Hi @rlinux,
APM is an application for monitoring other application performance. What you mean exactly when you say "only use ELK with APM"?
I'm a bit confused about your desired goals. Please let me know a bit detailed explanation so we can provide you a better assistance.
Logstash is used to format and enrich events before sending them to Elasticsearch.
where they talk about monitoring Logstash component.
If you need help monitoring your Logstash instances I can help you, otherwise, I need more information as I don't understand properly your message.
Regards,
Jesús