Using Lambda with Amazon SQS - AWS Lambda

Using Lambda with Amazon SQS


If you want to send data to a target other than a Lambda function or enrich the data before sending it, see Amazon EventBridge Pipes.

You can use a Lambda function to process messages in an Amazon Simple Queue Service (Amazon SQS) queue. Lambda event source mappings support standard queues and first-in, first-out (FIFO) queues. With Amazon SQS, you can offload tasks from one component of your application by sending them to a queue and processing them asynchronously.

Lambda polls the queue and invokes your Lambda function synchronously with an event that contains queue messages. Lambda reads messages in batches and invokes your function once for each batch. When your function successfully processes a batch, Lambda deletes its messages from the queue.

When Lambda reads a batch, the messages stay in the queue but are hidden for the length of the queue's visibility timeout. If your function successfully processes the batch, Lambda deletes the messages from the queue. By default, if your function encounters an error while processing a batch, all messages in that batch become visible in the queue again. For this reason, your function code must be able to process the same message multiple times without unintended side effects.

To prevent Lambda from processing a message multiple times, you can either configure your event source mapping to include batch item failures in your function response, or you can use the Amazon SQS API action DeleteMessage to remove messages from the queue as your Lambda function successfully processes them. For more information on using the Amazon SQS API, see the Amazon Simple Queue Service API Reference

Example standard queue message event

Example Amazon SQS message event (standard queue)
{ "Records": [ { "messageId": "059f36b4-87a3-44ab-83d2-661975830a7d", "receiptHandle": "AQEBwJnKyrHigUMZj6rYigCgxlaS3SLy0a...", "body": "Test message.", "attributes": { "ApproximateReceiveCount": "1", "SentTimestamp": "1545082649183", "SenderId": "AIDAIENQZJOLO23YVJ4VO", "ApproximateFirstReceiveTimestamp": "1545082649185" }, "messageAttributes": {}, "md5OfBody": "e4e68fb7bd0e697a0ae8f1bb342846b3", "eventSource": "aws:sqs", "eventSourceARN": "arn:aws:sqs:us-east-2:123456789012:my-queue", "awsRegion": "us-east-2" }, { "messageId": "2e1424d4-f796-459a-8184-9c92662be6da", "receiptHandle": "AQEBzWwaftRI0KuVm4tP+/7q1rGgNqicHq...", "body": "Test message.", "attributes": { "ApproximateReceiveCount": "1", "SentTimestamp": "1545082650636", "SenderId": "AIDAIENQZJOLO23YVJ4VO", "ApproximateFirstReceiveTimestamp": "1545082650649" }, "messageAttributes": {}, "md5OfBody": "e4e68fb7bd0e697a0ae8f1bb342846b3", "eventSource": "aws:sqs", "eventSourceARN": "arn:aws:sqs:us-east-2:123456789012:my-queue", "awsRegion": "us-east-2" } ] }

By default, Lambda polls up to 10 messages in your queue at once and sends that batch to your function. To avoid invoking the function with a small number of records, you can tell the event source to buffer records for up to 5 minutes by configuring a batch window. Before invoking the function, Lambda continues to poll messages from the SQS standard queue until the batch window expires, the invocation payload size quota is reached, or the configured maximum batch size is reached.


If you're using a batch window and your SQS queue contains very low traffic, Lambda might wait for up to 20 seconds before invoking your function. This is true even if you set a batch window lower than 20 seconds.

Example FIFO queue message event

For FIFO queues, records contain additional attributes that are related to deduplication and sequencing.

Example Amazon SQS message event (FIFO queue)
{ "Records": [ { "messageId": "11d6ee51-4cc7-4302-9e22-7cd8afdaadf5", "receiptHandle": "AQEBBX8nesZEXmkhsmZeyIE8iQAMig7qw...", "body": "Test message.", "attributes": { "ApproximateReceiveCount": "1", "SentTimestamp": "1573251510774", "SequenceNumber": "18849496460467696128", "MessageGroupId": "1", "SenderId": "AIDAIO23YVJENQZJOL4VO", "MessageDeduplicationId": "1", "ApproximateFirstReceiveTimestamp": "1573251510774" }, "messageAttributes": {}, "md5OfBody": "e4e68fb7bd0e697a0ae8f1bb342846b3", "eventSource": "aws:sqs", "eventSourceARN": "arn:aws:sqs:us-east-2:123456789012:fifo.fifo", "awsRegion": "us-east-2" } ] }

Configuring a queue to use with Lambda

Create an SQS queue to serve as an event source for your Lambda function. Then configure the queue to allow time for your Lambda function to process each batch of events—and for Lambda to retry in response to throttling errors as it scales up.

