Red hat is a subscription based Enterprise Linux OS and is widely recognized secure operating system.

It offers 24/7 support and vendor escalation should any issues arise. According to the Red Hat website, 98% of critical vulnerabilities had fixes within 1 calendar day:
https://www.redhat.com/en/about/trusted
I would highly recommend reading more through the red hat website.

CentOS is a community version of Red Hat operating system. The libraries and binaries are the same and the OS interacts very much the same way however CentOS requires Red Hat to release versions, updates and fixes. Once they are released, they are repackages and released through this OS. There is no vendor escalation although bugs can still be logged, there is no legal obligation to fix these issues. This OS is not subscription based and is a free-to-use OS.

PHP source code is developed and maintained by “The PHP Group”: http://php.net/ . This is made available to vendors (such as RHEL, IUS, Webtatic) who then repackage it for specific Operating Systems. All bug fixes, vulnerabilities etc are fixed by “The PHP Group”.

RedHat and CentOS currently only support 1 php version as its very hard to maintain every version of php. If an issue, bug or vulnerability is found in the supported version then there is a vendor to escalate to (for RHEL, CentOS will then repackage RHELs package after they release).

PHP7 is not part of the RHEL (RedHat Enterprise Linux) packages. This means you need to obtain the relevant versions from other repositories which are “unsupported”. They are unsupported as they are 3rd party community vendors, there is no vendor escalation as with the supported version from RHEL. Bugs can still be logged however there is no time or guarantee it will be fixed. This is because there is no paid support to maintain the packages as such.

Out of all the “unsupported” repositories, IUS is the Rackspace preferred as its generally reliable and is sponsored by Rackspace.

Quoted from the IUS FAQs: https://ius.io/FAQs/

“What is the IUS community project?

The IUS Community Project is an effort to package RPMs of the latest stable versions of the most commonly requested software on Red Hat Enterprise Linux and CentOS. IUS provides a better way to upgrade PHP/MySQL/Python/etc on RHEL or CentOS. The project is run by professional Linux Engineers that are primarily focused on RPM Development in the web hosting industry. What is it NOT?

For one, IUS is not a service of Rackspace but rather is sponsored by Rackspace. Additionally, IUS is not the same as Fedora EPEL or similar repositories. EPEL is geared towards adding packages to RHEL, and has strict guidelines that none of their packages replace anything in RHEL. IUS on the other hand is explicitly geared towards providing packages that do replace existing software in RHEL. Essentially, we are offering a proper way to upgrade software on RHEL when you really need it the latest upstream versions of software.”