How AWS Lambda Works?
How AWS Lambda works is a fundamental question for developers leveraging serverless computing. AWS Lambda is a fully managed, event-driven service that runs code without provisioning or managing servers. By automatically scaling workloads, it enables businesses to focus on innovation rather than infrastructure management. But what happens behind the scenes when a function executes?
In this blog, we’ll explore the internal workings of AWS Lambda, including the Firecracker MicroVM technology, execution models, and how functions are initiated and invoked.
Firecracker MicroVM: The Core of AWS Lambda
How AWS Lambda works is deeply tied to its underlying virtualization technology—Firecracker MicroVM. Firecracker, developed by Amazon and written in Rust, powers AWS Lambda by enabling lightweight, secure, and fast microVMs (Micro Virtual Machines).
As shown in the diagram, AWS Lambda functions execute within Firecracker MicroVMs, ensuring isolation and security. Each function runs inside a sandbox with:
- A minimal Linux userland
- Essential libraries and utilities
- A dedicated execution environment (worker) on EC2 instances
This architecture ensures that multiple customers’ functions remain secure and efficiently managed while benefiting from the flexibility of serverless computing.
How AWS Lambda Works: Execution Models
There are two primary ways how AWS Lambda works in executing functions: synchronous execution and asynchronous execution.
Synchronous Execution
- Placement and Provisioning – The Worker Manager communicates with the Placement Service, which selects an appropriate host and provisions a sandbox for execution.
- Function Initialization – The Worker Manager initializes the function by downloading the Lambda package from Amazon S3 and setting up the Lambda runtime.
- Invocation – The Frontend Worker invokes the function, allowing it to execute within the prepared environment.
Asynchronous Execution
- Queue-Based Processing – The Application Load Balancer forwards the request to a Frontend Worker, which places the event into an internal queue (such as Amazon SQS).
- Polling and Execution – Pollers monitor the queue and transfer events to the Frontend Worker, following the synchronous execution model to complete the function execution.
Conclusion
Understanding how AWS Lambda works is essential for developers building scalable and efficient serverless applications. With Firecracker MicroVMs, AWS Lambda ensures high performance, security, and rapid execution. Whether using synchronous or asynchronous execution models, Lambda optimizes workload management, making serverless computing more powerful than ever.
For a deeper dive into AWS Lambda’s evolution and best practices, check out:
AWS Lambda: 10 Years of Innovation Unpacking AWS Lambda: A Comprehensive Guide
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