Lambda concepts - AWS Lambda

Lambda concepts

With Lambda, you run functions to process events. To send events to your function, you can invoke it using the Lambda API, or you can configure an AWS service or resource to invoke it.


A function is a resource that you can invoke to run your code in Lambda. A function has code to process the events that you pass into the function or that other AWS services send to the function.

For more information, see Managing AWS Lambda functions.


When you invoke or view a function, you can include a qualifier to specify a version or alias. A version is an immutable snapshot of a function's code and configuration that has a numerical qualifier. For example, my-function:1. An alias is a pointer to a version that you can update to map to a different version, or split traffic between two versions. For example, my-function:BLUE. You can use versions and aliases together to provide a stable interface for clients to invoke your function.

For more information, see Lambda function versions.

Execution environment

An execution environment provides a secure and isolated runtime environment for your Lambda function. An execution environment manages the processes and resources that are required to run the function. The execution environment provides lifecycle support for the function and for any extensions associated with your function.

For more information, see AWS Lambda execution environment.

Deployment package

You deploy your Lambda function code using a deployment package. Lambda supports two types of deployment packages:

  • A .zip file archive that contains your function code and its dependencies. Lambda provides the operating system and runtime for your function.

  • A container image that is compatible with the Open Container Initiative (OCI) specification. You add your function code and dependencies to the image. You must also include the operating system and a Lambda runtime.

For more information, see Lambda deployment packages.


A Lambda layer is a .zip file archive that contains libraries, a custom runtime, or other dependencies. You can use a layer to distribute a dependency to multiple functions. You do not use layers with container images. Instead, you package your preferred runtime, libraries, and other dependencies into the container image when you build the image.

For more information, see Lambda layers.


The runtime provides a language-specific environment that runs in an execution environment. The runtime relays invocation events, context information, and responses between Lambda and the function. You can use runtimes that Lambda provides, or build your own. If you package your code as a .zip file archive, you must configure your function to use a runtime that matches your programming language. For a container image, you include the runtime when you build the image.

For more information, see Lambda runtimes.


Lambda extensions enable you to augment your functions. For example, you can use extensions to integrate your functions with your preferred monitoring, observability, security, and governance tools. You can choose from a broad set of tools that AWS Lambda Partners provides, or you can create your own Lambda extensions.

An internal extension runs in the runtime process and shares the same lifecycle as the runtime. An external extension runs as a separate process in the execution environment. The external extension is initialized before the function is invoked, runs in parallel with the function's runtime, and continues to run after the function invocation is complete.

For more information, see Using Lambda extensions.


An event is a JSON-formatted document that contains data for a Lambda function to process. The runtime converts the event to an object and passes it to your function code. When you invoke a function, you determine the structure and contents of the event.

Example custom event – weather data

{ "TemperatureK": 281, "WindKmh": -3, "HumidityPct": 0.55, "PressureHPa": 1020 }

When an AWS service invokes your function, the service defines the shape of the event.

Example service event – Amazon SNS notification

{ "Records": [ { "Sns": { "Timestamp": "2019-01-02T12:45:07.000Z", "Signature": "tcc6faL2yUC6dgZdmrwh1Y4cGa/ebXEkAi6RibDsvpi+tE/1+82j...65r==", "MessageId": "95df01b4-ee98-5cb9-9903-4c221d41eb5e", "Message": "Hello from SNS!", ...

For more information about events from AWS services, see Using AWS Lambda with other services.


Concurrency is the number of requests that your function is serving at any given time. When your function is invoked, Lambda provisions an instance of it to process the event. When the function code finishes running, it can handle another request. If the function is invoked again while a request is still being processed, another instance is provisioned, increasing the function's concurrency.

Concurrency is subject to quotas at the AWS Region level. You can configure individual functions to limit their concurrency, or to enable them to reach a specific level of concurrency. For more information, see Managing concurrency for a Lambda function.


A trigger is a resource or configuration that invokes a Lambda function. This includes AWS services that you can configure to invoke a function, applications that you develop, and event source mappings. An event source mapping is a resource in Lambda that reads items from a stream or queue and invokes a function. For more information, see Invoking AWS Lambda functions and Using AWS Lambda with other services.