Logstash accepts events from different types of sources, processes them (there are tons of inputs, filters and outputs available), converts them to Elasticsearc

Logstash accepts events from different types of sources, processes them (there are tons of inputs, filters and outputs available), converts them to Elasticsearch-compatible format and sends them to the cluster. It is usually used as a central component. For logs and metrics reading, one can use Elastic Beats,such as Filebeat for logfiles. Beats are lightweight agents written in Golang. Recent versions of Elasticsearch also allow to perform the processing step directly in Elasticsearch, using ingest nodes and pipelines (my experience with it wasn't great). In that case Logstash isn't needed.