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chore(lambda): documentation for SingletonLambda in the README #5996

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Jan 29, 2020
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chore(lambda): documentation for SingletonLambda in the README #5996

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chore(lambda): add documentation for SingletonLambda to README
Jan 28, 2020
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Merge branch 'master' into nija-at/lambda-singletonfunctiondocs
mergify[bot] Jan 29, 2020
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14 changes: 14 additions & 0 deletions packages/@aws-cdk/aws-lambda/README.md
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Expand Up @@ -182,6 +182,20 @@ correct log retention period (never expire, by default).
*Further note* that, if the log group already exists and the `logRetention` is not set, the custom resource will reset
the log retention to never expire even if it was configured with a different value.

### Singleton Function

The `SingletonFunction` construct is a way to guarantee that a lambda function will be guaranteed to be part of the stack,
once and only once, irrespective of how many times the construct is declared to be part of the stack. This is guaranteed
as long as the `uuid` property and the optional `lambdaPurpose` property stay the same whenever they're declared into the
stack.

A typical use case of this function is when a higher level construct needs to declare a Lambda function as part of it but
needs to guarantee that the function is declared once. However, a user of this higher level construct can declare it any
number of times and with different properties. Using `SingletonFunction` here with a fixed `uuid` will guarantee this.

For example, the `LogRetention` construct requires only one single lambda function for all different log groups whose
retention it seeks to manage.

### Language-specific APIs
Language-specific higher level constructs are provided in separate modules:

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6 changes: 4 additions & 2 deletions packages/@aws-cdk/aws-lambda/lib/singleton-lambda.ts
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Expand Up @@ -31,8 +31,10 @@ export interface SingletonFunctionProps extends FunctionProps {
/**
* A Lambda that will only ever be added to a stack once.
*
* The lambda is identified using the value of 'uuid'. Run 'uuidgen'
* for every SingletonLambda you create.
* This construct is a way to guarantee that the lambda function will be guaranteed to be part of the stack,
* once and only once, irrespective of how many times the construct is declared to be part of the stack.
* This is guaranteed as long as the `uuid` property and the optional `lambdaPurpose` property stay the same
* whenever they're declared into the stack.
*
* @resource AWS::Lambda::Function
*/
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