Lambda features - AWS Lambda

Lambda features

Lambda provides a management console and API for managing and invoking functions. It provides runtimes that support a standard set of features so that you can easily switch between languages and frameworks, depending on your needs. In addition to functions, you can also create versions, aliases, layers, and custom runtimes.

Programming model

Authoring specifics vary between runtimes, but all runtimes share a common programming model that defines the interface between your code and the runtime code. You tell the runtime which method to run by defining a handler in the function configuration, and the runtime runs that method. The runtime passes in objects to the handler that contain the invocation event and the context, such as the function name and request ID.

When the handler finishes processing the first event, the runtime sends it another. The function's class stays in memory, so clients and variables that are declared outside of the handler method in initialization code can be reused. To save processing time on subsequent events, create reusable resources like AWS SDK clients during initialization. Once initialized, each instance of your function can process thousands of requests.

Initialization is billed as part of the duration for the first invocation that an instance of your function processes. When AWS X-Ray tracing is enabled, the runtime records separate subsegments for initialization and execution.

        An X-Ray trace with initialization and invocation subsegments.

Your function also has access to local storage in the /tmp directory. Instances of your function that are serving requests remain active for a few hours before being recycled.

The runtime captures logging output from your function and sends it to Amazon CloudWatch Logs. In addition to logging your function's output, the runtime also logs entries when function invocation starts and ends. This includes a report log with the request ID, billed duration, initialization duration, and other details. If your function throws an error, the runtime returns that error to the invoker.


Logging is subject to CloudWatch Logs quotas. Log data can be lost due to throttling or, in some cases, when an instance of your function is stopped.

For a hands-on introduction to the programming model in your preferred programming language, see the following chapters.

Lambda scales your function by running additional instances of it as demand increases, and by stopping instances as demand decreases. Unless noted otherwise, incoming requests might be processed out of order or concurrently. Store your application's state in other services, and don't rely on instances of your function being long lived. Use local storage and class-level objects to increase performance, but keep to a minimum the size of your deployment package and the amount of data that you transfer onto the execution environment.


Lambda manages the infrastructure that runs your code, and scales automatically in response to incoming requests. When your function is invoked more quickly than a single instance of your function can process events, Lambda scales up by running additional instances. When traffic subsides, inactive instances are frozen or stopped. You only pay for the time that your function is initializing or processing events.

        Your function scales automatically based on the number of open requests.

For more information, see AWS Lambda function scaling.

Concurrency controls

Use concurrency settings to ensure that your production applications are highly available and highly responsive. To prevent a function from using too much concurrency, and to reserve a portion of your account's available concurrency for a function, use reserved concurrency. Reserved concurrency splits the pool of available concurrency into subsets. A function with reserved concurrency only uses concurrency from its dedicated pool.

        Reserved concurrency allocated to two functions.

To enable functions to scale without fluctuations in latency, use provisioned concurrency. For functions that take a long time to initialize, or that require extremely low latency for all invocations, provisioned concurrency enables you to pre-initialize instances of your function and keep them running at all times. Lambda integrates with Application Auto Scaling to support autoscaling for provisioned concurrency based on utilization.

        Autoscaling provisioned concurrency with Application Auto Scaling.

For more information, see Managing concurrency for a Lambda function.

Asynchronous invocation

When you invoke a function, you can choose to invoke it synchronously or asynchronously. With synchronous invocation, you wait for the function to process the event and return a response. With asynchronous invocation, Lambda queues the event for processing and returns a response immediately.

        Lambda queues asynchronous invocation events before sending them to the function.

For asynchronous invocations, Lambda handles retries if the function returns an error or is throttled. To customize this behavior, you can configure error handling settings on a function, version, or alias. You can also configure Lambda to send events that failed processing to a dead-letter queue, or to send a record of any invocation to a destination.

For more information, see Asynchronous invocation.

Event source mappings

To process items from a stream or queue, you can create an event source mapping. An event source mapping is a resource in Lambda that reads items from an Amazon Simple Queue Service (Amazon SQS) queue, an Amazon Kinesis stream, or an Amazon DynamoDB stream, and sends the items to your function in batches. Each event that your function processes can contain hundreds or thousands of items.

        An event source mapping reading records from a Kinesis stream.

Event source mappings maintain a local queue of unprocessed items and handle retries if the function returns an error or is throttled. You can configure an event source mapping to customize batching behavior and error handling, or to send a record of items that fail processing to a destination.

For more information, see AWS Lambda event source mappings.


A destination is an AWS resource that receives invocation records for a function. For asynchronous invocation, you can configure Lambda to send invocation records to a queue, topic, function, or event bus. You can configure separate destinations for successful invocations and events that failed processing. The invocation record contains details about the event, the function's response, and the reason that the record was sent.

        Lambda sends invocation records to a queue or event bus destination, depending on the result.

For event source mappings that read from streams, you can configure Lambda to send a record of batches that failed processing to a queue or topic. A failure record for an event source mapping contains metadata about the batch, and it points to the items in the stream.

For more information, see Configuring destinations for asynchronous invocation and the error handling sections of Using AWS Lambda with Amazon DynamoDB and Using AWS Lambda with Amazon Kinesis.

Function blueprints

When you create a function in the Lambda console, you can choose to start from scratch, use a blueprint, use a container image, or deploy an application from the AWS Serverless Application Repository. A blueprint provides sample code that shows how to use Lambda with an AWS service or a popular third-party application. Blueprints include sample code and function configuration presets for Node.js and Python runtimes.

Blueprints are provided for use under the Creative Commons Zero license. They are available only in the Lambda console.

Testing and deployment tools

Lambda supports deploying code as is or as container images. You can use a rich tools ecosystem for authoring, building, and deploying your Lambda functions using AWS and popular community tools like the Docker command line interface (CLI).

For more information, see Tools for working with Lambda.

Application templates

You can use the Lambda console to create an application with a continuous delivery pipeline. Application templates in the Lambda console include code for one or more functions, an application template that defines functions and supporting AWS resources, and an infrastructure template that defines an AWS CodePipeline pipeline. The pipeline has build and deploy stages that run every time you push changes to the included Git repository.

Application templates are provided for use under the MIT No Attribution license. They are available only in the Lambda console.

For more information, see Creating an application with continuous delivery in the Lambda console.