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The APM Server is kept as a separate component for the following reasons:
- It helps keep the agents as light as possible and since the APM Server is a stateless separate component, it can be scaled independently.
- For real-user-monitoring (beta), data is being collected in agents running in browsers. APM Server prevents browsers from interacting directly with Elasticsearch (which poses a security risk), and controls the amount of data flowing into Elasticsearch.
- In cases where Elasticsearch becomes unresponsive, APM Server can buffer data temporarily (configurable) without adding overhead to the agents.
- The APM Server provides a JSON API for agents to use thereby improving compatibility across different versions of agents and the Elastic Stack.