CentOS

① About package(BIND) support
I am planning to introduce bind 9.9.4 to CentOS 7.4 and operate for 10 years.
Is it possible to keep on applying the security patch provided by CentOS without upgrade of bind until the end of the operation?

② About BIND slave
Is it possible to make slave server of the cache server in order to make the cache server redundant?
Is it a common practice to create two cache servers and set the IP addresses of the two cache servers to /etc/resolv.conf?

The CentOS supplied versions of bind are all 9.9.4 and will most likely be so for the rest of the lifetime of CentOS 7 (not 10 years from now but until 2024 as it was released in 2014). Please see https://access.redhat.com/security/updates/backporting for information on how the package management works in CentOS/RHEL. That means that security updates for it are just a yum update away.