Configuring scaling behavior for SQS event source mappings - AWS Lambda
Maximum concurrency

Configuring scaling behavior for SQS event source mappings

For standard queues, Lambda uses long polling to poll a queue until it becomes active. When messages are available, Lambda starts processing five batches at a time with five concurrent invocations of your function. If messages are still available, Lambda increases the number of processes that are reading batches by up to 300 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. When Lambda reads your messages into batches, each batch may contain messages from more than one message group, but the order of the messages is maintained. If your function returns an error, the function attempts all retries on the affected messages before Lambda receives additional messages from the same group.

Configuring maximum concurrency for Amazon SQS event sources

You can use the maximum concurrency setting to control scaling behavior for your 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. There is no charge for configuring maximum concurrency on an Amazon SQS event source.

Importantly, maximum concurrency and reserved concurrency are two independent settings. Don't set maximum concurrency higher than the function's reserved concurrency. If you configure maximum concurrency, make sure that your function's reserved concurrency is greater than or equal to the total maximum concurrency for all Amazon SQS event sources on the function. Otherwise, Lambda may throttle your messages.

If maximum concurrency is not set, Lambda can scale your Amazon SQS event source up to your account's total concurrency quota, which is 1,000 by default.

Note

For FIFO queues, concurrent invocations are capped either by the number of message group IDs (messageGroupId) or the maximum concurrency setting—whichever is lower. For example, if you have six message group IDs and maximum concurrency is set to 10, your function can have a maximum of six concurrent invocations.

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.