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Idempotency

The idempotency utility provides a simple solution to convert your Lambda functions into idempotent operations which are safe to retry.

Key features

  • Prevent Lambda handler function from executing more than once on the same event payload during a time window
  • Ensure Lambda handler returns the same result when called with the same payload
  • Select a subset of the event as the idempotency key using JMESPath expressions
  • Set a time window in which records with the same payload should be considered duplicates
  • Expires in-progress executions if the Lambda function times out halfway through

Terminology

The property of idempotency means that an operation does not cause additional side effects if it is called more than once with the same input parameters.

Idempotent operations will return the same result when they are called multiple times with the same parameters. This makes idempotent operations safe to retry. Read more about idempotency.

Idempotency key is a hash representation of either the entire event or a specific configured subset of the event, and invocation results are JSON serialized and stored in your persistence storage layer.

Idempotency record is the data representation of an idempotent request saved in your preferred storage layer. We use it to coordinate whether a request is idempotent, whether it's still valid or expired based on timestamps, etc.

classDiagram
    direction LR
    class DataRecord {
        string IdempotencyKey
        DataRecordStatus Status
        long ExpiryTimestamp
        long InProgressExpiryTimestamp
        string ResponseData
        string PayloadHash
    }
    class Status {
        <<Enum>>
        INPROGRESS
        COMPLETED
        EXPIRED
    }
    DataRecord -- Status
Idempotency record representation

Getting started

Installation

You should install with NuGet:

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Install-Package AWS.Lambda.Powertools.Idempotency

Or via the .NET Core command line interface:

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dotnet add package AWS.Lambda.Powertools.Idempotency

IAM Permissions

Your Lambda function IAM Role must have dynamodb:GetItem, dynamodb:PutItem, dynamodb:UpdateItem and dynamodb:DeleteItem IAM permissions before using this feature.

Note

If you're using our example AWS Serverless Application Model (SAM), AWS Cloud Development Kit (CDK), or Terraform it already adds the required permissions.

Required resources

Before getting started, you need to create a persistent storage layer where the idempotency utility can store its state - your Lambda functions will need read and write access to it.

As of now, Amazon DynamoDB is the only supported persistent storage layer, so you'll need to create a table first.

Default table configuration

If you're not changing the default configuration for the DynamoDB persistence layer, this is the expected default configuration:

Configuration Value Notes
Partition key id
TTL attribute name expiration This can only be configured after your table is created if you're using AWS Console

Tip: You can share a single state table for all functions

You can reuse the same DynamoDB table to store idempotency state. We add your function name in addition to the idempotency key as a hash key.

AWS Serverless Application Model (SAM) example
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Resources:
IdempotencyTable:
    Type: AWS::DynamoDB::Table
    Properties:
    AttributeDefinitions:
        - AttributeName: id
        AttributeType: S
    KeySchema:
        - AttributeName: id
        KeyType: HASH
    TimeToLiveSpecification:
        AttributeName: expiration
        Enabled: true
    BillingMode: PAY_PER_REQUEST

IdempotencyFunction:
    Type: AWS::Serverless::Function
    Properties:
    CodeUri: Function
    Handler: HelloWorld::HelloWorld.Function::FunctionHandler
    Policies:
        - DynamoDBCrudPolicy:
            TableName: !Ref IdempotencyTable
    Environment:
        Variables:
        IDEMPOTENCY_TABLE: !Ref IdempotencyTable

Warning: Large responses with DynamoDB persistence layer

When using this utility with DynamoDB, your function's responses must be smaller than 400KB. Larger items cannot be written to DynamoDB and will cause exceptions.

Info: DynamoDB

Each function invocation will generally make 2 requests to DynamoDB. If the result returned by your Lambda is less than 1kb, you can expect 2 WCUs per invocation. For retried invocations, you will see 1WCU and 1RCU. Review the DynamoDB pricing documentation to estimate the cost.

Idempotent attribute

You can quickly start by configuring Idempotency and using it with the Idempotent attribute on your Lambda function.

Important

Initialization and configuration of the Idempotency must be performed outside the handler, preferably in the constructor.

