routing-keepalive.html.md.erb

---
title: Router Back-End Keepalive Connections
owner: Routing
---

<strong><%= modified_date %></strong>

This topic describes how to enable support in Gorouter for keepalive connections with backends, and considerations for configuration.

Support for keepalive connections is described in [Idle Keepalive Connections](../concepts/http-routing.html#keepalive).

## <a id="enable"></a>Enable Keepalive Connections from Gorouter to Backends

By default, support for keepalive connections with backends is disabled. <%= vars.keepalive_router %>

## <a id="max-idle"></a>Considerations for Configuring Max Idle Keepalive Connections

Each router process is limited to 100,000 file descriptors. Each inbound request consumes at most two file descriptors; one for the connection from the client and one from Gorouter to the backend. For this reason we recommend that Max Idle Connections is never set higher than 50,000. As a few other file descriptors are consumed by the process under normal operation, this limit is more like 49,900.

In order to determine how many idle connections are needed, consider that the peak connections could be calculated by multiplying throughput by response time. Example: if a single router receives 1000 requests per second, and response time is 1 second, at any given time there are likely to be 1000 connections open to backends. Accommodating for growth of 2x, an operator might configure a maximum of 2000 idle connections per router.

Gorouter has been hard coded with a limit of 100 idle connections per backend. The configurable property `max_idle_connections` governs idle connections across all backends.