Which Golang Lambda Handler do you use to access Serverless Framework Input Key Value Map?

Question

I copied multiple examples from a different question to try to pass input parameters to an AWS Lambda GoLang function with the Serverless framework. The function is defined below:

functions:
  schedule:
    handler: bin/schedule
    package:
      artifact: bin/schedule.zip
    events:
      - schedule:
          rate: rate(1 minute)
          enabled: true
          input:
            key: first
      - schedule:
          rate: rate(1 minute)
          input: '{"key": "second"}'
          enabled: true
      - schedule:
          rate: rate(1 minute)
          input:
            key: 'third'
          enabled: true

But the standard Lambda Context doesn't seem to be passing in any of the input values that I'm looking for.

So which lambda handler function should I be using to access either first , second , or third values when invoking the function?

I'm trying to run multiple CRON jobs via the schedule function and I want to be able to differentiate between nightly, monthly, and yearly jobs. And I want to use the input Serverless parameter in order to differentiate the calls.

Here's what I have so far:

func Handler(ctx context.Context) error {
    fmt.Println(fmt.Sprintf("ctx is [%+v]", ctx))
    fmt.Println(fmt.Sprintf("ctx value is [%+v]", ctx.Value("schedule")))
    lambdaContext, exists := lambdacontext.FromContext(ctx)
    if exists {
        fmt.Println(fmt.Sprintf("lambdaContext is [%+v]", lambdaContext))
        fmt.Println(fmt.Sprintf("lambdaContext.ClientContext is [%+v]", lambdaContext.ClientContext))
        fmt.Println(fmt.Sprintf("lambdaContext.ClientContext.Client is [%+v]", lambdaContext.ClientContext.Client))
        fmt.Println(fmt.Sprintf("lambdaContext.ClientContext.Custom  is [%+v]", lambdaContext.ClientContext.Custom))
        fmt.Println(fmt.Sprintf("lambdaContext.ClientContext.Env is [%+v]", lambdaContext.ClientContext.Env))

    } else {
        fmt.Println("no lambda context")
    }
    return nil
}

And here's the output that it produces:

2022-09-27T11:39:16.137-05:00   ctx is [context.Background.WithDeadline(2022-09-27 16:39:22.135397493 +0000 UTC [5.998625784s]).WithValue(type *lambdacontext.key, val <not Stringer>).WithValue(type string, val Root=1-63332733-1ebfc3d83a8de600668c194d;Parent=28a5686a7181409c;Sampled=0)]

2022-09-27T11:39:16.137-05:00   ctx value is [<nil>]

2022-09-27T11:39:16.137-05:00   lambdaContext is [&{AwsRequestID:914686cf-e4eb-4e04-a0d8-58f5ea60247b InvokedFunctionArn:arn:aws:lambda:us-east-2:631520639713:function:laguna-seca-staging-schedule Identity:{CognitoIdentityID: CognitoIdentityPoolID:} ClientContext:{Client:{InstallationID: AppTitle: AppVersionCode: AppPackageName:} Env:map[] Custom:map[]}}]

2022-09-27T11:39:16.137-05:00   lambdaContext.ClientContext is [{Client:{InstallationID: AppTitle: AppVersionCode: AppPackageName:} Env:map[] Custom:map[]}]

2022-09-27T11:39:16.137-05:00   lambdaContext.ClientContext.Client is [{InstallationID: AppTitle: AppVersionCode: AppPackageName:}]

2022-09-27T11:39:16.137-05:00   lambdaContext.ClientContext.Custom is [map[]]

2022-09-27T11:39:16.137-05:00   lambdaContext.ClientContext.Env is [map[]]

As you can see there's no mention of first , second , or third . I was hoping to be able to see the value(s) in either the .Custom or .Env maps but those are both empty.

Answer 1

Okay after hours I finally figured this out. If you're curious for more information about this here was my thought process.

1. The google search
2. The corresponding result that helped: Serverless Event Constant Inputs
3. The AWS Article that it references for sending static JSON to your Lambda events

Once I saw that it was trigged by CloudWatch to have manual JSON that got me thinking that I need to have a value of json or string or map in one of the AWS Lambda GoLang Event handlers . The problem is that none of the cloudwatch events correctly unmarshalled the value that I needed. Which made me think: why not try my own value for the handler function? That is one of the approved Handler invocations in the AWS Lambda GoLang Handler documentation . So I created my own object and it worked perfectly. Here's the final implementation for a nightly and monthly CRON scheduled Serverless Framework AWS Lambda GoLang function:

serverless.yaml:

functions:
  ...
  schedule:
    handler: bin/schedule
    package:
      artifact: bin/schedule.zip
    events:
      - schedule:
          rate: rate(1 day)
          input:
            key: 'nightly'
          enabled: true
      - schedule:
          rate: rate(30 days)
          input:
            key: 'monthly'
          enabled: true
   ...

main.go:

package main

import (
    ...
)

func init() {
    // connect to your database here
}

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

type MyObject struct {
    Key string `json:"key"`
}

func Handler(_ context.Context, myObject MyObject) error {
    fmt.Println(fmt.Sprintf("event is [%+v]", myObject))
    return nil
}

And on invocation this prints: nightly by the minutely schedule and monthly by the hourly schedule.