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Effortless Updates: How to Automatically Trigger Custom Resources in CloudFormation

Discover how to enhance your AWS CloudFormation deployments by automatically invoking custom resources whenever Lambda function code is updated. This article explores a practical solution using dynamic parameters to streamline workflows and improve automation, ensuring your cloud infrastructure remains agile and up-to-date

cloudformationcdkdevopsiaclambda
Akhil Jain
Published Nov 13, 2024
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AWS CloudFormation is a powerful tool for managing cloud infrastructure as code, enabling teams to define and provision AWS resources in a systematic way. However, one common challenge developers face is the need to update Lambda function code without automatically re-invoking custom resources. By default, CloudFormation does not trigger custom resources unless it detects changes in the template or its parameters. This limitation can lead to outdated configurations and necessitate manual interventions, which can be inefficient and error-prone. To address this issue, a reliable method can be implemented to automatically invoke custom resources whenever Lambda function code is updated within a CloudFormation stack. This approach enhances automation, reduces manual overhead, and ensures that the latest code changes are consistently applied.

Implementing a Dynamic Timestamp Parameter

One effective solution is to introduce a dynamic parameter in the CloudFormation template specifically for the custom resource. By adding a timestamp parameter (e.g., LambdaExecutionTimestamp), developers can ensure that any update to the Lambda function will trigger the execution of the custom resource. Here’s how this can be implemented:
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LambdaExecutionTimestamp:
Type: String
Default: '201906240927' # Example timestamp; this should be updated with each deployment.
Next, the custom resource should be defined using the AWS::CloudFormation::CustomResource type. By referencing the timestamp parameter in the properties of the custom resource, any change to its value will prompt CloudFormation to re-execute the custom resource.
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ExecuteLambda:
Type: AWS::CloudFormation::CustomResource
Properties:
ServiceToken: !GetAtt
- LambdaFunction
- Arn
Timestamp: !Ref LambdaExecutionTimestamp
To ensure that this dynamic parameter is effective, teams should establish a process for updating the LambdaExecutionTimestamp parameter with each deployment. This can be done manually or automated through CI/CD pipelines, ensuring that it always reflects a new value. When using CodePipeline, customers can generate TimeStamp at the time of the build and pass it as parameter to the CloudFormation stack.

Benefits of This Approach

Implementing this solution leads to several significant benefits:
  • Consistent Invocation of Custom Resources: By utilizing a dynamic timestamp parameter, custom resources are invoked every time there is an update to the Lambda function code. This eliminates the need for manual checks and interventions, streamlining the deployment process.
  • Enhanced Automation: This approach minimizes potential errors associated with manual updates and ensures that all resources remain current and properly configured.
  • Improved Deployment Efficiency: The overall deployment process becomes more efficient, allowing teams to push updates confidently. They can be assured that all resources will reflect the latest changes without requiring additional steps.
In conclusion, leveraging dynamic parameters in AWS CloudFormation provides an effective strategy for managing Lambda function updates. This method not only enhances automation but also streamlines workflows, making infrastructure management more efficient and reliable. By adopting such practices, organisations can ensure that their cloud environments remain agile and responsive to changing requirements, ultimately leading to improved operational performance and customer satisfaction.
 
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