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public class Function
{
    public Function()
    {
        Idempotency.Configure(builder => builder.UseDynamoDb("idempotency_table"));
    }

    [Idempotent]
    public Task<string> FunctionHandler(string input, ILambdaContext context)
    {
        return Task.FromResult(input.ToUpper());
    }
}

Idempotent attribute on another method

You can use the Idempotent attribute for any .NET function, not only the Lambda handlers.

When using Idempotent attribute on another method, you must tell which parameter in the method signature has the data we should use:

  • If the method only has one parameter, it will be used by default.
  • If there are 2 or more parameters, you must set the IdempotencyKey attribute on the parameter to use.

The parameter must be serializable in JSON. We use System.Text.Json internally to (de)serialize objects

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public class Function
{
    public Function()
    {
        Idempotency.Configure(builder => builder.UseDynamoDb("idempotency_table"));
    }

    public Task<string> FunctionHandler(string input, ILambdaContext context)
    {
        MyInternalMethod("hello", "world")
        return Task.FromResult(input.ToUpper());
    }

    [Idempotent]
    private string MyInternalMethod(string argOne, [IdempotencyKey] string argTwo) {
        return "something";
    }
}

Choosing a payload subset for idempotency

Tip: Dealing with always changing payloads

When dealing with an elaborate payload (API Gateway request for example), where parts of the payload always change, you should configure the EventKeyJmesPath.

Use IdempotencyConfig to instruct the Idempotent annotation to only use a portion of your payload to verify whether a request is idempotent, and therefore it should not be retried.

Payment scenario

In this example, we have a Lambda handler that creates a payment for a user subscribing to a product. We want to ensure that we don't accidentally charge our customer by subscribing them more than once.

Imagine the function executes successfully, but the client never receives the response due to a connection issue. It is safe to retry in this instance, as the idempotent decorator will return a previously saved response.

What we want here is to instruct Idempotency to use user_id and product_id fields from our incoming payload as our idempotency key. If we were to treat the entire request as our idempotency key, a simple HTTP header change would cause our customer to be charged twice.

Deserializing JSON strings in payloads for increased accuracy.

The payload extracted by the EventKeyJmesPath is treated as a string by default, so will be sensitive to differences in whitespace even when the JSON payload itself is identical.

To alter this behaviour, you can use the JMESPath built-in function powertools_json() to treat the payload as a JSON object rather than a string.

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Idempotency.Configure(builder =>
        builder
            .WithOptions(optionsBuilder =>
                optionsBuilder.WithEventKeyJmesPath("powertools_json(Body).[\"user_id\", \"product_id\"]"))
            .UseDynamoDb("idempotency_table"));

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{
"version": "2.0",
"routeKey": "ANY /createpayment",
"rawPath": "/createpayment",
"rawQueryString": "",
"headers": {
"Header1": "value1",
"Header2": "value2"
},
"requestContext": {
"accountId": "123456789012",
"apiId": "api-id",
"domainName": "id.execute-api.us-east-1.amazonaws.com",
"domainPrefix": "id",
"http": {
"method": "POST",
"path": "/createpayment",
"protocol": "HTTP/1.1",
"sourceIp": "ip",
"userAgent": "agent"
},
"requestId": "id",
"routeKey": "ANY /createpayment",
"stage": "$default",
"time": "10/Feb/2021:13:40:43 +0000",
"timeEpoch": 1612964443723
},
"body": "{\"user_id\":\"xyz\",\"product_id\":\"123456789\"}",
"isBase64Encoded": false
}

Lambda timeouts

Note

This is automatically done when you decorate your Lambda handler with Idempotent attribute.

To prevent against extended failed retries when a Lambda function times out, Powertools for AWS Lambda (.NET) calculates and includes the remaining invocation available time as part of the idempotency record.

Example

If a second invocation happens after this timestamp, and the record is marked as INPROGRESS, we will execute the invocation again as if it was in the EXPIRED state (e.g, Expired field elapsed).

This means that if an invocation expired during execution, it will be quickly executed again on the next retry.

Important

If you are only using the Idempotent attribute to guard isolated parts of your code, you must use RegisterLambdaContext available in the Idempotency static class to benefit from this protection.

