How to Run Bash Script in AWS Lambda

AWS Lambda is one of the strongest computing services in the serverless domain, via which developers can run their code without the need to provision or manage servers. Writing your code with AWS Lambda is key; AWS takes care of the needed infrastructure for running it. This makes it an excellent choice to build scalable, cost-effective, and highly available applications.

Bash scripting, in UNIX-based systems, is popular automation to undertake different activities. It permits you to run a list of commands into one script; that makes management of the repetitive task much easier and smooth. However, AWS Lambda does not natively support running bash scripts directly. Suppose you need to execute a bash script on an AWS Lambda platform; you can do it using the following workaround.

A supported runtime in a Lambda layer can be used, executing your bash scripts within the AWS Lambda environment. This approach should let you automate a whole range of things from data-processing jobs to system-administration tasks without being required to provision and maintain regular servers. By the end of this article, you will come to know in detail how one can run bash scripts in AWS Lambda and, of course, make the ways of accomplishing tasks automated efficiently inside a serverless environment.

Primary Terminologies

AWS Lambda:

• AWS Lambda is a serverless compute service that runs your code in response to events and automatically manages the underlying compute resources on your behalf, you are billed for only the compute time consumed.

Serverless:

• Serverless is an execution model of cloud computing where a cloud provider dynamically manages the provisioning and allocation of servers. That explains it all for AWS Lambda: the best form of serverless computing.

Bash Script:

• A bash script is a file that contains a series of commands to be run by the Unix shell, which happens to be the Bourne Again Shell. Most commonly, Bash scripts are used to automate repetitive tasks and in system administration.

Layer:

• In AWS Lambda, a layer is an archive for libraries, custom runtimes, or other functions in order to import them into your Lambda function, layers let you manage your function code with its dependencies in a separate unit.

Runtime:

• An AWS Lambda runtime consists of the environment which executes your Lambda Function. It includes the programming language and the required libraries. Commonly used runtime languages are: Python, Node.js, Java, and Ruby.

Deployment Package:

• An AWS Lambda deployment package is a .zip file consisting of your function code along with its dependencies. This is uploaded to AWS Lambda and used as your Lambda function.

Subprocess:

• Subprocess In computing, a subprocess is a process created by another process (the parent process) to perform a specific task. A "subprocess" in the context of AWS Lambda could be executing commands out of a bash script within the Lambda environment.

IAM Role:

• IAM Role is a set of permissions regarding different actions that an entity in AWS can or cannot do. Lambda functions use roles to interact with other services in the AWS securely.

Step-by-Step Process to Run a Bash Script in AWS Lambda

Step 1: Write Your Bash Script

• Create a bash script file, e.g., script.sh, with the commands you want to execute.

Example:

#!/bin/bash
echo "Hello from the GeeksforGeeks!"

• Change permission of bash file to executable

chmod +x script.sh

Step 2: Create a Lambda Layer

Create a Deployment Package:

• AWS Lambda uses deployment packages to store your function code and dependencies. Create a zip file with your bash script and any other necessary files.

  mkdir layer
cp script.sh layer/
cd layer
zip -r my-layer.zip .

• To download zip file from terminal to our desktop or computer use below command

scp -i <.keypair name.pem> ec2-user@<public ip address>:/home/ec2-user/my-lambda-function/my-lambda-function.zip /path/to/local/destination

Publish the Layer:

• Go to the AWS Lambda console.
• Navigate to "Layers" and click "Create layer".

• Upload the my-layer.zip file.

• Provide a name, description, and select a compatible runtime (e.g., Python 3.x, Node.js).

Step 3: Create the Lambda Function

Set up the Lambda Function:

• Go to the AWS Lambda console.
• Click "Create function"
• Choose "Author from scratch".
• Provide a function name, select a runtime (e.g., Python 3.x, Node.js), and click "Create function".

Add the Layer to the Function:

• In your function's configuration, navigate to the "Layers" section. Click on "Add Layer"

• Choose "Custom layers", and select the layer you created in Step 2

Step 4: Modify the Lambda Function Code

• Modify your Lambda function to execute the bash script using the appropriate runtime. For this example, we'll use Python:

import subprocess
import shutil
def lambda_handler(event, context):
    # Copy the script to /tmp directory
    shutil.copyfile("/opt/script.sh", "/tmp/script.sh")
    # Set the executable permission to the script
    subprocess.run(["chmod", "+x", "/tmp/script.sh"])
    # Run the bash script
    result = subprocess.run(["/bin/bash", "/tmp/script.sh"], capture_output=True, text=True)
    return {
        'statusCode': 200,
        'body': result.stdout
    }

Step 5: Test the Lambda Function

• Deploy the function: Click "Deploy" in the AWS Lambda console.

• Create a test event: Go to the "Test" tab, create a new test event with default settings, and click "Test".

• Verify the output: Check the output in the "Execution results". You should see the output of your bash script.

Conclusion

Running a bash script in AWS Lambda is a flexible way to automate any task within a serverless space. Though this is not supported by AWS Lambda natively, this can be achieved with Lambda layers and a runtime supported by it. It's an excellent way to handle repetitive tasks, data processing, and system administration without the overhead of managing servers. We have discussed terms such as AWS Lambda, serverless computing, bash scripts, layers, runtimes, deployment packages, subprocesses, and IAM roles in this document. We also elaborated on a detailed step-by-step approach: how to write your own bash script, creating a Lambda layer, setting up your Lambda function, and making changes in the function code so you can run your script. By following these, you can harness the power of AWS Lambda for running your Bash scripts such that it does refine and enhance your workflows for more automation and fastness. This makes you more competent in many a task without necessarily maintaining conventional server infrastructures, hence bringing productivity with saving cost.