Logging & Monitoring on multiple servers
Well, I spent hours reading lots of articles, documentation, and finally figured everything out. See the comparative table:


Brief description
Zabbix is a full-fledged technology that can deal with both metrics and logs processing, yet can be extended. It also supports automatic hosts detection &amp; network maps building.
Prometheus is a metrics monitoring system. It is Kubernetes native, thus it can automatically detect hosts for data extracting. It also has myriads of available adapters: docs: Exporters And Integrations. To visualize the data, Grafana is used. Speaking about data storage, Prometheus has its own local system for that, but there are integrations with other technologies for sharding, see docs: Storage.
PLG is a stack for log aggregation. Logs get collected with PromTail, Loki is a core processing engine, and Grafana is used as an interface. Loki has no own storage system, so some other solution is required. It stores data as chunks and indexes, which are usually stored separately docs: Storage. As I understood, PLG has no trigger/notification system, but the data extracting part also can parse logs into metrics and export them into Prometheus, so we get alerts. Also, I met a notice that PromTail doesn't support multiline logs, but FluentD can be used instead as it is more flexible.
ELK / EFK is a technology stack for logs parsing, indexing, searching, so it can perform complex queries. For data extracting, LogStash was originally used, but FluentD is becoming popular.