Here is an example on how you register the Lambda context in your handler:

Registering the Lambda context
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public class Function
{
    public Function()
    {
        Idempotency.Configure(builder => builder.UseDynamoDb("idempotency_table"));
    }

    public Task<string> FunctionHandler(string input, ILambdaContext context)
    {
        Idempotency.RegisterLambdaContext(context);
        MyInternalMethod("hello", "world")
        return Task.FromResult(input.ToUpper());
    }

    [Idempotent]
    private string MyInternalMethod(string argOne, [IdempotencyKey] string argTwo) {
        return "something";
    }
}

Handling exceptions

If you are using the Idempotent attribute on your Lambda handler or any other method, any unhandled exceptions that are thrown during the code execution will cause the record in the persistence layer to be deleted. This means that new invocations will execute your code again despite having the same payload. If you don't want the record to be deleted, you need to catch exceptions within the idempotent function and return a successful response.

Warning

We will throw an IdempotencyPersistenceLayerException if any of the calls to the persistence layer fail unexpectedly.

As this happens outside the scope of your decorated function, you are not able to catch it.

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    Client->>Lambda: Invoke (event)
    Lambda->>Persistence Layer: Get or set (id=event.search(payload))
    activate Persistence Layer
    Note right of Persistence Layer: Locked during this time. Prevents multiple<br/>Lambda invocations with the same<br/>payload running concurrently.
    Lambda--xLambda: Call handler (event).<br/>Raises exception
    Lambda->>Persistence Layer: Delete record (id=event.search(payload))
    deactivate Persistence Layer
    Lambda-->>Client: Return error response
Idempotent sequence exception

If you are using Idempotent attribute on another method, any unhandled exceptions that are raised inside the decorated function will cause the record in the persistence layer to be deleted, and allow the function to be executed again if retried.

If an Exception is raised outside the scope of the decorated method and after your method has been called, the persistent record will not be affected. In this case, idempotency will be maintained for your decorated function. Example:

Exception not affecting idempotency record sample
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public class Function
{
    public Function()
    {
        Idempotency.Configure(builder => builder.UseDynamoDb("idempotency_table"));
    }

    public Task<string> FunctionHandler(string input, ILambdaContext context)
    {
        Idempotency.RegisterLambdaContext(context);
        // If an exception is thrown here, no idempotent record will ever get created as the
        // idempotent method does not get called

        MyInternalMethod("hello", "world")

        // This exception will not cause the idempotent record to be deleted, since it
        // happens after the decorated method has been successfully called    
        throw new Exception();
    }

    [Idempotent]
    private string MyInternalMethod(string argOne, [IdempotencyKey] string argTwo) {
        return "something";
    }
}

Idempotency request flow

The following sequence diagrams explain how the Idempotency feature behaves under different scenarios.

Successful request

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    alt initial request
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Prevents concurrent invocations <br> with the same payload
        Lambda-->>Lambda: Call your function
        Lambda->>Persistence Layer: Update record with result
        deactivate Persistence Layer
        Persistence Layer-->>Persistence Layer: Update record
        Note over Lambda,Persistence Layer: Set record status to COMPLETE. <br> New invocations with the same payload <br> now return the same result
        Lambda-->>Client: Response sent to client
    else retried request
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Persistence Layer-->>Lambda: Already exists in persistence layer.
        deactivate Persistence Layer
        Note over Lambda,Persistence Layer: Record status is COMPLETE and not expired
        Lambda-->>Client: Same response sent to client
    end
Idempotent successful request

Successful request with cache enabled

In-memory cache is disabled by default.

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    alt initial request
      Client->>Lambda: Invoke (event)
      Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
      activate Persistence Layer
      Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Prevents concurrent invocations <br> with the same payload
      Lambda-->>Lambda: Call your function
      Lambda->>Persistence Layer: Update record with result
      deactivate Persistence Layer
      Persistence Layer-->>Persistence Layer: Update record
      Note over Lambda,Persistence Layer: Set record status to COMPLETE. <br> New invocations with the same payload <br> now return the same result
      Lambda-->>Lambda: Save record and result in memory
      Lambda-->>Client: Response sent to client
    else retried request
      Client->>Lambda: Invoke (event)
      Lambda-->>Lambda: Get idempotency_key=hash(payload)
      Note over Lambda,Persistence Layer: Record status is COMPLETE and not expired
      Lambda-->>Client: Same response sent to client
    end
Idempotent successful request cached

