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#317 in Web programming
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SLoC
AWS CloudFormation Guard as a Lambda
The Lambda version of the tool is a lightweight wrapper around the core cfn-guard code that can simply be invoked as a Lambda. We currently support 2 methods for deploying the Lambda.
Table of Contents
- Method 1: Installation using AWS CLI
- Method 2: Installation using SAM CLI
- Calling the AWS Lambda Function
- FAQs
Method 1: Installation using AWS CLI
Dependencies
- AWS CLI configured with permissions to deploy and invoke Lambdas
- Rust (See the installation instructions in the top-level README)
- If building on a Mac, you'll need Homebrew.
- If building on Ubuntu, you'll need to run
sudo apt-get update; sudo apt install build-essential
if you haven't already - If building on CentOS/RHEL you'll need to add the
musl-libc
package repository to your yum config (see https://copr.fedorainfracloud.org/coprs/ngompa/musl-libc/)
Mac/Ubuntu
- Install and configure the dependencies.
- Run
rustup target add x86_64-unknown-linux-musl
. - If you're on a Mac, add the following to
~/.cargo/config
:[target.x86_64-unknown-linux-musl] linker = "x86_64-linux-musl-gcc"
- Ensure you're in the
guard-lambda
directory. - Run
cargo build --release --target x86_64-unknown-linux-musl
. For a custom runtime, AWS Lambda looks for an executable calledbootstrap
in the deployment package zip. Rename the generatedcfn-lambda
executable tobootstrap
and add it to a zip archive. - Run
cp ./../target/x86_64-unknown-linux-musl/release/cfn-guard-lambda ./bootstrap && zip lambda.zip bootstrap && rm bootstrap
. - Initialize the following shell variables with values corresponding to your account:
LAMBDA_FUNCTION_NAME=CloudFormationGuardLambda AWS_ACCOUNT_ID=111111111111 REGION=us-east-1 ROLE_NAME="${LAMBDA_FUNCTION_NAME}Role"
- Create an execution role for Lambda function. Refer the linked documentation for updated instructions. Alternatively, use the following command:
aws iam create-role \ --role-name $ROLE_NAME \ --assume-role-policy-document '{"Version": "2012-10-17","Statement": [{ "Effect": "Allow", "Principal": {"Service": "lambda.amazonaws.com"}, "Action": "sts:AssumeRole"}]}' aws iam attach-role-policy \ --role-name $ROLE_NAME \ --policy-arn arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
- Run the following command to submit
cfn-guard
as an AWS Lambda function to your account:aws lambda create-function \ --function-name $LAMBDA_FUNCTION_NAME \ --handler guard.handler \ --zip-file fileb://./lambda.zip \ --runtime provided.al2023 \ --role "arn:aws:iam::${AWS_ACCOUNT_ID}:role/${ROLE_NAME}" \ --environment Variables={RUST_BACKTRACE=1} \ --tracing-config Mode=Active \ --region $REGION
Method 2: Installation using SAM CLI
Dependencies
-
SAM CLI installed
-
AWS CLI installed and configured with permissions to deploy via CloudFormation. SAM CLI will internally use the credentials you setup AWS CLI with. You may use the following IAM policy as a reference for least privileged access.
IAM Policy for SAM CLI User
{ "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Action": [ "cloudformation:CreateChangeSet", "cloudformation:CreateStack", "cloudformation:DeleteChangeSet", "cloudformation:DeleteStack", "cloudformation:DescribeChangeSet", "cloudformation:DescribeStackEvents", "cloudformation:DescribeStackResource", "cloudformation:DescribeStackResources", "cloudformation:DescribeStacks", "cloudformation:ExecuteChangeSet", "cloudformation:GetTemplate", "cloudformation:GetTemplateSummary", "cloudformation:ListStackResources", "cloudformation:SetStackPolicy", "cloudformation:UpdateStack", "cloudformation:UpdateTerminationProtection", "iam:AttachRolePolicy", "iam:CreateRole", "iam:DeleteRole", "iam:DetachRolePolicy", "iam:GetRole", "iam:PassRole", "lambda:CreateFunction", "lambda:DeleteFunction", "lambda:GetFunction", "lambda:TagResource", "s3:GetObject", "s3:PutObject" ], "Resource": "*" } ] }
-
Docker installed
Building and deploying
- Make sure docker is running
- Navigate to
guard-lambda
directory and runsam build --use-container
to build the code for the Lambda function - Run
sam deploy --guided
and complete the interactive workflow. This workflow will create a CloudFormation changeset and deploy it - Once it succeeds, the name of the function will be shown in the
CloudFormationGuardLambdaFunctionName
output - For subsequent updates, build the code again (step 2) and run
sam deploy
(without--guided
)
Calling the AWS Lambda Function
Payload Structure
The payload JSON to cfn-guard-lambda
requires the following two fields:
data
- (Mandatory, string) Infrastructure as code template data in YAML or JSON structure.rules
- (Mandatory, list of strings) List of rules that you want to run your YAML or JSON structured data against.verbose
- (Optional, boolean) A flag when set tofalse
makes Lambda emit a shorter version of the output. This is set totrue
by default for backward compatibility.
Invoking cfn-guard-lambda
Initialize the variable LAMBDA_FUNCTION_NAME
to the name of the deployed AWS Lambda Function, and invoke it using the following syntax:
aws lambda invoke \
--function-name $LAMBDA_FUNCTION_NAME \
--cli-binary-format raw-in-base64-out \
--payload "{"data": "<input data>", "rules" : ["<input rules 1>", "<input rules 2>", ...], "verbose": <true|false>}" \
output.json
Note: --cli-binary-format
option is only required to override the default configuration setting to perform the parsing of
JSON input. If the command doesn't work with this option, try running it without this configuration override. Your current
AWS CLI version may have this configuration set to the required value.
Example
aws lambda invoke \
--function-name $LAMBDA_FUNCTION_NAME \
--cli-binary-format raw-in-base64-out \
--payload '{"data":"{\"Resources\":{\"NewVolume\":{\"Type\":\"AWS::EC2::Volume\",\"Properties\":{\"Size\":500,\"Encrypted\":true,\"AvailabilityZone\":\"us-west-2b\"}},\"NewVolume2\":{\"Type\":\"AWS::EC2::Volume\",\"Properties\":{\"Size\":50,\"Encrypted\":true,\"AvailabilityZone\":\"us-west-2c\"}}}}","rules":["let ec2_volumes = Resources.*[ Type == /EC2::Volume/ ]\nrule EC2_ENCRYPTION_BY_DEFAULT when %ec2_volumes !empty {\n %ec2_volumes.Properties.Encrypted == true \n <<\n Violation: All EBS Volumes should be encrypted \n Fix: Set Encrypted property to true\n >>\n}"],"verbose":false}' \
output.json
Note: --cli-binary-format
option is only required to override the default configuration setting to perform the parsing of
JSON input. If the command doesn't work with this option, try running it without this configuration override. Your current
AWS CLI version may have this configuration set to the required value.
FAQs
Q: How do I troubleshoot a lambda call returning an opaque error message like:
{"errorType": "Runtime.ExitError", "errorMessage": "RequestId: 1c0c0620-0f83-40bc-8eca-3cf2cf24820f Error: Runtime exited with error: exit status 101"}
A: Run the same rule set and template locally with cfn-guard
to get a better message, such as:
Parsing error handling template file, Error = while parsing a flow mapping, did not find expected ',' or '}' at line 21 column 1
cfn-guard-lambda
is just a wrapper for the cfn-guard
code and each can be used to test the other.
Dependencies
~20–31MB
~524K SLoC