SQS and Lambda on LocalStack

In my last post I had shown how to install LocalStack on your local machine. Link is here.

In this post, lets create a queue which on recieving a message will trigger a lambda. All on LocalStack.

Creating Infrastructure

There are various ways to create infrastructure setup. I am going to use boto3 library on python.

Copy the following code to create a queue.

import boto3

# Create a Boto3 client for SQS.
sqs = boto3.client('sqs', endpoint_url='http://localhost:4566',region_name='us-west-2', aws_access_key_id="dummy", aws_secret_access_key= "dummy")
# Create a queue.
queue = sqs.create_queue(QueueName='input-queue')
print(queue)

Note the region is us-west-2. If you navigate into LocalStack desktop you should see the queue created under SQS.

Creating Lambda

Lets now create a lambda which we will evenually trigger from the queue. Lets first create a lambda. Create a python file with the following content. In my case file name is app.py

def lambda_handler(event,context):    
    return {
        "statusCode": 200,
        "body": "Lambda triggered from SQS"
    }

Lambda doesnt do much. It will just return status code as success. My folder structure is as shown below.

Create_infra.py is a file where I have kept the code to create queue, lambda, and I am going to bind them together.

Create a zip folder from app.py

Lets now write the code to create the lambda.

lambda_client = boto3.client('lambda',endpoint_url='http://localhost:4566',region_name='us-west-2', aws_access_key_id="dummy", aws_secret_access_key= "dummy")

lambda_client.create_function(
            FunctionName="test_lambda",
            Runtime='python3.8',
            Role='arn:aws:iam::000000000000:role/lambda-role',
            Handler="app.lambda_handler",
            Code=dict(ZipFile=open("app.zip", 'rb').read())
        )

Note you need to specify the zip file you created and that needs to be under same folder. Once lambda gets created you will see that in the lambda section of LocalStack desktop.

Binding Queue with Lambda

Lets now bind queue with lambda so that when a message arrives in queue, lambda is triggered. Execute the following code. Note that function name (the name of the function we created), and queue arn have to be specified. You can get the arn from the SQS section navigating to the queue.

response = lambda_client.create_event_source_mapping(
    EventSourceArn='arn:aws:sqs:us-west-2:000000000000:input-queue',
    FunctionName='test_lambda'
)

Validating the Setup

Lets now send a message into the queue. Lets navigate to SQS, and select the input-queue.

Switch to Messages in the tab.

In the bottom bar you should see the “Send Message” button. Click on it. Select the Queue Url and enter Message Body. The click Send button.

Message shows up in the list. However it will be picked up by the lambda.

Now navigate to the Lambda from the main dashboard. Select test-lambda.

Switch to Logs tab. You should see Start, End and Repor.

This means lambda is triggered by the message we sent on the queue.

Closing Note

LocalStack is one of the easy way to build the AWS workflow. Complex workflows can be built easily as POC and then migrated to production systems.

LocalStack – AWS Emulator

LocalStack is a cloud service emulator that can run on your local and gives most of what AWS cloud offers for development. You can develop code in your local, test it end to end without need of connecting to AWS. Atleast this is why I went on installing LocalStack on my machine. So far I am able to test SQS and Lambda, and it is pretty promising. 🙂

Lets see how to install LocalStack first.

Pre-requisites

I am using docker to run LocalStack since it is easy to cleanup. Make sure you install docker before continuing with next steps.

Also you need python inorder to install LocalStack.

LocalStack Installation

I had python on my machine. So I went with the following command.

python -m pip install localstack

Once done install awslocal cli. You may need to do it with elevated permission.

pip install awscli-local[ver1]

Starting LocalStack

Lets now start LocalStack with the following command. Make sure docker is running.

localstack start -d

You should see the following in the command prompt.

Validation

Lets create a SQS queue and see if it works. Execute the following command.

awslocal sqs create-queue --queue-name sample-queue
{
    "QueueUrl": "http://sqs.us-east-1.localhost.localstack.cloud:4566/000000000000/sample-queue"
}

Lets now list the queues and see queue is created from the above command.

awslocal sqs list-queues

You should see the queue.

Do I Have a UI?

Yes. There is a UI to navigate across components just like in AWS console. I downloaded it from Microsoft Store since I am using Windows 11.

Configuring LocalStack Desktop

When you open the LocalStack desktop, you will see the link

Select the link. Then enter the following endpoint.

http://localhost:4566

You will be asked to login by creating account on LocalStack. After logging in you should see the dashboard.

Some of the features are Pro features which needs to be purchased. But majority are still open to use.

Lets now select SQS in the dashboard to look at our created queue. You will see the created queue as shown below.

Closing Note

Running and testing the program on local is much much faster than on the cloud. LocalStack can significantly reduce the turn around time of building quality AWS program or architecture. I see LocalStack even support writing program with AWS CDK. I have not gone too far in it. I am impressed.