AWS Lambda Functions

AWS Lambda Functions

  • Each function has associated configuration information, such as its name, description, runtime, entry point, and resource requirements
  • Lambda functions should be designed as stateless
    • to allow launching of as many copies of the function as needed as per the demand.
    • Local file system access, child processes, and similar artifacts may not extend beyond the lifetime of the request
    • The state can be maintained externally in DynamoDB or S3
  • Lambda Execution role can be assigned to the function to grant permission to access other resources.
  • Functions have the following restrictions
    • Inbound network connections are blocked
    • Outbound connections only TCP/IP sockets are supported
    • ptrace (debugging) system calls are blocked
    • TCP port 25 traffic is also blocked as an anti-spam measure.
  • Lambda may choose to retain an instance of the function and reuse it to serve a subsequent request, rather than creating a new copy.
  • Lambda Layers provide a convenient way to package libraries and other dependencies that you can use with your Lambda functions.
  • Function versions can be used to manage the deployment of the functions.
  • Function Alias supports creating aliases, which are mutable, for each function version.
  • Functions have the following limits
    • RAM – 128 MB to 10,240 MB (10 GB)
    • CPU is linked to RAM and cannot be set manually.
      • 2 vCPUs = 1769 MB RAM
      • 6 vCPUs = 10240 MB RAM
    • Timeout – 900 Secs or 15 mins
    • /tmp storage between 512 MB and 10,240 MB
    • Deployment Package – 50 MB (zipped), 250 MB (unzipped) including layers
    • Concurrent Executions – 1000 (soft limit)
    • Container Image Size – 10 GB
    • Invocation Payload (request/response) – 6 MB (sync), 256 KB (async)
  • Functions are automatically monitored, and real-time metrics are reported through CloudWatch, including total requests, latency, error rates, and throttled requests.
  • Lambda automatically integrates with CloudWatch logs, creating a log group for each function and providing basic application lifecycle event log entries, including logging the resources consumed for each use of that function.
  • Functions support code written in
    • Node.js (JavaScript)
    • Python
    • Ruby
    • Java (Java 8 compatible)
    • C# (.NET Core)
    • Go
    • Custom runtime
  • Container images are also supported.
  • Failure Handling
    • For S3 bucket notifications and custom events, Lambda will attempt execution of the function three times in the event of an error condition in the code or if a service or resource limit is exceeded.
    • For ordered event sources that Lambda polls, e.g. DynamoDB Streams and Kinesis streams, it will continue attempting execution in the event of a developer code error until the data expires.
    • Kinesis and DynamoDB Streams retain data for a minimum of 24 hours
    • Dead Letter Queues (SNS or SQS) can be configured for events to be placed, once the retry policy for asynchronous invocations is exceeded

Lambda Layers

  • Lambda Layers provide a convenient way to package libraries and other dependencies that you can use with your Lambda functions.
  • Layers help reduce the size of uploaded deployment archives and make it faster to deploy your code.
  • A layer is a .zip file archive that can contain additional code or data.
  • A layer can contain libraries, a custom runtime, data, or configuration files.
  • Layers promote reusability, code sharing, and separation of responsibilities so that you can iterate faster on writing business logic.
  • Layers can be used only with Lambda functions deployed as a .zip file archive.
  • For functions defined as a container image, the preferred runtime and all code dependencies can be packaged when the container image is created.
  • A Layer can be created by bundling the content into a .zip file archive and uploading the .zip file archive to the layer from S3 or the local machine.
  • Lambda extracts the layer contents into the /opt directory when setting up the execution environment for the function.

Environment Variables

  • Environment variables can be used to adjust the function’s behavior without updating the code.
  • An environment variable is a pair of strings that are stored in a function’s version-specific configuration.
  • The Lambda runtime makes environment variables available to the code and sets additional environment variables that contain information about the function and invocation request.
  • Environment variables are not evaluated prior to the function invocation.
  • Lambda stores environment variables securely by encrypting them at rest.
  • AWS recommends using Secrets Manager instead of storing secrets in the environment variables.

Lambda Function Limits

  • RAM – 128 MB to 10,240 MB (10 GB)
  • CPU is linked to RAM and cannot be set manually.
    • 2 vCPUs = 1769 MB RAM
    • 6 vCPUs = 10240 MB RAM
  • Timeout – 900 Secs or 15 mins
  • /tmp storage between 512 MB and 10,240 MB
  • Deployment Package – 50 MB (zipped), 250 MB (unzipped) including layers
  • Concurrent Executions – 1000 (soft limit)
  • Container Image Size – 10 GB
  • Invocation Payload (request/response) – 6 MB (sync), 256 KB (async)

Lambda Functions Versioning

  • Function versions can be used to manage the deployment of the functions.
  • Each function has a single, current version of the code.
  • Lambda creates a new version of the function each time it’s published.
  • A function version includes the following information:
    • The function code and all associated dependencies.
    • The Lambda runtime that invokes the function.
    • All the function settings, including the environment variables.
    • A unique Amazon Resource Name (ARN) to identify the specific version of the function.
  • Function versions are immutable, however, support Aliases which are mutable.

Lambda Functions Alias

  • Lambda supports creating aliases, which are mutable, for each function version.
  • Alias is a pointer to a specific function version, with a unique ARN.
  • Each alias maintains an ARN for a function version to which it points.
  • An alias can only point to a function version, not to another alias
  • Alias helps in rolling out new changes or rolling back to old versions
  • Alias supports routing configuration to point to a maximum of two Lambda function versions. It can be used for canary testing to send a portion of traffic to a second function version.

References

AWS_Lambda_Functions

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