What is Function as a Service (FaaS)?

Function as a Service (FaaS) is a cloud computing model that lets developers deploy individual functions or pieces of code without managing the underlying infrastructure. These functions are triggered by specific events, such as HTTP requests, database changes, or file uploads, and the cloud provider automatically handles scaling, server provisioning, and resource allocation. Examples include AWS Lambda, Azure Functions, and Google Cloud Functions. With FaaS, developers focus solely on writing code for discrete tasks, while the platform manages execution, runtime environments, and availability.

FaaS works by breaking applications into small, stateless functions that run in ephemeral containers. When an event occurs—like an API request or a message in a queue—the cloud provider spins up a container to execute the function, then shuts it down once the task is complete. For instance, a function could resize an image when a file is uploaded to a storage bucket. The key advantage is automatic scaling: if thousands of requests arrive simultaneously, the platform launches multiple instances of the function to handle the load. This eliminates the need to pre-allocate servers or worry about capacity. Costs are typically based on execution time and memory usage, making it economical for sporadic workloads.

FaaS is best suited for event-driven, short-lived tasks. Common use cases include processing data streams, handling webhooks, or building microservices. For example, a backend for a mobile app might use FaaS to validate user input, update a database, or send notifications. However, FaaS has limitations. Functions are stateless, so persistent data must be stored externally, and cold starts (delays when a function hasn’t been used recently) can affect performance. Developers must also design functions to run quickly, as most platforms impose time limits (e.g., 15 minutes). Despite these constraints, FaaS simplifies deployment and reduces operational overhead, letting teams iterate faster on specific features without managing servers.