Prometheus exporter for the metrics available in Logstash since version 5.0.

go get -u github.com/lekspyl/logstash_exporter
cd $GOPATH/src/github.com/lekspyl/logstash_exporter
make
./logstash_exporter --web.listen-address=:1234 --logstash.endpoint="https://localhost:1235"

logstash_exporter --help
usage: logstash_exporter [<flags>]

Flags:
  -h, --help              Show context-sensitive help (also try --help-long and
                          --help-man).
      --logstash.endpoint="https://localhost:9600"
                          The protocol, host and port on which logstash metrics
                          API listens
      --web.listen-address=":9198"
                          Address on which to expose metrics and web interface.
      --log.level="info"  Only log messages with the given severity or above.
                          Valid levels: [debug, info, warn, error, fatal]
      --log.format="logger:stderr"
                          Set the log target and format. Example:
                          "logger:syslog?appname=bob&local=7" or
                          "logger:stdout?json=true"
      --version           Show application version.

• logstash_exporter_build_info (gauge)
• logstash_exporter_scrape_duration_seconds: logstash_exporter: Duration of a scrape job. (summary)
• logstash_info_jvm: A metric with a constant '1' value labeled by name, version and vendor of the JVM running Logstash. (counter)
• logstash_info_node: A metric with a constant '1' value labeled by Logstash version. (counter)
• logstash_info_os: A metric with a constant '1' value labeled by name, arch, version and available_processors to the OS running Logstash. (counter)
• logstash_node_gc_collection_duration_seconds_total (counter)
• logstash_node_gc_collection_total (gauge)
• logstash_node_jvm_threads_count (gauge)
• logstash_node_jvm_threads_peak_count (gauge)
• logstash_node_mem_heap_committed_bytes (gauge)
• logstash_node_mem_heap_max_bytes (gauge)
• logstash_node_mem_heap_used_bytes (gauge)
• logstash_node_mem_nonheap_committed_bytes (gauge)
• logstash_node_mem_nonheap_used_bytes (gauge)
• logstash_node_mem_pool_committed_bytes (gauge)
• logstash_node_mem_pool_max_bytes (gauge)
• logstash_node_mem_pool_peak_max_bytes (gauge)
• logstash_node_mem_pool_peak_used_bytes (gauge)
• logstash_node_mem_pool_used_bytes (gauge)
• logstash_node_pipeline_duration_seconds_total (counter)
• logstash_node_pipeline_events_filtered_total (counter)
• logstash_node_pipeline_events_in_total (counter)
• logstash_node_pipeline_events_out_total (counter)
• logstash_node_process_cpu_total_seconds_total (counter)
• logstash_node_process_max_filedescriptors (gauge)
• logstash_node_process_mem_total_virtual_bytes (gauge)
• logstash_node_process_open_filedescriptors (gauge)
• logstash_node_queue_events (counter)
• logstash_node_queue_max_size_bytes (counter)
• logstash_node_queue_max_unread_events: queue_max_ (counter)
• logstash_node_queue_page_capacity_bytes: queue_page_capacity_bytes (counter)