Expired idempotency records

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    alt initial request
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Prevents concurrent invocations <br> with the same payload
        Lambda-->>Lambda: Call your function
        Lambda->>Persistence Layer: Update record with result
        deactivate Persistence Layer
        Persistence Layer-->>Persistence Layer: Update record
        Note over Lambda,Persistence Layer: Set record status to COMPLETE. <br> New invocations with the same payload <br> now return the same result
        Lambda-->>Client: Response sent to client
    else retried request
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Persistence Layer-->>Lambda: Already exists in persistence layer.
        deactivate Persistence Layer
        Note over Lambda,Persistence Layer: Record status is COMPLETE but expired hours ago
        loop Repeat initial request process
            Note over Lambda,Persistence Layer: 1. Set record to INPROGRESS, <br> 2. Call your function, <br> 3. Set record to COMPLETE
        end
        Lambda-->>Client: Same response sent to client
    end
Previous Idempotent request expired

Concurrent identical in-flight requests

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    Client->>Lambda: Invoke (event)
    Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
    activate Persistence Layer
    Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Prevents concurrent invocations <br> with the same payload
      par Second request
          Client->>Lambda: Invoke (event)
          Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
          Lambda--xLambda: IdempotencyAlreadyInProgressError
          Lambda->>Client: Error sent to client if unhandled
      end
    Lambda-->>Lambda: Call your function
    Lambda->>Persistence Layer: Update record with result
    deactivate Persistence Layer
    Persistence Layer-->>Persistence Layer: Update record
    Note over Lambda,Persistence Layer: Set record status to COMPLETE. <br> New invocations with the same payload <br> now return the same result
    Lambda-->>Client: Response sent to client
Concurrent identical in-flight requests

Lambda request timeout

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    alt initial request
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Prevents concurrent invocations <br> with the same payload
        Lambda-->>Lambda: Call your function
        Note right of Lambda: Time out
        Lambda--xLambda: Time out error
        Lambda-->>Client: Return error response
        deactivate Persistence Layer
    else retry after Lambda timeout elapses
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Reset in_progress_expiry attribute
        Lambda-->>Lambda: Call your function
        Lambda->>Persistence Layer: Update record with result
        deactivate Persistence Layer
        Persistence Layer-->>Persistence Layer: Update record
        Lambda-->>Client: Response sent to client
    end
Idempotent request during and after Lambda timeouts

Optional idempotency key

sequenceDiagram
    participant Client
    participant Lambda
    participant Persistence Layer
    alt request with idempotency key
        Client->>Lambda: Invoke (event)
        Lambda->>Persistence Layer: Get or set idempotency_key=hash(payload)
        activate Persistence Layer
        Note over Lambda,Persistence Layer: Set record status to INPROGRESS. <br> Prevents concurrent invocations <br> with the same payload
        Lambda-->>Lambda: Call your function
        Lambda->>Persistence Layer: Update record with result
        deactivate Persistence Layer
        Persistence Layer-->>Persistence Layer: Update record
        Note over Lambda,Persistence Layer: Set record status to COMPLETE. <br> New invocations with the same payload <br> now return the same result
        Lambda-->>Client: Response sent to client
    else request(s) without idempotency key
        Client->>Lambda: Invoke (event)
        Note over Lambda: Idempotency key is missing
        Note over Persistence Layer: Skips any operation to fetch, update, and delete
        Lambda-->>Lambda: Call your function
        Lambda-->>Client: Response sent to client
    end
Optional idempotency key

Advanced

Persistence stores

DynamoDBPersistenceStore

This persistence store is built-in, and you can either use an existing DynamoDB table or create a new one dedicated for idempotency state (recommended).

