Prometheus is conceptually simple and easy to operate.
Written in Go
Prometheus is written in Go and the static release binaries are deployable without depending on an external runtime (like the JVM), an interpreter (like Python or Ruby), or shared system libraries.
Each Prometheus server gathers data and evaluates alerting rules independently from any other Prometheus server and only stores data locally without tight clustering or replication.
Simple HA setup
To create a highly available (HA) setup for alerting, you can still run two identically configured Prometheus servers computing the same alerts (the Alertmanager will deduplicate notifications):
Of course large-scale deployments of Prometheus or setups with special needs can still become complex. Prometheus also provides interfaces for solving some of its limitations externally, like durable long-term storage. But the building blocks are simple.