AWS Compute Blog

Getting started with serverless for developers part 5: Sandbox developer account

This is part 5 of the Getting started with serverless series. In part 4, you learn how the developer workflow for building serverless applications differs to a traditional developer workflow. You see how to test business logic locally before deploying to an AWS account.

In this post, you learn how to secure and manage access to your AWS Lambda functions. I show how to invoke Lambda functions in a sandbox developer account directly from an integrated developer environment (IDE) and view output logs in near-real-time. Finally, I show how this helps to test for infrastructure and security configurations before committing changes to the main branch.

A sandbox developer account

Serverless services like Lambda and Amazon API Gateway are pay-per-use, this means developers no longer need to share multiple environments (for example, dev, staging, and production). Instead, every developer can have their own sandboxed AWS developer account. This allows developers to not have to replicate everything to their local environment but rather test with real resources in the cloud.

You can still run code locally during the development of a feature. In post 4, I show how I run Lambda function code locally, using a test harness. This allows me to maintain a fast inner loop, iteratively updating and locally testing code. If my Lambda function interacts with other AWS infrastructure, I deploy them to a sandboxed AWS developer account. This allows me to test my Lambda function code locally while still being able to access managed services in the cloud.

However, it is useful to deploy your function code to a Lambda function in a sandboxed developer account. A sandbox developer account is an AWS account allocated to a developer on a 1:1 basis. It should give developers as much freedom as possible while still protecting resources and budget.

This allows you to test for security configurations and ensure that your Lambda function code behaves as expected when run in the Lambda execution environment:

Creating a sandboxed developer account

The following best practices can help to minimize costs and prevent unauthorized usage.

After creating a sandbox account, it can be useful to associate a named profile with it. A named profile is a collection of credentials that you can apply to an AWS Command Line Interface (AWS CLI) command. When you specify a profile to run a command, the settings and credentials are used to run that command. The AWS CLI supports multiple named profiles that are stored in the config and credentials files.

Configure profiles by adding entries to the config and credentials files. To learn more about named profiles refer to the AWS CLI documentation.

In the following example I configure my credentials file with two named profiles.

The profile named prod is my production account, and the profile named default is my sandbox developer account. The CLI automatically uses the profile named default, if no --profile option is specified in a CLI command.

[default]
aws_access_key_id=AKIAIOSFODNN7EXAMPLE
aws_secret_access_key=wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY

[dev]
aws_access_key_id=AKIAIOSFODNN7EXAMPLE
aws_secret_access_key=wJalBBUtnFEMI/&7MDENG/bPxRfiCYEXAMPLEKEY

[prod]
aws_access_key_id=AKIAI44QH8DHBEXAMPLE
aws_secret_access_key=je7MtGbClwBF/2Zp9Utk/h3yCo8nvbEXAMPLEKEY

AWS Lambda security permissions

AWS Identity and Access Management (IAM) is the service used to manage access to AWS services. Lambda is fully integrated with IAM, allowing you to control precisely what each Lambda function can do within the AWS Cloud. There are two important things that define the scope of permissions in Lambda functions:

The resource policy: Defines which events are authorized to invoke the function.

The execution role policy: Limits what the Lambda function is authorized to do.

Using IAM roles to describe a Lambda function’s permissions, decouples it’s security configuration from the code. This helps reduce the complexity of a lambda function, making it easier to maintain.

A Lambda function’s resource and execution policy should be granted the minimum required permissions for the function to perform it’s task effectively. This is sometimes referred to as the rule of least privilege. As you develop a Lambda function, you expand the scope of this policy to allow access to other resources as required.

When building Lambda-based applications with frameworks such as AWS SAM, you describe both policies in the application’s template.

The following steps show how I deploy and test a Lambda function in a sandbox developer account from within my IDE.

Before you start

All the code relating to this example application can be found in this GitHub repository. To deploy this stage of the application, follow the steps from post 1 to clone the sample application.

  1. Run the following command from the root directory of the cloned repository: 
    cd ./part_5
  2. After creating a sandbox developer account, deploy the example application into it by specifying the corresponding profile name in the AWS SAM CLI command. You can omit this if you named the profile default: 
    sam deploy --config-file ../samconfig.toml  –guided  --profile default

    This produces the following output:

    Make a note of the StarWebhookLambdaFunctionName, you will use this in the following steps.

Logging with serverless applications

After deploying your serverless application to the sandboxed developer account, you need to verify that it’s operating properly. Lambda automatically monitors functions on your behalf, reporting metrics through Amazon CloudWatch. It collects data in the form of logs, metrics, and events and provides a unified view of AWS resources, applications, and services.

To help simplify troubleshooting, the AWS Serverless Application Model CLI (AWS SAM CLI) has a command called sam logs. This command lets you fetch CloudWatch Logs generated by your Lambda function from the command line.

Run the following command in a terminal window to view a live tail of logs generated by the StarWebhookHandler Lambda function. Replace StarWebhookLambdaFunctionName with the Lambda function name generated by your deployment:

sam logs -n StarWebhookLambdaFunctionName --tail

Checking Lambda function permissions in a sandbox developer account

I open a new terminal window and invoke the StarWebhookHandler Lambda function directly from my IDE by running the following AWS SAM CLI command. To invoke the function I pass an example payload located in events/testEvent.json.

aws lambda invoke --function-name <<replace-with-function-name>> \
--payload fileb://events/testEvent.json  \
out.txt

The following screenshot shows my two terminal windows side by side.

The response returned by the CLI command is on the right. The left window shows the tail of logs generated by the Lambda function. I observe that the CLI invocation shows a status 200 response, but the Lambda function logs report an ‘AccessDenied’ error. The function does not have the required permissions to write to Amazon S3.

I edit the Lambda function policy definition, adding permission for my Lambda function to write to an S3 bucket. I run sam build and sam deploy to re-deploy the application to the sandbox developer account. I invoke the Lambda function again. The logs show the following:

  1. The Lambda function responds with “StatusCode 200″.
  2. The Lambda function billed duration, memory size and running duration.
  3. The Lambda function has successfully copied the file to S3

IAM permission errors such as these may not be detected when running the function code locally. This is one of the advantages of deploying and running Lambda functions in a sandboxed developer account while developing an application.

Conclusion

This post explains the advantages of using a sandbox developer account. It shows how to deploy your business logic to a Lambda function in a sandboxed developer account. You are introduced to IAM policies, which control precisely what each Lambda function can do within the AWS Cloud. You learn that CloudWatch provides a unified view of logs for all AWS resources.

Finally, I show how to use the AWS SAM CLI and AWS CLI to invoke a Lambda function in the cloud and view its log output directly from the IDE. This helps to test for security configurations and to ensure that your business logic behaves as expected when run in the Lambda service. Invoking functions and observing their log output directly from your IDE helps to reduce context switching as you build.