Use the builder to customize the table structure:

Customizing DynamoDBPersistenceStore to suit your table structure
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new DynamoDBPersistenceStoreBuilder()
    .WithTableName("TABLE_NAME")
    .WithKeyAttr("idempotency_key")
    .WithExpiryAttr("expires_at")
    .WithStatusAttr("current_status")
    .WithDataAttr("result_data")
    .WithValidationAttr("validation_key")
    .WithInProgressExpiryAttr("in_progress_expires_at")
    .Build()

When using DynamoDB as a persistence layer, you can alter the attribute names by passing these parameters when initializing the persistence layer:

Parameter Required Default Description
TableName Y Table name to store state
KeyAttr id Partition key of the table. Hashed representation of the payload (unless SortKeyAttr is specified)
ExpiryAttr expiration Unix timestamp of when record expires
InProgressExpiryAttr in_progress_expiration Unix timestamp of when record expires while in progress (in case of the invocation times out)
StatusAttr status Stores status of the Lambda execution during and after invocation
DataAttr data Stores results of successfully idempotent methods
ValidationAttr validation Hashed representation of the parts of the event used for validation
SortKeyAttr Sort key of the table (if table is configured with a sort key).
StaticPkValue idempotency#{LAMBDA_FUNCTION_NAME} Static value to use as the partition key. Only used when SortKeyAttr is set.

Customizing the default behavior

Idempotency behavior can be further configured with IdempotencyOptions using a builder:

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new IdempotencyOptionsBuilder()
    .WithEventKeyJmesPath("id")
    .WithPayloadValidationJmesPath("paymentId")
    .WithThrowOnNoIdempotencyKey(true)
    .WithExpiration(TimeSpan.FromMinutes(1))
    .WithUseLocalCache(true)
    .WithHashFunction("MD5")
    .Build();

These are the available options for further configuration:

Parameter Default Description
EventKeyJMESPath "" JMESPath expression to extract the idempotency key from the event record.
PayloadValidationJMESPath "" JMESPath expression to validate whether certain parameters have changed in the event
ThrowOnNoIdempotencyKey False Throw exception if no idempotency key was found in the request
ExpirationInSeconds 3600 The number of seconds to wait before a record is expired
UseLocalCache false Whether to locally cache idempotency results (LRU cache)
HashFunction MD5 Algorithm to use for calculating hashes, as supported by System.Security.Cryptography.HashAlgorithm (eg. SHA1, SHA-256, ...)

These features are detailed below.

Handling concurrent executions with the same payload

This utility will throw an IdempotencyAlreadyInProgressException if we receive multiple invocations with the same payload while the first invocation hasn't completed yet.

Info

If you receive IdempotencyAlreadyInProgressException, you can safely retry the operation.

This is a locking mechanism for correctness. Since we don't know the result from the first invocation yet, we can't safely allow another concurrent execution.

Using in-memory cache

By default, in-memory local caching is disabled, to avoid using memory in an unpredictable way.

Warning

Be sure to configure the Lambda memory according to the number of records and the potential size of each record.

You can enable it as seen before with:

Enable local cache
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    new IdempotencyOptionsBuilder()
        .WithUseLocalCache(true)
        .Build()
When enabled, we cache a maximum of 255 records in each Lambda execution environment

Note: This in-memory cache is local to each Lambda execution environment

This means it will be effective in cases where your function's concurrency is low in comparison to the number of "retry" invocations with the same payload, because cache might be empty.

Expiring idempotency records

Note

By default, we expire idempotency records after an hour (3600 seconds).

In most cases, it is not desirable to store the idempotency records forever. Rather, you want to guarantee that the same payload won't be executed within a period of time.

You can change this window with the ExpirationInSeconds parameter:

Customizing expiration time
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new IdempotencyOptionsBuilder()
    .WithExpiration(TimeSpan.FromMinutes(5))
    .Build()

Records older than 5 minutes will be marked as expired, and the Lambda handler will be executed normally even if it is invoked with a matching payload.

Note: DynamoDB time-to-live field

This utility uses expiration as the TTL field in DynamoDB, as demonstrated in the SAM example earlier.

Payload validation

Question: What if your function is invoked with the same payload except some outer parameters have changed?

Example: A payment transaction for a given productID was requested twice for the same customer, however the amount to be paid has changed in the second transaction.

By default, we will return the same result as it returned before, however in this instance it may be misleading; we provide a fail fast payload validation to address this edge case.

