Building and deploying multiple Go lambdas via images in AWS with differing Go packages from one Dockerfile

I'm trying to build and deploy multiple Go based lambdas using 1 Dockerfile (as the instructions don't differ between lambdas) using different go packages for each lambda.

My file structure is as follows:

test-lambda
|------ go.mod
|------ go.sum
|------ main.go
test-lambda-2
|------ go.mod
|------ go.sum
|------ main.go
Dockerfile
...other repo files

My Dockerfile looks like the following:

FROM golang:1.24.3 AS builder

ARG LAMBDA_DIR

RUN echo $LAMBDA_DIR

WORKDIR ${LAMBDA_DIR}
COPY * /lambda/
RUN CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -C /lambda -a -installsuffix cgo -o lambda
RUN chmod +x /lambda/lambda

FROM public.ecr.aws/lambda/provided:al2023-arm64

COPY --from=builder lambda/lambda /usr/local/bin/lambda

ENTRYPOINT [ "lambda" ]

I am using AWS CloudFormation and SAM to build and deploy the lambdas. My template.yaml looks like this

AWSTemplateFormatVersion: 2010-09-09
Transform: AWS::Serverless-2016-10-31

Globals:
  Function:
    Architectures: [arm64]
    Timeout: 900
    MemorySize: 1024

Parameters:
  CommitHash:
    Type: String
    Description: Commit hash of the change

Resources:
  TestLambda:
    Type: AWS::Serverless::Function
    Properties:
      PackageType: Image
    Metadata:
      Dockerfile: Dockerfile
      DockerContext: .
      DockerTag: !Ref CommitHash
      DockerBuildArgs:
        LAMBDA_DIR: /test-lambda

  TestLambda2:
    Type: AWS::Serverless::Function
    Properties:
      PackageType: Image
    Metadata:
      Dockerfile: Dockerfile
      DockerContext: .
      DockerTag: !Ref CommitHash
      DockerBuildArgs:
        LAMBDA_DIR: /test-lambda-2

I am then using a justfile to make running the commands easier in CI (GitLab). The commands are as follows:

build:
    sam build \
    --use-container \
    -t template.yaml \
    --parameter-overrides CommitHash=$CI_COMMIT_SHORT_SHA \
    --debug

deploy:
    sam deploy \
    --stack-name $CI_PROJECT_NAME--$CI_COMMIT_BRANCH \
    --region eu-west-2 \
    --profile $CI_PROJECT_NAME \
    --resolve-s3 \
    --resolve-image-repos \
    --capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM \
    --parameter-overrides CommitHash=$CI_COMMIT_SHORT_SHA \
    --tags Service=$CI_PROJECT_NAME Repo=$CI_PROJECT_URL Version=$CI_COMMIT_SHORT_SHA

My main.go's look like this:

// main.go
package main

import (
    "github.com/aws/aws-lambda-go/lambda"
)

func hello() (string, error) {
    return "Hello λ!", nil
}

func main() {
    // Make the handler available for Remote Procedure Call by AWS Lambda
    lambda.Start(hello)
}

The only difference between the 2 is the returned string differs between each lambda package so that I can test they're different. The test-lambda-2 returns return "Hello λ2!", nil for example.

This builds fine, but the issue I am having is that both lambdas are seemingly using the same image, and returning the output of the test-lambda-2 package, and not the respective packages.

I can provide the CI output if necessary, but from the logs I can see 2 different images being built and 2 repos with 2 separate images in. Both lambdas point to the each repo. So it seems to be an issue with the build and not the pushing of the image.

Am I missing something obvious?

Tried adjusting the building to use container or not, and adjusted the build arg. Both result in the same thing

There are few issues with the setup, You have to fix those before trying again,

1. In your Dockerfile, the COPY instruction is incorrect. You're trying to copy files to

   /lambda/
   

   but your WORKDIR is set to

   ${LAMBDA_DIR}
   

   Also, you need to copy the specific lambda directory contents.
   Here's the corrected Dockerfile:

FROM golang:1.24.3 AS builder

ARG LAMBDA_DIR

WORKDIR /lambda
COPY ${LAMBDA_DIR} .
RUN CGO_ENABLED=0 GOOS=linux GOARCH=arm64 go build -a -installsuffix cgo -o lambda
RUN chmod +x lambda

FROM public.ecr.aws/lambda/provided:al2023-arm64

COPY --from=builder /lambda/lambda /usr/local/bin/lambda

ENTRYPOINT [ "lambda" ]

1. In your Dockerfile, the COPY instruction is incorrect.

2. In your SAM template, you should specify the function handler and other required properties[1]

3. Make sure each lambda directory has the required AWS Lambda dependencies in its go.mod: [2]

   require github.com/aws/aws-lambda-go v1.41.0
   
   

4. Each main.go should implement the Lambda handler interface

   package main
   
   import (
       "context"
       "github.com/aws/aws-lambda-go/lambda"
   )
   
   func handleRequest(ctx context.Context, event interface{}) (string, error) {
       // Your lambda logic here
       return "Hello from Lambda!", nil
   }
   
   func main() {
       lambda.Start(handleRequest)
   }
   
   

   
   go
   To build and deploy using SAM:
   
   # Build
   sam build
   
   # Deploy
   sam deploy --stack-name your-stack-name --parameter-overrides CommitHash=your-commit-hash
   
   
   

   Sources

   [1] SAM to deploy Image-Based Lambda

   [2] Deploy Lambda functions with container images - AWS Prescriptive Guidance