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.
The documentation surrounding AWS Aurora reserved instances is a little confusing. One of its main selling points is seamless Multi-AZ replication at the storage level; however, when you purchase reserved instances the Multi-AZ option is fixed at "No". Does this mean you can't run read replicas in another AZ if you're using reserved instances? Will you be charged the on-demand rate for your read replicas?