To allow your function time to process each batch of records, set the source queue's visibility timeout to at least six times the timeout that you configure on your function. The extra time allows for Lambda to retry if your function is throttled while processing a previous batch.

If your function fails to process a message multiple times, Amazon SQS can send it to a dead-letter queue. If your function returns an error, all items in the batch return to the queue. After the visibility timeout occurs, Lambda receives the message again. To send messages to a second queue after a number of receives, configure a dead-letter queue on your source queue.


Make sure that you configure the dead-letter queue on the source queue, not on the Lambda function. The dead-letter queue that you configure on a function is used for the function's asynchronous invocation queue, not for event source queues.

If your function returns an error, or can't be invoked because it's at maximum concurrency, processing might succeed with additional attempts. To give messages a better chance to be processed before sending them to the dead-letter queue, set the maxReceiveCount on the source queue's redrive policy to at least 5.

Execution role permissions

Lambda needs the following permissions to manage messages in your Amazon SQS queue. Add them to your function's execution role.

Configuring a queue as an event source

Create an event source mapping to tell Lambda to send items from your queue to a Lambda function. You can create multiple event source mappings to process items from multiple queues with a single function. When Lambda invokes the target function, the event can contain multiple items, up to a configurable maximum batch size.

To configure your function to read from Amazon SQS in the Lambda console, create an SQS trigger.

To create a trigger
  1. Open the Functions page of the Lambda console.

  2. Choose the name of a function.

  3. Under Function overview, choose Add trigger.

  4. Choose the SQS trigger type.

  5. Configure the required options, and then choose Add.

Lambda supports the following options for Amazon SQS event sources:

SQS queue

The Amazon SQS queue to read records from.

Enable trigger

The status of the event source mapping. Enable trigger is selected by default.

Batch size

The number of records to send to the function in each batch. For a standard queue, this can be up to 10,000 records. For a FIFO queue, the maximum is 10. For a batch size over 10, you must also set the batch window (MaximumBatchingWindowInSeconds) to at least 1 second.

Configure your function timeout to allow enough time to process an entire batch of items. If items take a long time to process, choose a smaller batch size. A large batch size can improve efficiency for workloads that are very fast or have a lot of overhead. If you configure reserved concurrency on your function, set a minimum of five concurrent executions to reduce the chance of throttling errors when Lambda invokes your function.

Lambda passes all of the records in the batch to the function in a single call, as long as the total size of the events doesn't exceed the invocation payload size quota for synchronous invocation (6 MB). Both Lambda and Amazon SQS generate metadata for each record. This additional metadata is counted towards the total payload size and can cause the total number of records sent in a batch to be lower than your configured batch size. The metadata fields that Amazon SQS sends can be variable in length. For more information about the Amazon SQS metadata fields, see the ReceiveMessage API operation documentation in the Amazon Simple Queue Service API Reference.

Batch window

The maximum amount of time to gather records before invoking the function, in seconds. This applies only to standard queues.

If you're using a batch window greater than 0 seconds, you must account for the increased processing time in your queue's visibility timeout. We recommend setting your queue's visibility timeout to six times your function timeout, plus the value of MaximumBatchingWindowInSeconds. This allows time for your Lambda function to process each batch of events and to retry in the event of a throttling error.


If your batch window is greater than 0, and (batch window) + (function timeout) > (queue visibility timeout), then your effective queue visibility timeout is (batch window) + (function timeout) + 30s.

When messages become available, Lambda starts processing messages in batches. Lambda starts processing five batches at a time with five concurrent invocations of your function. If messages are still available, Lambda adds up to 60 more instances of your function a minute, up to a maximum of 1,000 function instances. To learn more about function scaling and concurrency, see Lambda function scaling.

To process more messages, you can optimize your Lambda function for higher throughput. See Understanding how AWS Lambda scales with Amazon SQS standard queues.

Maximum concurrency

The maximum number of concurrent functions that the event source can invoke. For more information, see Configuring maximum concurrency for Amazon SQS event sources.

Filter criteria

Add filter criteria to control which events Lambda sends to your function for processing. For more information, see Properly filtering Amazon SQS messages.

Scaling and processing

For standard queues, Lambda uses long polling to poll a queue until it becomes active. When messages are available, Lambda reads up to five batches and sends them to your function. If messages are still available, Lambda increases the number of processes that are reading batches by up to 60 more instances per minute. The maximum number of batches that an event source mapping can process simultaneously is 1,000.

