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Cloud Computing - AWS Lambda

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Lesson Description


Lession - #1462 AWS Lambda Function Executing and Invoking


Lambda invokes your function in an execution environment, which provides a secure and isolated runtime environment. The execution environment manages the resources required to run your function. The execution environment also provides lifecycle support for the function's runtime and any external extensions associated with your function.

The function's runtime communicates with Lambda using the Runtime API. Extensions communicate with Lambda using the Extensions API. Extensions can also receive log messages from the function by subscribing to logs using the Logs API.

Architecture illustration of the execution environment.

When you create your Lambda function, you specify configuration information, similar as the amount of memory available and the maximum execution time allowed for your function. Lambda uses this information to set up the execution environment.

The function's runtime and each external extension are processes that run within the execution environment. Permissions, coffers, credentials, and environment variables are shared between the function and the extensions.

Lambda execution environment lifecycle

The lifecycle of the execution environment includes the following phases

Init In this phase, Lambda creates or unfreezes an execution environment with the configured resources, downloads the code for the function and all layers, initializes any extensions, initializes the runtime, and also runs the function’s initialization code( the code outside the main handler>
. The Init phase happens either during the first invocation, or in advance of function invocations if you have enabled provisioned concurrency.

The Init phase is split into threesub-phases Extension init, Runtime init, and Function init. Thesesub-phases ensure that all extensions and the runtime complete their setup tasks before the function code runs.

Invoke In this phase, Lambda invokes the function handler. After the function runs to completion, Lambda prepares to handle another function invocation.

Shutdown This phase is triggered if the Lambda function doesn't receive any invocations for a period of time. In the Shutdown phase, Lambda shuts down the runtime, alerts the extensions to let them stop cleanly, and also removes the environment. Lambda sends a Shutdown event to each extension, which tells the extension that the environment is about to be shut down.

The Init phase is followed by one or further function invocations. When there are no invocation requests, Lambda initiates the SHutdown phase.

Each phase starts with an event that Lambda sends to the runtime and to all registered extensions. The runtime and each extension indicate completion by sending a Next API request. Lambda freezes the execution environment when the runtime and each extension have completed and there are no pending events.

  • Init phase
  • Invoke phase
  • Shutdown phase

    Init phase

    In the Init phase, Lambda performs three tasks
  • Start all extensions( Extension init>
  • Bootstrap the runtime( Runtime init>
    Run the function's static code( Function init>


  • The Init phase ends when the runtime and all extensions signal that they're ready by sending a Next API request. The Init phase is limited to 10seconds.However, Lambda retries the Init phase at the time of the first function invocation, If all three tasks don't complete within 10 seconds.

    Invoke phase

    When a Lambda function is invoked in response to a Next API request, Lambda sends an Invoke event to the runtime and to each extension.

    The function's timeout setting limits the duration of the entire Invoke phase. For illustration, if you set the function timeout as 360 seconds, the function and all extensions need to complete within 360 seconds. Note that there's no independentpost-invoke phase. The duration is the sum of all invocation time( runtime extensions>
    and isn't calculated until the function and all extensions have finished executing.

    The bring phase ends after the runtime and all extensions signal that they're done by sending a Next API request.

    However, Lambda resets the execution environment, If the Lambda function crashes or times out during the Invoke phase. The reset behaves like a Shutdown event. First, Lambda shuts down the runtime. also Lambda sends a Shutdown event to each registered external extension. The event includes the reason for theshutdown.However, Lambda initializes the runtime and extensions as part of the next invocation, If another Invoke event results in this execution environment being reused.

    Shutdown phase

    When Lambda is about to shut down the runtime, it sends a Shutdown event to each registered external extension. Extensions can use this time for final cleanup tasks. The Shutdown event is a response to a Next API request.

    Duration The entire Shutdown phase is limited at 2seconds.However, Lambda terminates it via a signal( SIGKILL>
    , If the runtime or any extension doesn't respond.

    After the function and all extensions have completed, Lambda maintains the execution environment for some time in expectation of another function invocation. In effect, Lambda freezes the execution environment. When the function is invoked again, Lambda thaws the environment for reuse. Reusing the execution environment has the following implications

    Objects declared outside of the function's handler method remain initialized, providing additional optimization when the function is invoked again. For illustration, if your Lambda function establishes a database connection, rather of reestablishing the connection, the original connection is used in subsequent invocations. We recommend adding logic in your code to check if a connection exists before creating a new one.

    Each execution environment provides 512 MB and,240 MB, in 1- MB increments, of disk space in the/ tmp directory. The directory content remains when the execution environment is frozen, providing a transient cache that can be used for multiple conjurations. You can add extra law to check if the cache has the data that you stored. For further information on deployment size limits, see Lambda quotas.

    Background processes or callbacks that were initiated by your Lambda function and didn't complete when the function ended resume if Lambda reuses the execution environment. Make sure that any background processes or callbacks in your code are complete before the code exits.

    When you write your function code, don't assume that Lambda automatically reuses the execution environment for subsequent function invocations. Other factors may dictate a need for Lambda to create a new execution environment, which can lead to unexpected results, similar as database connection failures.