OCI: Yum Reports Error "Could not resolve host: yum$ociregion.$ocidomain; Unknown error"

When trying to install packages on an Oracle Cloud Instance running a custom Oracle Linux image, yum fails with the following error:

# yum -y install net-snmp

Loaded plugins: versionlock

Repository ol7_oci_included is listed more than once in the configuration

https://yum$ociregion.$ocidomain/repo/OracleLinux/OL7/MySQL80_community/x86_64/repodata/repomd.xml:

[Errno 14] curl#6 - "Could not resolve host: yum$ociregion.$ocidomain;

Unknown error"

Trying other mirror.

This error can occur when using a custom image, as some yum variables that normally reside in /etc/yum/vars/* on a standard Oracle Linux OCI image may not exist, such as in the following example: