what's the relationship between iptables and firwalld

I am using RHEL 7. I want to know what’s relationship between firewalld and iptables.

If I want to do some port forwarding, should I use firewall-cmd or iptables ?

when applying rules using iptables, do I need to disable firewalld and install iptables-service ?

I am running a kubenetes cluster, which is booted up with firewalld disabled, If I start firewalld service, I am afraid, It will mess up with kubernetes, as kubernetes already defined many rules.

I want to avoid firewalld, but applying rules with iptables command seems not working, and I can’t install iptables-service too, those nodes have no internet access.

sudo systemctl stop firewalld
sudo systemctl disable firewalld
sudo systemctl mask --now firewalld # to make it impossible for other services to start it