AWS Lambda vs Amazon SQS: What are the differences?

Introduction

In this markdown, we will discuss the key differences between AWS Lambda and Amazon SQS. Both AWS Lambda and Amazon Simple Queue Service (SQS) are services provided by Amazon Web Services (AWS) that enable developers to build scalable and efficient applications. However, they have distinct functionalities and use cases.

1. Scalability: AWS Lambda is a serverless computing service that automatically scales to handle a high volume of requests. It allows developers to run code without provisioning or managing servers. On the other hand, Amazon SQS is a fully managed message queuing service that provides distributed message queues for storing messages as they travel between different components of a distributed application. It enables decoupling of the sender and receiver, allowing scalability within the application itself.

2. Invocation: AWS Lambda functions are triggered by events such as changes to data in an Amazon S3 bucket, updates to an Amazon DynamoDB table, or an HTTP request through Amazon API Gateway. These events invoke the Lambda function, which executes the code. On the contrary, Amazon SQS allows messages to be sent and received by any component of a distributed application. It decouples the sender from the receiver and allows the receiver to process messages at its own pace.

3. Compute Resource: AWS Lambda functions are executed on demand, meaning that the necessary compute resources are automatically provisioned by AWS to execute the code. The function's execution environment is managed by AWS. In contrast, Amazon SQS does not execute any code itself. It simply acts as a message queue, storing messages until they are processed by a separate component or worker.

4. Message Persistence: In AWS Lambda, messages are not persisted by default. The function is invoked with an event, processes it, and generates a response. There is no storage of messages for future retrieval. On the other hand, Amazon SQS guarantees message persistence. Messages sent to an SQS queue are stored redundantly across multiple availability zones to provide durability. The messages can be stored in the queue for a configurable retention period.

5. Concurrency: AWS Lambda functions can scale horizontally to handle multiple requests concurrently. Each instance of the Lambda function can process a single event at a time in a separate container. The number of concurrent executions can be configured to meet the application's requirements. On the other hand, Amazon SQS can handle multiple concurrent workers that retrieve and process messages from the queue. The number of workers can be adjusted to achieve the desired throughput.

6. Billing: AWS Lambda pricing is based on the number of requests and the duration of both the execution and the memory allocated. Users pay only for the compute resources actually consumed during code execution. Amazon SQS pricing is based on the number of requests made to the service, as well as the volume of data transferred and stored in the queues. Users pay for the number of messages sent, received, or deleted, and for storage consumed by messages.

In summary, AWS Lambda is a serverless compute service that automatically scales to handle requests, while Amazon SQS is a managed message queuing service that provides distributed message queues. Lambda executes code on demand, while SQS acts as a persistent storage and decoupling mechanism. Lambda scales horizontally with concurrent executions, while SQS handles multiple worker processes. The pricing models also differ between the two services.