Feature Request: Filesystem adapter

[andrewhowdencom]

Hallo;

This is a stub to track a PR that I hope to write in future. However, I don't know when, or how, so I'm creating an issue to track interest.

I'd like to implement a Filesystem adapter. There are cases where, in shared hosting, I cannot install additional software onto a machine, or the provisioning of such a software would be terribly complex. However, there is access to a semi permanent directory where I can store files associated with an application, such as in the case of Magento, the var directory. Thus, I would like to implement a filesystem adapter that allows reading current metric state and modification thereof from disk.

Although it might be expensive in terms of IO, I would probably write to disk every time a metric incremented rather than batching the metrics in memory and writing them during destruct. The logic is, in some cases destruct may not be reached during abnormal application shutdown, and metrics would be useful for detecting / diagnosing such cases.

If anyone has any thoughts on this, please comment.

See https://github.com/littlemanco/magento-prometheus for implementation.

[andrewhowdencom]

This is WIP here: https://github.com/sitewards/prometheus_client_php/tree/ahowden/add-filesystem-adapter