After discussion with Google experts, they suggested us to look into an alternative way for server discovery to replace the needs of multicast. (Multicast does not work in GKE if the Firefly server pods are on different nodes).
This will involve modifying Firefly to read the configuration at build time to decide on the library to use for service auto discovery. When it is in k8s environment, other software package may need to be installed. We need to document this in SUIT deployment procedure