How to monitor Apache Kafka metrics?

Before building anything like a microservice, I would explore the kafka exporter for Prometheus to expose Kafka metrics in prometheus format. You could then use Prometheus server to scrape these metrics and Grafana for dashboarding/visualisations. There's other tools you could use for scraping instead of Prometheus/Grafana, e.g. Elastic Metricbeat (which I mention because you've tagged the question with 'elasticsearch'), but the Prometheus/Grafana combination is quite easy to get up and running - there's also out-of-the-box Grafana dashboards that you can install without having to set this up manually e.g. this one.