For FIFO queues, Lambda sends messages to your function in the order that it receives them. When you send a message to a FIFO queue, you specify a message group ID. Amazon SQS ensures that messages in the same group are delivered to Lambda in order. Lambda sorts the messages into groups and sends only one batch at a time for a group. If your function returns an error, the function attempts all retries on the affected messages before Lambda receives additional messages from the same group.

Your function can scale in concurrency to the number of active message groups. For more information, see SQS FIFO as an event source on the AWS Compute Blog.

Configuring maximum concurrency for Amazon SQS event sources

The maximum concurrency setting limits the number of concurrent instances of the function that an Amazon SQS event source can invoke. Maximum concurrency is an event source-level setting. If you have multiple Amazon SQS event sources mapped to one function, each event source can have a separate maximum concurrency setting. You can use maximum concurrency to prevent one queue from using all of the function's reserved concurrency or the rest of the account's concurrency quota. You can use maximum concurrency and reserved concurrency together or independently.


You can't set maximum concurrency higher than the function's reserved concurrency. After configuring maximum concurrency, make sure that you don't reduce the function's reserved concurrency to less than the total maximum concurrency for all Amazon SQS event sources on the function. Otherwise, Lambda might throttle your messages. For FIFO queues, maximum concurrency is capped by the number of message groups.

There is no charge for configuring maximum concurrency on an Amazon SQS event source.

You can configure maximum concurrency on new and existing Amazon SQS event source mappings.

Configure maximum concurrency using the Lambda console
  1. Open the Functions page of the Lambda console.

  2. Choose the name of a function.

  3. Under Function overview, choose SQS. This opens the Configuration tab.

  4. Select the Amazon SQS trigger and choose Edit.

  5. For Maximum concurrency, enter a number between 2 and 1,000. To turn off maximum concurrency, leave the box empty.

  6. Choose Save.

Configure maximum concurrency using the AWS Command Line Interface (AWS CLI)

Use the update-event-source-mapping command with the --scaling-config option. Example:

aws lambda update-event-source-mapping \ --uuid "a1b2c3d4-5678-90ab-cdef-11111EXAMPLE" \ --scaling-config '{"MaximumConcurrency":5}'

To turn off maximum concurrency, enter an empty value for --scaling-config:

aws lambda update-event-source-mapping \ --uuid "a1b2c3d4-5678-90ab-cdef-11111EXAMPLE" \ --scaling-config "{}"
Configure maximum concurrency using the Lambda API

Use the CreateEventSourceMapping or UpdateEventSourceMapping action with a ScalingConfig object.

Event source mapping APIs

To manage an event source with the AWS Command Line Interface (AWS CLI) or an AWS SDK, you can use the following API operations:

The following example uses the AWS CLI to map a function named my-function to an Amazon SQS queue that is specified by its Amazon Resource Name (ARN), with a batch size of 5 and a batch window of 60 seconds.

aws lambda create-event-source-mapping --function-name my-function --batch-size 5 \ --maximum-batching-window-in-seconds 60 \ --event-source-arn arn:aws:sqs:us-east-2:123456789012:my-queue

You should see the following output:

{ "UUID": "2b733gdc-8ac3-cdf5-af3a-1827b3b11284", "BatchSize": 5, "MaximumBatchingWindowInSeconds": 60, "EventSourceArn": "arn:aws:sqs:us-east-2:123456789012:my-queue", "FunctionArn": "arn:aws:lambda:us-east-2:123456789012:function:my-function", "LastModified": 1541139209.351, "State": "Creating", "StateTransitionReason": "USER_INITIATED" }

Backoff strategy for failed invocations

When an invocation fails, Lambda attempts to retry the invocation while implementing a backoff strategy. The backoff strategy differs slightly depending on whether Lambda encountered the failure due to an error in your function code, or due to throttling.

  • If your function code caused the error, Lambda gradually backs off retries by reducing the amount of concurrency allocated to your Amazon SQS event source mapping. If invocations continue to fail, Lambda eventually drops the message without retrying.

  • If the invocation fails due to throttling, Lambda gradually backs off retries by reducing the amount of concurrency allocated to your Amazon SQS event source mapping. Lambda continues to retry the message until the message's timestamp exceeds your queue's visibility timeout, at which point Lambda drops the message.

Implementing partial batch responses

When your Lambda function encounters an error while processing a batch, all messages in that batch become visible in the queue again by default, including messages that Lambda processed successfully. As a result, your function can end up processing the same message several times.

To avoid reprocessing successfully processed messages in a failed batch, you can configure your event source mapping to make only the failed messages visible again. This is called a partial batch response. To turn on partial batch responses, specify ReportBatchItemFailures for the FunctionResponseTypes action when configuring your event source mapping. This lets your function return a partial success, which can help reduce the number of unnecessary retries on records.

