AWS Lambda Provisioned Concurrency is a feature that keeps a specified number of Lambda function instances initialized and ready to respond to invocations. This addresses the cold start latency issue that occurs when Lambda needs to initialize new execution environments.
When a Lambda function is …AWS Lambda Provisioned Concurrency is a feature that keeps a specified number of Lambda function instances initialized and ready to respond to invocations. This addresses the cold start latency issue that occurs when Lambda needs to initialize new execution environments.
When a Lambda function is invoked after being idle, AWS must create a new execution environment, download the code, initialize the runtime, and run initialization code. This process, known as a cold start, can add significant latency ranging from milliseconds to several seconds depending on the runtime and code complexity.
With Provisioned Concurrency, you pre-warm a defined number of execution environments. These instances remain initialized and ready, ensuring consistent low-latency responses for your applications. This is particularly valuable for latency-sensitive workloads like APIs, real-time processing, or interactive applications.
Key aspects of Provisioned Concurrency include:
1. Configuration: You specify the number of concurrent executions to keep warm on a function version or alias. You cannot configure it on the $LATEST version.
2. Scaling: Provisioned Concurrency handles requests up to the configured level. If traffic exceeds this, Lambda uses standard on-demand scaling, which may include cold starts.
3. Cost: You pay for the provisioned capacity whether used or not, plus standard execution charges when functions run. This makes it more expensive than on-demand Lambda.
4. Application Auto Scaling: You can configure automatic scaling of Provisioned Concurrency based on schedules or utilization metrics to optimize costs.
5. Initialization: All initialization code runs during provisioning, so database connections and SDK clients are ready before handling requests.
Provisioned Concurrency is ideal for production workloads requiring predictable performance. For development or variable traffic patterns, on-demand concurrency remains cost-effective. Combining both approaches with Application Auto Scaling provides optimal balance between performance and cost efficiency.
Lambda Provisioned Concurrency - Complete Guide
Why Lambda Provisioned Concurrency is Important
Lambda Provisioned Concurrency addresses one of the most significant challenges with serverless computing: cold starts. When a Lambda function hasn't been invoked recently, AWS needs to initialize a new execution environment, which causes latency spikes. For applications requiring consistent, low-latency responses (like APIs, real-time processing, or customer-facing applications), this unpredictable latency can be unacceptable.
What is Lambda Provisioned Concurrency?
Provisioned Concurrency is a Lambda feature that keeps a specified number of function instances initialized and ready to respond at all times. These pre-warmed instances eliminate cold start latency by ensuring your function can handle requests with consistent performance.
Key characteristics: - Pre-initializes execution environments before invocations - Maintains a pool of ready-to-execute instances - Provides predictable, double-digit millisecond latency - Can be configured on a published version or alias (not $LATEST) - Incurs charges for the provisioned capacity whether used or not
How Provisioned Concurrency Works
1. Configuration: You specify the number of concurrent executions to keep initialized for a specific function version or alias
2. Initialization: AWS pre-creates the specified number of execution environments, running your initialization code
3. Request Handling: Incoming requests are routed to pre-warmed instances, providing consistent latency
4. Scaling: If requests exceed provisioned capacity, Lambda uses standard on-demand instances (which may experience cold starts)
5. Auto Scaling: You can use Application Auto Scaling to adjust provisioned concurrency based on schedules or utilization metrics
Provisioned Concurrency vs On-Demand Concurrency
On-Demand: Default behavior where Lambda creates instances as needed, potential cold starts, pay only for actual execution time
Provisioned: Pre-initialized instances, consistent latency, pay for provisioned capacity plus execution time
Use Cases for Provisioned Concurrency
- Interactive APIs requiring consistent response times - Synchronous invocations where latency matters - Scheduled traffic spikes (product launches, marketing campaigns) - Functions with lengthy initialization code - Financial or healthcare applications with strict SLAs
Configuring Provisioned Concurrency
Provisioned Concurrency can only be set on: - Published versions (e.g., version 1, version 2) - Aliases pointing to specific versions - Cannot be configured on $LATEST
Provisioned Concurrency has two cost components: 1. Provisioned Concurrency charge: For keeping instances initialized (per GB-hour) 2. Request and duration charges: Standard Lambda charges when functions execute
This makes it more expensive than on-demand for infrequent invocations but valuable when consistent performance is required.
Exam Tips: Answering Questions on Lambda Provisioned Concurrency
Scenario Recognition: - Look for keywords like cold start, latency spikes, consistent performance, predictable response times, or initialization delays - Questions mentioning APIs with strict latency requirements often point to Provisioned Concurrency
Key Facts to Remember: - Provisioned Concurrency eliminates cold starts for the configured capacity - Must be configured on a published version or alias, never on $LATEST - Use Application Auto Scaling to dynamically adjust provisioned capacity - Requests exceeding provisioned capacity fall back to on-demand instances
Common Exam Distractors: - Reserved Concurrency (limits maximum concurrency, does NOT reduce cold starts) - Increasing memory allocation (improves performance but does not eliminate cold starts) - VPC configuration changes (may affect networking but not cold start behavior)
Remember the Trade-offs: - Provisioned Concurrency costs more but provides consistent latency - Best for predictable, high-traffic workloads or strict latency requirements - Not cost-effective for sporadic or unpredictable traffic patterns
Integration Points: - Works with CloudWatch alarms for monitoring utilization - Integrates with Application Auto Scaling for scheduled or metric-based scaling - Can be deployed through SAM, CloudFormation, or CDK