> For the complete documentation index, see [llms.txt](https://cortex-docs.paloaltonetworks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://cortex-docs.paloaltonetworks.com/cortex-xpanse/active-response/engines/engines-use-case.md).

# Engines Use Case

An engine is used for the following purposes:

* [Engine Proxy](#UUID-27418e4a-1673-165d-45a7-837284307e67_id0f037a25-017e-48e9-a9bf-cadf473f4520)
* [Engine Load-Balancing](#UUID-27418e4a-1673-165d-45a7-837284307e67_idc03241ca-2030-4382-9bd9-e4dfb890a0a3)

**Engine Proxy**

Engines enable to access internal or external services that are otherwise blocked by a firewall or a proxy, etc. For example, if a firewall blocks external communication and you want to run the Rasterize integration, you need to install an engine to access the Internet.

**Engine Architecture**

Within the network, you need to allow the engine to access the Cortex Xpanse’s IP address and listening port (by default, TCP 443). The engine always initiates the communication to Cortex Xpanse.

**Engine Load-Balancing**

Engines can be part of a load-balancing group, which enables distribution of the command execution load. The load-balancing group uses an algorithm to efficiently share the workload for integrations that the group is assigned to, thereby speeding up execution time. In general, heavy workloads are caused by playbooks that run a high number of commands.

Before configuring an integration to run using multiple engines in a load-balancing group, it is recommended that you test the integration using a single engine in the load-balancing group.

{% hint style="info" %}

### Note

When you add an engine to a load balancing group, you cannot use that engine separately. The engine does not appear in the engines drop-down menu when configuring an integration instance.
{% endhint %}


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