Running with Docker image causes 10 second delay in responses

[tomi-bigpi]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

5.6.1

Plugin version

6.3.0

Node.js version

22

Operating system

Linux

Operating system version (i.e. 20.04, 11.3, 10)

public.ecr.aws/lambda/nodejs:22.2025.10.29.20

Description

Just wanted to drop a note and report an issue I ran into using @fastify/aws-lambda when running in a Docker container on Lambda versus a native Node runtime. It seems that the library adds almost exactly 10 seconds to the response time. Primarily logging this in case anyone else runs into it, so feel free to close.

After some debugging, I modified the code to not use the callback function it detects (which I think isn't actually the callback, but possibly some other method - didn't spend too much time tracing that, since the build/test cycle is slow in this flow).

By simply returning the promise on https://github.com/fastify/aws-lambda-fastify/blob/main/index.js#L209 there is no delay in the response.

Somewhat related to #268 .

This is with a Dockerfile starting with:

FROM public.ecr.aws/lambda/nodejs:22.2025.10.29.20

Link to code that reproduces the bug

n/a

Expected Behavior

Response is returned immediately without an extra 10 second delay.

[adrai]

you need to find out how the lambda function is executed.... I just added a function check, but probably this will not help... (v6.3.1)

You can also try to define your lambda entry point something like this:

const proxy = awsLambdaFastify(app)
export const handler = (event, context) => proxy(event, context)