Invoke a Lambda function with Amazon S3 batch events

You can use Amazon S3 batch operations to invoke a Lambda function on a large set of Amazon S3 objects. Amazon S3 tracks the progress of batch operations, sends notifications, and stores a completion report that shows the status of each action.

To run a batch operation, you create an Amazon S3 batch operations job. When you create the job, you provide a manifest (the list of objects) and configure the action to perform on those objects.

When the batch job starts, Amazon S3 invokes the Lambda function synchronously for each object in the manifest. The event parameter includes the names of the bucket and the object.

The following example shows the event that Amazon S3 sends to the Lambda function for an object that is named customerImage1.jpg in the amzn-s3-demo-bucket bucket.

{
"invocationSchemaVersion": "1.0",
    "invocationId": "YXNkbGZqYWRmaiBhc2RmdW9hZHNmZGpmaGFzbGtkaGZza2RmaAo",
    "job": {
        "id": "f3cc4f60-61f6-4a2b-8a21-d07600c373ce"
    },
    "tasks": [
        {
            "taskId": "dGFza2lkZ29lc2hlcmUK",
            "s3Key": "customerImage1.jpg",
            "s3VersionId": "1",
            "s3BucketArn": "arn:aws:s3:::amzn-s3-demo-bucket"
        }
    ]  
}

Your Lambda function must return a JSON object with the fields as shown in the following example. You can copy the invocationId and taskId from the event parameter. You can return a string in the resultString. Amazon S3 saves the resultString values in the completion report.

{
  "invocationSchemaVersion": "1.0",
  "treatMissingKeysAs" : "PermanentFailure",
  "invocationId" : "YXNkbGZqYWRmaiBhc2RmdW9hZHNmZGpmaGFzbGtkaGZza2RmaAo",
  "results": [
    {
      "taskId": "dGFza2lkZ29lc2hlcmUK",
      "resultCode": "Succeeded",
      "resultString": "[\"Alice\", \"Bob\"]"
    }
  ]
}
  

Invoking Lambda functions from Amazon S3 batch operations

You can invoke the Lambda function with an unqualified or qualified function ARN. If you want to use the same function version for the entire batch job, configure a specific function version in the FunctionARN parameter when you create your job. If you configure an alias or the $LATEST qualifier, the batch job immediately starts calling the new version of the function if the alias or $LATEST is updated during the job execution.

Note that you can't reuse an existing Amazon S3 event-based function for batch operations. This is because the Amazon S3 batch operation passes a different event parameter to the Lambda function and expects a return message with a specific JSON structure.

In the resource-based policy that you create for the Amazon S3 batch job, ensure that you set permission for the job to invoke your Lambda function.

In the execution role for the function, set a trust policy for Amazon S3 to assume the role when it runs your function.

If your function uses the AWS SDK to manage Amazon S3 resources, you need to add Amazon S3 permissions in the execution role.

When the job runs, Amazon S3 starts multiple function instances to process the Amazon S3 objects in parallel, up to the concurrency limit of the function. Amazon S3 limits the initial ramp-up of instances to avoid excess cost for smaller jobs.

If the Lambda function returns a TemporaryFailure response code, Amazon S3 retries the operation.

For more information about Amazon S3 batch operations, see Performing batch operations in the Amazon S3 Developer Guide.

For an example of how to use a Lambda function in Amazon S3 batch operations, see Invoking a Lambda function from Amazon S3 batch operations in the Amazon S3 Developer Guide.