Another possible limitation when introducing and scaling microservices is storage. Traditionally, local block devices have been used for storing objects that don't belong to the database (such as static PDF files, documents, or images). Even nowadays, block storage is still very popular with both local block devices and network filesystems such as NFS or CIFS.
While NFS and CIFS are the domain of Network-Attached Storage (NAS), there are also protocols related to a concept operating on a different level: Storage Area Network (SAN). Some of the popular ones are iSCSI, Network Block Device (NBD), ATA over Ethernet, Fibre Channel Protocol, and Fibre Channel over Ethernet.
A different approach features clustered filesystems designed for distributed computing: GlusterFS, CephFS, or Lustre. All of these, however, operate as block devices exposing the same POSIX file API to the user.
A fresh point of view on storage has been proposed as part of Amazon Web Services...