Retrieve the SQS Queue URL dynamically from the lambda event or context

Question

I have a single lambda function which responds to two different SQS queues invoking it (the second one is a back-off queue) and so I want to dynamically determine which queue the message came from, so that I can remove it once it has been processed.

I am able to create the EventSourceMapping to trigger the lambda from both queues, but I cannot see how I cleanly retrieve the QueueURL I need in order to perform a DeleteMessage call. I am using the AWS Golang SDK.

There is the EventSourceArn in the body of the event messages and it seems I could use GetQueueURL but that would be an additional API call.

The only way to avoid that (I can think of) is to pass both queue URLs in as environment variables and use the queue name from EventSourceArn to find it.

Is there a better way that this? Is there something hiding in the context that isn't documented?

George Richardson · Accepted Answer · 2022-12-11 16:19:59Z

You can rebuild the queue URL from its ARN which you have in the event as EventSourceARN.

package main

import (
    "context"
    "fmt"

    "github.com/aws/aws-lambda-go/events"
    "github.com/aws/aws-lambda-go/lambda"
    "github.com/aws/aws-sdk-go/aws/arn"
    "github.com/aws/aws-sdk-go/aws/session"
    "github.com/aws/aws-sdk-go/service/sqs"
)

var client *sqs.SQS

func main() {
  client = sqs.New(session.Must(session.NewSessionWithOptions(session.Options{
        SharedConfigState: session.SharedConfigEnable,
    })))
    lambda.Start(Handle)
}

func Handle(ctx context.Context, event events.SQSEvent) {  
    for _, record := range event.Records {
        // Process message
        fmt.Printf(record.Body)

        // Rebuild Queue URL from ARN 
        queueArn, _ := arn.Parse(record.EventSourceARN)
        queueUrl := fmt.Sprintf("https://sqs.%v.amazonaws.com/%v/%v", queueArn.Region, queueArn.AccountID, queueArn.Resource)

        // Delete message from queue
        client.DeleteMessage(&sqs.DeleteMessageInput{
            QueueUrl:      &queueUrl,
            ReceiptHandle: &record.ReceiptHandle,
        })
    }
}

If you are using a non-standard AWS partition (e.g. China) you will also need to change the root domain of the URL to match.

aherve · Accepted Answer · 2021-08-12 19:50:23Z

1

If you are using lambda, SQS and an event-source-mapping, then you don't have to manually delete objects from sqs: When your function successfully processes a batch, Lambda deletes its messages from the queue

Just return a success code, and the message will automatically be deleted from the relevant SQS queue

answered Aug 12, 2021 at 19:50

aherve

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1 Comment

Bob Hinchliffe Over a year ago

Thanks. I guess I was trying to make sure I could delete particular messages from the batch but I don't necessarily need to.

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