I don't get the trend to split up everything as micro as possible.

Use a proper framework like Symfony (or if, like many people, all you want is a CMS, Drupal) supporting MySQL master-slave or multi-master replication and separation of web frontend and file hosting, host it on AWS (or plain old dedicated servers), put in Cloudflare if you're scared of DDoS kids, and be done. If you need SSO use either provided SSO plugins or an LDAP backend if the SSO is only required for various platforms provided by you.

Said architecture can be built and run on a single server and if you're dealing with spikes you just spin up a couple frontend servers and be done.