To achieve high availability you can place multiple instances of APM Server behind a regular HTTP load balancer, for example HAProxy or Nginx.

The endpoint / always returns an HTTP 200. You can configure your load balancer to send HTTP requests to this endpoint to determine if an APM Server is running. See APM Server information API for more information on that endpoint.

In case of temporal issues, like unavailable Elasticsearch or a sudden high workload, APM Server does not have an internal queue to buffer requests, but instead leverages an HTTP request timeout to act as back-pressure.

If Elasticsearch goes down, the APM Server will eventually deny incoming requests. Both the APM Server and APM agent(s) will issue logs accordingly.