With PayloadValidationJMESPath, you can provide an additional JMESPath expression to specify which part of the event body should be validated against previous idempotent invocations

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Idempotency.Configure(builder =>
        builder
            .WithOptions(optionsBuilder =>
                optionsBuilder
                    .WithEventKeyJmesPath("[userDetail, productId]")
                    .WithPayloadValidationJmesPath("amount"))
            .UseDynamoDb("TABLE_NAME"));

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{
    "userDetail": {
        "username": "User1",
        "user_email": "user@example.com"
    },
    "productId": 1500,
    "charge_type": "subscription",
    "amount": 500
}

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{
    "userDetail": {
        "username": "User1",
        "user_email": "user@example.com"
    },
    "productId": 1500,
    "charge_type": "subscription",
    "amount": 1
}

In this example, the userDetail and productId keys are used as the payload to generate the idempotency key, as per EventKeyJMESPath parameter.

Note

If we try to send the same request but with a different amount, we will raise IdempotencyValidationException.

Without payload validation, we would have returned the same result as we did for the initial request. Since we're also returning an amount in the response, this could be quite confusing for the client.

By using withPayloadValidationJMESPath("amount"), we prevent this potentially confusing behavior and instead throw an Exception.

Making idempotency key required

If you want to enforce that an idempotency key is required, you can set ThrowOnNoIdempotencyKey to True.

This means that we will throw IdempotencyKeyException if the evaluation of EventKeyJMESPath is null.

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public App() 
{
  Idempotency.Configure(builder =>
        builder
            .WithOptions(optionsBuilder =>
                optionsBuilder
                    // Requires "user"."uid" and "orderId" to be present
                    .WithEventKeyJmesPath("[user.uid, orderId]")
                    .WithThrowOnNoIdempotencyKey(true))
            .UseDynamoDb("TABLE_NAME"));
}

[Idempotent]
public Task<OrderResult> FunctionHandler(Order input, ILambdaContext context)
{
  // ...
}

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{
    "user": {
        "uid": "BB0D045C-8878-40C8-889E-38B3CB0A61B1",
        "name": "Foo"
    },
    "orderId": 10000
}

Notice that orderId is now accidentally within user key

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{
    "user": {
        "uid": "DE0D000E-1234-10D1-991E-EAC1DD1D52C8",
        "name": "Joe Bloggs",
        "orderId": 10000
    },
}

Customizing DynamoDB configuration

When creating the DynamoDBPersistenceStore, you can set a custom AmazonDynamoDBClient if you need to customize the configuration:

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public Function()
{
    AmazonDynamoDBClient customClient = new AmazonDynamoDBClient(RegionEndpoint.APSouth1);

    Idempotency.Configure(builder => 
        builder.UseDynamoDb(storeBuilder => 
            storeBuilder.
                WithTableName("TABLE_NAME")
                .WithDynamoDBClient(customClient)
        ));
}

Using a DynamoDB table with a composite primary key

When using a composite primary key table (hash+range key), use SortKeyAttr parameter when initializing your persistence store.

With this setting, we will save the idempotency key in the sort key instead of the primary key. By default, the primary key will now be set to idempotency#{LAMBDA_FUNCTION_NAME}.

You can optionally set a static value for the partition key using the StaticPkValue parameter.

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Idempotency.Configure(builder => 
    builder.UseDynamoDb(storeBuilder => 
        storeBuilder.
            WithTableName("TABLE_NAME")
            .WithSortKeyAttr("sort_key")
    ));

Data would then be stored in DynamoDB like this:

id sort_key expiration status data
idempotency#MyLambdaFunction 1e956ef7da78d0cb890be999aecc0c9e 1636549553 COMPLETED {"id": 12391, "message": "success"}
idempotency#MyLambdaFunction 2b2cdb5f86361e97b4383087c1ffdf27 1636549571 COMPLETED {"id": 527212, "message": "success"}
idempotency#MyLambdaFunction f091d2527ad1c78f05d54cc3f363be80 1636549585 IN_PROGRESS

Testing your code

The idempotency utility provides several routes to test your code.

Disabling the idempotency utility

When testing your code, you may wish to disable the idempotency logic altogether and focus on testing your business logic. To do this, you can set the environment variable POWERTOOLS_IDEMPOTENCY_DISABLED to true.

Extra resources

If you're interested in a deep dive on how Amazon uses idempotency when building our APIs, check out this article.