This post is written by Tarun Rai Madan, Principal Product Manager, Serverless Compute and Rajesh Kumar Pandey, Principal Software Engineer, Serverless Compute

AWS is announcing the general availability of Provisioned Mode for AWS Lambda Event Source Mappings (ESMs) that subscribe to Apache Kafka event sources including Amazon MSK and self-managed Kafka. Provisioned Mode allows you to optimize the throughput of your Kafka ESM by provisioning event polling resources that remain ready to handle sudden spikes in traffic. Controlling the throughput of your ESM helps you build highly responsive and scalable event-driven Kafka applications with stringent performance requirements.

Overview

When you build modern applications using Event-Driven Architectures (EDAs), your event producers publish events, which are then processed by event source connectors like an ESM, and routed to serverless compute consumers like Lambda functions. Apache Kafka is a popular open-source platform for building real-time streaming data applications using Lambda functions as consumers. AWS Lambda’s fully-managed MSK ESM or self-managed Kafka ESM reads events from Kafka as an event source, performs operations like filtering and batching, and invokes Lambda functions. Both ESMs offer built-in integrations with event sources, auto-scaling, and features like batching and filtering. When a Kafka ESM is created, Lambda ESM allocates one event poller to start polling for messages in a Kafka topic. The ESM then evaluates the message backlog – using the OffsetLag metric – for all partitions in the topic, and auto-scales event pollers to process messages efficiently.

Many real-time applications using Kafka are sensitive to sudden spikes in traffic, which could lead to noticeable delays in your end users’ experience. Previously, there were no controls to optimize the throughput for performance-sensitive workloads when using Kafka ESMs. This forced you to explore alternative solutions for workloads with strict performance requirements, which added architectural complexity. To harness the power of Lambda for such performance-sensitive applications, you need to be able to control your Kafka ESM’s throughput and ensure responsive auto-scaling behavior.

What’s new

Provisioned Mode for ESM is a feature that helps you control the throughput of your ESM, and achieve an enhanced performance profile for performance-sensitive applications, particularly ones that see sudden spikes in traffic. You can use Provisioned Mode for Kafka ESM with a range of Kafka or Kafka-compatible streaming data platform providers like Amazon MSK, Confluent, Redpanda, and self-managed Kafka. Key benefits include:

1. Controls to optimize throughput: You can now fine-tune the throughput of your ESM by configuring a minimum and maximum number of resources called “event pollers”. An event poller (or a “poller”) represents a compute resource that underpins an ESM in the Provisioned Mode, and allocates up to 5 MB/s throughput.
2. Responsive auto-scaling: With Provisioned Mode, your Kafka ESM detects the increase in OffsetLag metric for all partitions in your Kafka topic, and auto-scales event pollers in a responsive manner. During idle periods, your ESM automatically scales down to the minimum event pollers set by you.
3. Simplified networking experience and charges: Previously, you were required to configure AWS PrivateLink or NAT Gateway to enable Lambda to poll messages from Kafka clusters in your VPC and invoke Lambda functions. With Provisioned Mode, you are no longer required to configure PrivateLink or NAT Gateway. This approach reduces overhead and improves the developer experience, allowing you to focus on building applications rather than managing networking setup. Consequently, you are not charged for PrivateLink VPC endpoints when using Kafka as an event source with Lambda in the Provisioned Mode for ESM, which reduces your networking charges.

Activating Provisioned Mode for ESM

To activate Provisioned Mode for a new or existing Kafka ESM, you can configure the minimum event pollers, the maximum event pollers, or both for your ESM. The allowed values range from 1 to 200 for minimum event pollers, and from 1 to 2000 for maximum event pollers.

Note that you must configure at least one of minimum or maximum event pollers to activate Provisioned Mode. When you configure only the minimum number of event pollers (‘Min-only’), your ESM allocates this minimum quantity and can dynamically scale up to a maximum. This maximum is determined by the OffsetLag and is limited by either the number of partitions or the default maximum event pollers, whichever is lower. When you configure only the maximum number of event pollers (“Max-only”), your ESM starts with one minimum poller by default, and can scale up to the maximum event pollers or number of partitions, whichever is lower. When you configure both the minimum and maximum number of event pollers (“Min and Max”), your ESM can auto-scale between this range of minimum and maximum event pollers configured.

Activating using AWS CLI

You can activate Provisioned Mode for ESM during creation of a new ESM, or by updating an existing ESM. Specify the –provisioned-poller-config parameter.

aws lambda create-event-source-mapping \ --region <region-name> \ --function-name <function-name> \ --event-source-arn <event-source-arn> \ --provisioned-poller-config '{"MinimumPollers":<number>, "MaximumPollers":<number>}'

Activating using AWS Lambda Console

Select Configure provisioned mode to activate Provisioned Mode when creating a new ESM, or updating an existing one.

