AWS X-Ray is an application monitoring tool by Amazon Web Services that allows you to get an insight into how your applications are performing in production. It also allows you to see how your applications interact with each other, with external services, and with some of AWS' own services. All that's required is to add some instrumentation code at key points in your application. Despite lack of official support, it can be used with PHP.
Opcache is one of PHP's most powerful tools when it comes to performance. With the release of PHP 7 it received a new feature which has gone largely un-noticed: the file cache. Depending on your hosting environment and/or traffic levels the file cache may be able to help squeeze even more performance out of PHP.
PHP apps can easily begin to slow down over time as they grow, and with the recent patches for the Meltdown vulnerability adding a performance penalty to many workloads this slowdown can be amplified. Often there are some simple changes that can be made in order to see a measurable performance improvement for production workloads.
If you're working on or debugging a PHP application that creates files in the /tmp directory then you may find yourself needing to check for the existence of or the content of these files. On RHEL/CentOS 6 and below this would be as straightforward as listing the contents of /tmp or opening the file in your preferred text editor. On RHEL/CentOS 7 however you may be surprised to see that while your application can see its files fine, you can't.