resolve ‘(null)’: Name does not resolve

Name: xxxx.xxxx.us-east-1.rds.amazonaws.com
Address 1: ec2-52-22-86-198.compute-1.amazonaws.com

Why is it returning the public IP (52.xxx) and not the internal IP (172.xxx)?