🔌 AWS Lambda Executor#


With this executor, users can execute tasks (electrons) or entire lattices using the AWS Lambda serverless compute service. It is appropriate to use this plugin for electrons that are expected to be short lived, low in compute intensity. This plugin can also be used for workflows with a high number of electrons that are embarassingly parallel aka fully independent of each other.

The AWS resources required by this executor are quite minimal 1) S3 bucket for caching objects 2) Container based AWS lambda function 3) IAM role for the Lambda.

The following snippet shows the required terraform to spin up the necessary resources and can be used as a base template

1. Installation#

To use this plugin with Covalent, simply install it using pip:

pip install covalent-awslambda-plugin


Due to the isolated nature of AWS Lambda, the packages available on that environment are limited. This means that only the modules that come with python out-of-the-box are accessible to your function. Deps are also limited in a similar fashion. However, AWS does provide a workaround for pip package installations: https://aws.amazon.com/premiumsupport/knowledge-center/lambda-python-package-compatible/.

2. Usage Example#

This is an example of how a workflow can be constructed to use the AWS Lambda executor. In the example, we join two words to form a phrase and return an excited phrase.

import covalent as ct
from covalent.executor import AWSLambdaExecutor

executor = AWSLambdaExecutor(
    function_name = "my-lambda-function"

def join_words(a, b):
    return ",".join([a, b])

def excitement(a):
    return f"{a}!"

def simple_workflow(a, b):
    phrase = join_words(a, b)
    return excitement(phrase)

dispatch_id = ct.dispatch(simple_workflow)("Hello", "World")
result = ct.get_result(dispatch_id, wait=True)


During the execution of the workflow, one can navigate to the UI to see the status of the workflow. Once completed, the above script should also output the result:

Hello, World!

In order for the above workflow to run successfully, one has to provision the required AWS resources as mentioned in 4. Required AWS Resources.


Users may encounter failures with dispatching workflows on MacOS due to errors with importing the psutil module. This is a known issue and will be addressed in a future sprint.

3. Overview of configuration#

The following table shows a list of all input arguments including the required arguments to be supplied when instantiating the executor:


Config Value

Is Required






Name of the AWS lambda function to be used at runtime




Name of an AWS S3 bucket that the executor must use to cache object files




The path to your AWS credentials file




AWS profile used for authentication




Time interval between successive polls to the lambda function




Path on the local file system to a cache




Duration in seconds to keep polling the task for results/exceptions raised

The following snippet shows how users may modify their Covalent configuration to provide the necessary input arguments to the executor:

function_name = "my-lambda-function"
s3_bucket_name = "covalent-lambda-job-resources"
credentials_file = "/home/<user>/.aws/credentials"
profile = "default"
region = "us-east-1"
cache_dir = "/home/<user>/.cache/covalent"
poll_freq = 5
timeout = 60

Within a workflow, users can use this executor with the default values configured in the configuration file as follows:

import covalent as ct

def task(x, y):
    return x + y

Alternatively, users can customize this executor entirely by providing their own values to its constructor as follows:

import covalent as ct
from covalent.executor import AWSLambdaExecutor

lambda_executor = AWSLambdaExecutor(
    function_name = "my-lambda-function"

def task(x, y):
    return x + y

4. Required AWS Resources#

In order for the executor to work end-to-end, the following resources need to be configured either with Terraform or manually provisioned on the AWS Dashboard:



Config Name


IAM Role


The IAM role this lambda will assume during execution of your tasks

S3 Bucket


Name of an AWS S3 bucket that the executor can use to store temporary files

AWS Lambda function


Name of the AWS lambda function created in AWS

The following JSON policy document shows the necessary IAM permissions required for the executor to properly run tasks using the AWS Lambda compute service:

where <bucket-name> is the name of an S3 bucket to be used by the executor to store temporary files generated during task execution. The lambda function interacts with the S3 bucket as well as with the AWS Cloudwatch service to route any log messages. Due to this, the lambda function must have the necessary IAM permissions in order to do so. Users must provision an IAM role that has the AWSLambdaExecute policy attached to it. The policy document is summarized here for convenience:

Users can use the following Terraform snippet as a starting point to spin up the required resources

provider aws {}

resource aws_s3_bucket bucket {

resource aws_iam_role lambda_iam {
    name = var.aws_lambda_iam_role_name
    assume_role_policy = jsonencode({
        Version = "2012-10-17"
        Statement = [
                Action = "sts:AssumeRole"
                Effect = "Allow"
                Sid    = ""
                Principal = {
                    Service = "lambda.amazonaws.com"
    managed_policy_arns = [ "arn:aws:iam::aws:policy/AWSLambdaExecute" ]

resource aws_lambda_function lambda {
    function_name = "my-lambda-function"
    role = aws_iam_role.lambda_iam.arn
    packge_type = "Image"
    timeout = <timeout value in seconds, max 900 (15 minutes), defaults to 3>
    memory_size = <Max memory in MB that the Lambda is expected to use, defaults to 128>
    image_uri = <URI to the container image used by the lambda, defaults to `public.ecr.aws/covalent/covalent-lambda-executor:stable`>

For more information on how to create IAM roles and attach policies in AWS, refer to IAM roles. For more information on AWS S3, refer to AWS S3.