title: ‘Overview’ weight: 1 type: docs aliases:
Stateful Functions' I/O modules allow functions to receive and send messages to external systems. Based on the concept of Ingress (input) and Egress (output) points, and built on top of the Apache Flink® connector ecosystem, I/O modules enable functions to interact with the outside world through the style of message passing.
Commonly used I/O modules are bundled into the runtime by default and can be configured directly via the applications [module configuration]({{< ref “docs/modules/overview” >}}). Additionally, custom connectors for other systems can be [plugged in]({{< ref “docs/modules/io/flink-connectors” >}}) to the runtime.
Remember, to use one of these connectors in an application, third-party components are usually required, e.g., servers for the data stores or message queues.