golang lambda docker from alternative image

I'm trying to create a docker image for lambda running a golang handler, but which does not take from public.ecr.aws/lambda/go:1 or public.ecr.aws/lambda/provided:al2.

I tried to follow the steps on aws documentation for alternative base image.

And also this tutorial:
https://hichaelmart.medium.com/using-container-images-with-aws-lambda-7ffbd23697f1

It just won't work. The lambda starts but won't serve any requests. Making a request:

curl -XPOST "http://localhost:9000/2015-03-31/functions/function/invocations" -d '{"body":{"name":"Test"}}'

Never returns.

If I use public.ecr.aws/lambda/go:1 it works fine.

From what I've seen, it might be missing the "runtime interface" but their go api claims to be implementing it as a wrapper to the handler code.

This is my Dockerfile

FROM alpine:3.16

ADD https://github.com/aws/aws-lambda-runtime-interface-emulator/releases/latest/download/aws-lambda-rie /usr/bin/aws-lambda-rie
RUN chmod 755 /usr/bin/aws-lambda-rie

WORKDIR /var/task

COPY main ./

ENTRYPOINT ["/usr/bin/aws-lambda-rie", "/var/task/main"]

This is my lambda handler

type MyEvent struct {
	Name string `json:"name"`
}

func HandleRequest(_ context.Context, name MyEvent) (string, error) {
	return fmt.Sprintf("Hello %s!", name.Name), nil
}

func main() {
	lambda.Start(HandleRequest)
}

The logs on the docker serving the requests are

15 May 2023 06:34:03,985 [INFO] (rapid) exec '/var/task/main' (cwd=/var/task, handler=/var/task/main)
15 May 2023 06:34:08,178 [INFO] (rapid) extensionsDisabledByLayer(/opt/disable-extensions-jwigqn8j) -> stat /opt/disable-extensions-jwigqn8j: no such file or directory
15 May 2023 06:34:08,180 [INFO] (rapid) Configuring and starting Operator Domain
15 May 2023 06:34:08,182 [INFO] (rapid) Starting runtime domain
15 May 2023 06:34:08,188 [WARNING] (rapid) Cannot list external agents error=open /opt/extensions: no such file or directory
START RequestId: dfbc9842-2a7b-4a3e-bfd2-2434aa126f63 Version: $LATEST
15 May 2023 06:34:08,198 [INFO] (rapid) Starting runtime without AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY, AWS_SESSION_TOKEN , Expected?: false
START RequestId: 5e0f07ac-46a3-42e0-8a60-851293544020 Version: $LATEST

Any help on what I need to add to the Dockerfile would be appreciated.

It's not clear how the main binary is built, but it's most likely that it's not built for alpine. If you check the log of the container, you should see something like this:

[WARNING] (rapid) First fatal error stored in appctx: Runtime.InvalidEntrypoint
[ERROR] (rapid) Init failed error=fork/exec /var/task/main: no such file or directory InvokeID=

The solutions are:

• either replace the base docker image to match what main is built for;
• or rebuild the main binary for alpine.

The Dockerfile below shows how to build the main binary for alpine:

# ==== build stage ====
FROM golang:1.18.4-alpine3.16 as build

WORKDIR /app

COPY . .

RUN go build -o main .

# ==== final stage ====
FROM alpine:3.16.1

ADD https://github.com/aws/aws-lambda-runtime-interface-emulator/releases/latest/download/aws-lambda-rie /usr/bin/aws-lambda-rie
RUN chmod 755 /usr/bin/aws-lambda-rie

WORKDIR /var/task

COPY --from=build /app/main ./

ENTRYPOINT ["/usr/bin/aws-lambda-rie", "/var/task/main"]

I'm also curious about why aws-lambda-rie works on alpine. And I found that it's built with CGO_ENABLED=0 (see here). We can do the same thing because the simple demo don't need cgo:

CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -o main .

This main binary works on alpine too.