Deploy Go Lambda within Docker container

Question

I have a Go Lambda function. I want to host that function in a Docker image/container so that I can test it locally. In this effort, I have followed the instructions provided here. From those instructions, I have the following files:

• .
  • Dockerfile
  • go.mod
  • go.sum
  • main.go

Those files contain the following:

Dockerfile (a copy of the Dockerfile in this section)

FROM alpine as build

# install build tools
RUN apk add go git
RUN go env -w GOPROXY=direct

# cache dependencies
ADD go.mod go.sum ./
RUN go mod download 

# build
ADD . .
RUN go build -o /main

# copy artifacts to a clean image
FROM alpine
COPY --from=build /main /main
ENTRYPOINT [ "/main" ] 

go.mod (an updated version of this go.mod)

module main

go 1.18

require (
    github.com/aws/aws-lambda-go v1.32.1
    github.com/aws/aws-sdk-go v1.44.60
)

require github.com/jmespath/go-jmespath v0.4.0 // indirect

go.sum (a modified version of this go.sum)

github.com/aws/aws-lambda-go v1.32.1 h1:ls0FU8Mt7ayJszb945zFkUfzxhkQTli8mpJstVcDtCY=
github.com/aws/aws-lambda-go v1.32.1/go.mod h1:jwFe2KmMsHmffA1X2R09hH6lFzJQxzI8qK17ewzbQMM=
github.com/aws/aws-sdk-go v1.44.60 h1:KTTogelVR+4dWiIPl7eyxoxaJkziChON6/Y/hVfTipk=
github.com/aws/aws-sdk-go v1.44.60/go.mod h1:y4AeaBuwd2Lk+GepC1E9v0qOiTws0MIWAX4oIKwKHZo=
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/jmespath/go-jmespath v0.4.0 h1:BEgLn5cpjn8UN1mAw4NjwDrS35OdebyEtFe+9YPoQUg=
github.com/jmespath/go-jmespath v0.4.0/go.mod h1:T8mJZnbsbmF+m6zOOFylbeCJqk5+pHWvzYPziyZiYoo=
github.com/jmespath/go-jmespath/internal/testify v1.5.1 h1:shLQSRRSCCPj3f2gpwzGwWFoC7ycTf1rcQZHOlsJ6N8=
github.com/jmespath/go-jmespath/internal/testify v1.5.1/go.mod h1:L3OGu8Wl2/fWfCI6z80xFu9LTZmf1ZRjMHUOPmWr69U=
github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/testify v1.7.2 h1:4jaiDzPyXQvSd7D0EjG45355tLlV3VOECpq10pLC+8s=
golang.org/x/net v0.0.0-20220127200216-cd36cc0744dd/go.mod h1:CfG3xpIq0wQ8r1q4Su4UZFWDARRcnwPjda9FqA0JpMk=
golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.0.0-20211216021012-1d35b9e2eb4e/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

main.go (a copy of this main.go)

package main

import (
    "context"
    "encoding/json"
    "log"
    "os"

    "github.com/aws/aws-lambda-go/events"
    runtime "github.com/aws/aws-lambda-go/lambda"
    "github.com/aws/aws-lambda-go/lambdacontext"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/lambda"
)

var client = lambda.New(session.New())

func callLambda() (string, error) {
    input := &lambda.GetAccountSettingsInput{}
    req, resp := client.GetAccountSettingsRequest(input)
    err := req.Send()
    output, _ := json.Marshal(resp.AccountUsage)
    return string(output), err
}

func handleRequest(ctx context.Context, event events.SQSEvent) (string, error) {
    // event
    eventJson, _ := json.MarshalIndent(event, "", "  ")
    log.Printf("EVENT: %s", eventJson)
    // environment variables
    log.Printf("REGION: %s", os.Getenv("AWS_REGION"))
    log.Println("ALL ENV VARS:")
    for _, element := range os.Environ() {
        log.Println(element)
    }
    // request context
    lc, _ := lambdacontext.FromContext(ctx)
    log.Printf("REQUEST ID: %s", lc.AwsRequestID)
    // global variable
    log.Printf("FUNCTION NAME: %s", lambdacontext.FunctionName)
    // context method
    deadline, _ := ctx.Deadline()
    log.Printf("DEADLINE: %s", deadline)
    // AWS SDK call
    usage, err := callLambda()
    if err != nil {
        return "ERROR", err
    }
    return usage, nil
}

func main() {
    runtime.Start(handleRequest)
}

I can successfully run:

go mod tidy
go build

I can also successfully build and run my Docker image using:

docker build -t lambda-fn .
docker run -d -v ~/.aws-lambda-rie:/aws-lambda --entrypoint /aws-lambda/aws-lambda-rie  -p 9000:8080 lambda-fn:latest /main

I can see a container based on the lambda-fn image listed, with a status of Running, in Docker desktop. However, when I send the following cURL request, nothing happens:

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

I was expecting some logs to be written based on the contents of the handleRequest function. What am I doing wrong?

Answer 1

If you are running in demon mode (-d) you cannot see the logs.

Remove -d and rerun the command

This is due the empty handler registration. You can set the handler name by passing the extra argument

docker run -d -v ~/.aws-lambda-rie:/aws-lambda --entrypoint /aws-lambda/aws-lambda-rie  -p 9000:8080 lambda-fn:latest /main handleRequest