Jaeger

Every request that crosses your services can be followed with Jaeger, which records the path as a trace of spans carrying timings, tags and errors. Clients for Go, Java, Node.js and Python report spans over standard protocols, the interface draws service maps and latency waterfalls, and storage can be memory, Cassandra or Elasticsearch.

Developers reach for it when one log line cannot explain why a request took four seconds across a dozen components.

Keeping it on your own servers means the trace data, which can reveal service topology and user identifiers, stays internal, with no vendor quota on span volume and no pricing that grows with traffic.