# Asynchronous Mode Support in Nuclio

>**⚠️ Warning:** Technical preview

## Overview

Nuclio now supports asynchronous function invocation within a single worker process.
This feature enhances performance and resource utilization, particularly in use cases where functions handle multiple concurrent requests. It is especially beneficial for I/O-bound operations.
Currently, asynchronous mode is available only for HTTP triggers and the Python runtime.

## Enabling Async Mode

To enable asynchronous mode, set the `spec.triggers.trigger-name.mode` field to `async` in the function's configuration.
Asynchronous mode operates by establishing multiple socket connections between the Nuclio processor and the worker process. By default, Nuclio creates `1000` connections per worker.
This value can be customized using the `spec.triggers.trigger-name.async.maxConnectionsNumber` field.

## Architecture Considerations and Failure Recovery

Architecture description can be found [here](../../concepts/architecture.md).

Async mode is designed to complement, not replace, Nuclio synchronous processing. It should be used only when asynchronous handling aligns with the function’s behavior.
If a blocking operation is executed within an async function, it can block the entire worker process, preventing other requests from being processed.

When `spec.eventTimeout` is configured, any connection that exceeds the timeout is marked for restart. The connection is then closed, and the Nuclio processor attempts to re-establish it.
If the connection cannot be re-established due to a blocking operation or any other problem, the processor retries up to 3 times, with a 30-second timeout for each attempt.
If all retries fail, the worker process is restarted to ensure proper recovery.