﻿---
title: What is Fleet Server?
description: Fleet Server is a component that connects Elastic Agents to Fleet. It supports many Elastic Agent connections and serves as a control plane for updating...
url: https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/fleet-server
products:
  - Elastic Agent
  - Fleet
applies_to:
  - Elastic Cloud Serverless: Generally available
  - Elastic Stack: Generally available
---

# What is Fleet Server?
Fleet Server is a component that connects Elastic Agents to Fleet. It supports many Elastic Agent connections and serves as a control plane for updating agent policies, collecting status information, and coordinating actions across Elastic Agents. It also provides a scalable architecture. As the size of your agent deployment grows, you can deploy additional Fleet Servers to manage the increased workload.
<admonition title="On-premises Fleet Server" applies-to="Elastic Cloud Serverless: Unavailable">
  On-premises Fleet Server is not currently available for use in an [Elastic Cloud Serverless](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/deploy-manage/deploy/elastic-cloud/serverless) environment. We recommend using the hosted Fleet Server that is included and configured automatically in Serverless Observability and Security projects.
</admonition>

This diagram shows how Elastic Agents communicate with Fleet Server to retrieve agent policies.
![Fleet Server Cloud deployment model](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/images/fleet-server-agent-policies-diagram.png)

1. When a new agent policy is created, the Fleet UI saves the policy to a Fleet index in Elasticsearch.
2. To enroll in the policy, Elastic Agents send a request to Fleet Server, using the enrollment key generated for authentication.
3. Fleet Server monitors Fleet indices, picks up the new agent policy from Elasticsearch, then ships the policy to all Elastic Agents enrolled in that policy. Fleet Server may also write updated policies to the Fleet index to manage coordination between agents.
4. Elastic Agent uses configuration information in the policy to collect and send data to Elasticsearch.
5. Elastic Agent checks in with Fleet Server for updates, maintaining an open connection.
6. When a policy is updated, Fleet Server retrieves the updated policy from Elasticsearch and sends it to the connected Elastic Agents.
7. To communicate with Fleet about the status of Elastic Agents and the policy rollout, Fleet Server writes updates to Fleet indices.

<admonition title="Elastic Agent initiates the connection">
  Elastic Agent always initiates the connection to Fleet Server using an HTTP long polling request to retrieve its configuration.
  - There is no inbound connection from the Fleet Server to the Elastic Agent.
    The Elastic Agent is the client, initiating the communication over HTTP(S).
  - This model supports firewall-friendly architecture and reduces attack surface, as only outbound connections from the Agent need to be allowed.
</admonition>

**Does Fleet Server run inside of Elastic Agent?**
Fleet Server is a subprocess that runs inside a deployed Elastic Agent. This means the deployment steps are similar to any Elastic Agent, except that you enroll the agent in a special Fleet Server policy. Typically—especially in large-scale deployments—this agent is dedicated to running Fleet Server as an Elastic Agent communication host and is not configured for data collection.

## Service account

Fleet Server uses a service token to communicate with Elasticsearch, which contains a `fleet-server` service account. Each Fleet Server can use its own service token, and you can share it across multiple servers (not recommended). The advantage of using a separate token for each server is that you can invalidate each one separately.
You can create a service token by either using the Fleet UI or the Elasticsearch API. For more information, refer to [Deploy Fleet Server on-premises and Elasticsearch on Elastic Cloud](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/add-fleet-server-mixed) or [Deploy on-premises and self-managed Fleet Server](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/add-fleet-server-on-prem), depending on your deployment model.

## Fleet Server high availability

Fleet Server is stateless. Connections to the Fleet Server therefore can be load balanced as long as the Fleet Server has capacity to accept more connections. Load balancing is done on a round-robin basis.
How you handle high availability, fault tolerance, and the lifecycle management of Fleet Server depends on the deployment model you use.

## Learn more

To learn more about deploying and scaling Fleet Server, refer to:
- [Deploy Fleet Server on Elastic Cloud](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/add-fleet-server-cloud)
- [Deploy Fleet Server on-premises and Elasticsearch on Elastic Cloud](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/add-fleet-server-mixed)
- [Deploy on-premises and self-managed Fleet Server](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/add-fleet-server-on-prem)
- [Fleet Server scalability](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/fleet-server-scalability)
- [Monitor a self-managed Fleet Server](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/fleet-server-monitoring)
- [Using a proxy server with Elastic Agent and Fleet](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/fleet-agent-proxy-support)


## Fleet Server secrets configuration

<applies-to>
  - Elastic Cloud Serverless: Unavailable
</applies-to>

Secrets used to configure Fleet Server can either be directly specified in configuration or provided through secret files. Refer to [Fleet Server secrets](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/5314/reference/fleet/fleet-server-secrets) for more information.