Figure 1: Activating Provisioned Mode for ESM in Console

Provisioned Mode for Kafka ESM in action

To see the performance profile with Provisioned Mode for Kafka ESM, deploy a Lambda function that subscribes to an Amazon MSK topic. Use the reference pattern on Serverless Land and see this blog post outlining steps to configure MSK ESM for a Lambda function. In this case, a producer writes 20 million messages, each with 1KB payload size to an MSK topic – distributed evenly across 100 partitions. Use a batch size of 100, with function duration at 100ms, and set the StartingPosition to TRIM_HORIZON to process from the beginning of the stream.

Note the baseline performance profile observed with the default On-Demand mode. Then analyze two configurations with the Provisioned Mode activated.

• Scenario 1 uses different configurations for minimum event pollers
• Scenario 2 uses the default minimum event pollers and lets Lambda manage the event pollers through autoscaling.

Baseline performance profile for Kafka ESM On-demand

With Provisioned Mode disabled, Lambda takes approximately 20 minutes to drain the backlog of 20 million messages. It takes 4 minutes to reach the maximum concurrent executions. Use this result as a baseline to compare against Provisioned Mode for ESM.

Figure 2: Baseline performance without Provisioned Mode for ESM

Scenario 1: Configuring minimum event pollers, and auto-scaling

To optimize the ESM throughput for this workload and reduce the time to drain the message backlog, configure the minimum event pollers. Select values of 10 and 100 for minimum event pollers, and observe the results.

Configuring 10 minimum event pollers

Lambda drains the backlog of 20 million messages in approximately 11 minutes with minimum pollers set to 10. This is 45% faster than the baseline without Provisioned Mode. It takes approximately 6 minutes to reach maximum concurrent executions.

Figure 3: Performance profile with minimum event pollers set to 10

Configuring 100 minimum event pollers

To further improve the processing performance, configure the minimum event pollers to 100. Lambda now takes 6 minutes to drain the backlog of 20 million messages, which is 70% faster than the baseline. It instantly reaches the maximum concurrent executions.

Figure 4: Performance profile with minimum event pollers set to 100

Scenario 2: Default minimum event pollers, and auto-scaling

In some cases, the workload may not be as performance-sensitive. With the same volume of 20M messages in your Kafka topic, activate Provisioned Mode for ESM. Start with the default minimum event pollers (set to 1) and let Lambda auto-scale the event pollers based on incoming traffic.

Lambda automatically scales up your event pollers to process the incoming messages, and scales them down as the backlog is cleared. With the default minimum and maximum event pollers, Lambda takes approximately 12 minutes to clear the backlog of 20 million messages, which is 40% faster than the baseline. Lambda takes 7 minutes to reach maximum concurrent executions.

Figure 5: Performance profile with minimum event pollers set to 1

The following table summarizes the performance improvement for the analyzed workload using Provisioned Mode for ESM.

ESM Mode	Time to drain message backlog	Percentage improvement
On-demand Mode	20 minutes	Baseline
Provisioned Mode: Scenario 1 (fine-tuned minimum event pollers)
Minimum event pollers = 10	11 minutes	45%
Minimum event pollers = 100	6 minutes	70%
Provisioned Mode: Scenario 2 (default minimum event pollers)
Minimum event pollers = 1	12 minutes	40%

Table: Performance profile for reference test case before and after activating Provisioned Mode for ESM

Observability and Pricing

You can observe the usage of event pollers by monitoring the ProvisionedPollers Amazon CloudWatch metric, which measures the number of event pollers that actively processed at least one event in the last 5-minute window.

Pricing is based on the provisioned minimum event pollers and the number of event pollers consumed during automatic scaling. Provisioned Mode introduces a billing unit called Event Poller Unit (EPU). Each EPU supports up to 20 MB/s of throughput for event polling. The number of event pollers allocated on an EPU depends on the throughput consumed by each event poller. You pay for the number of EPUs used and the duration they run for, measured in Event Poller Unit hours. For details, refer to AWS Lambda pricing.

Best practices and considerations

The optimal configuration of minimum and maximum event pollers for your Kafka Event Source Mapping (ESM) depends on your application’s performance requirements. Start with the default minimum event pollers to baseline the performance profile, and adjust event pollers based on observed message processing patterns and your application’s performance requirements. For workloads with spiky traffic and strict performance needs, increase the minimum event pollers to handle sudden surges. You can fine-tune the minimum required event pollers by evaluating your desired throughput, your observed throughput – which depends on factors like the ingested messages per second and average payload size, and using the throughput capacity of one event poller (up to 5 MB/s) as reference. Note that to maintain ordered processing within a partition, Lambda caps the maximum event pollers at the number of partitions in the topic.

Update your network settings to remove PrivateLink VPC endpoints and associated permissions for existing ESMs when you activate Provisioned Mode.

Conclusion

Provisioned Mode for Lambda ESM allows you to fine-tune the throughput for your Kafka ESMs by configuring a minimum and maximum number of event pollers. This provides a responsive auto-scaling behavior for Kafka applications that have stringent performance requirements and see unpredictable and spiky traffic. You can fine-tune your configured event pollers based on your requirements and monitor usage via CloudWatch metrics. Provisioned Mode also simplifies network configuration by removing the requirement to configure PrivateLink.

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