When ReportBatchItemFailures is activated, Lambda doesn't scale down message polling when function invocations fail. If you expect some messages to fail—and you don't want those failures to impact the message processing rate—use ReportBatchItemFailures.


Keep the following in mind when using partial batch responses:

  • If your function throws an exception, the entire batch is considered a complete failure.

  • If you're using this feature with a FIFO queue, your function should stop processing messages after the first failure and return all failed and unprocessed messages in batchItemFailures. This helps preserve the ordering of messages in your queue.

To activate partial batch reporting
  1. Review the Best practices for implementing partial batch responses.

  2. Run the following command to activate ReportBatchItemFailures for your function. To retrieve your event source mapping's UUID, run the list-event-source-mappings AWS CLI command.

    aws lambda update-event-source-mapping \ --uuid "a1b2c3d4-5678-90ab-cdef-11111EXAMPLE" \ --function-response-types "ReportBatchItemFailures"
  3. Update your function code to catch all exceptions and return failed messages in a batchItemFailures JSON response. The batchItemFailures response must include a list of message IDs, as itemIdentifier JSON values.

    For example, suppose you have a batch of five messages, with message IDs id1, id2, id3, id4, and id5. Your function successfully processes id1, id3, and id5. To make messages id2 and id4 visible again in your queue, your function should return the following response:

    { "batchItemFailures": [ { "itemIdentifier": "id2" }, { "itemIdentifier": "id4" } ] }

    Here's an example of function code that returns the list of failed message IDs in the batch:

    Example – Python function code for batchItemFailures
    import json def lambda_handler(event, context): if event: batch_item_failures = [] sqs_batch_response = {} for record in event["Records"]: try: # process message except Exception as e: batch_item_failures.append({"itemIdentifier": record['messageId']}) sqs_batch_response["batchItemFailures"] = batch_item_failures return sqs_batch_response
    Example – Java function code for batchItemFailures
    import; import; import; import; import java.util.ArrayList; import java.util.List; public class ProcessSQSMessageBatch implements RequestHandler<SQSEvent, SQSBatchResponse> { @Override public SQSBatchResponse handleRequest(SQSEvent sqsEvent, Context context) { List<SQSBatchResponse.BatchItemFailure> batchItemFailures = new ArrayList<SQSBatchResponse.BatchItemFailure>(); String messageId = ""; for (SQSEvent.SQSMessage message : sqsEvent.getRecords()) { try { //process your message messageId = message.getMessageId(); } catch (Exception e) { //Add failed message identifier to the batchItemFailures list batchItemFailures.add(new SQSBatchResponse.BatchItemFailure(messageId)); } } return new SQSBatchResponse(batchItemFailures); } }

If the failed events do not return to the queue, see How do I troubleshoot Lambda function SQS ReportBatchItemFailures? in the AWS Knowledge Center.

Success and failure conditions

Lambda treats a batch as a complete success if your function returns any of the following:

  • An empty batchItemFailures list

  • A null batchItemFailures list

  • An empty EventResponse

  • A null EventResponse

Lambda treats a batch as a complete failure if your function returns any of the following:

  • An invalid JSON response

  • An empty string itemIdentifier

  • A null itemIdentifier

  • An itemIdentifier with a bad key name

  • An itemIdentifier value with a message ID that doesn't exist

CloudWatch metrics

To determine whether your function is correctly reporting batch item failures, you can monitor the NumberOfMessagesDeleted and ApproximateAgeOfOldestMessage Amazon SQS metrics in Amazon CloudWatch.

  • NumberOfMessagesDeleted tracks the number of messages removed from your queue. If this drops to 0, this is a sign that your function response is not correctly returning failed messages.

  • ApproximateAgeOfOldestMessage tracks how long the oldest message has stayed in your queue. A sharp increase in this metric can indicate that your function is not correctly returning failed messages.

Amazon SQS configuration parameters

All Lambda event source types share the same CreateEventSourceMapping and UpdateEventSourceMapping API operations. However, only some of the parameters apply to Amazon SQS.

Event source parameters that apply to Amazon SQS
Parameter Required Default Notes




For standard queues, the maximum is 10,000. For FIFO queues, the maximum is 10.






The ARN of the data stream or a stream consumer





Lambda event filtering



To let your function report specific failures in a batch, include the value ReportBatchItemFailures in FunctionResponseTypes. For more information, see Implementing partial batch responses.






Configuring maximum concurrency for Amazon SQS event sources