Configuring Lambda

Environment Variables

• Key-Value pairs in string form, available to lamdba code.

• Lambda also adds its own system environment variables.

• Can be used to store secret values (encrypted using KMS).

• Secrets can also be encrypted using Lambda secret service or CMK (Customer Master Key).

Logging & Monitoring

• If Lambda has execution role with an IAM policy that has write permission to CloudWatch, then all logs will be avaiable to CloudWatch Logs.

• Metrics are also displayed in AWS CloudWatch Metrics.

• Metrics such as success-rate, error count, throttles, async delivery failures, invocation count etc.

• Lambda Tracing can be enabled using X-Ray tracing (Active Tracing).

  • Once X-Ray tracing is enabled, Lambda will have X-Ray daemon running.

  • Once enabled, X-Ray SDK can be used.

  • Following environment variables should be configured in Lambda to communicate with X-Ray.

    Variable Name	Description
    _X_AMZN_TRACE_ID	Contains tracing header
    AWS_XRAY_CONTENT_MISSING	By default, LOG_ERROR
    AWS_XRAY_DAEMON_ADDRESS	X-Ray Daemon IP_ADDRESS:PORT

Lambda Function Configuration

• RAM can be increased from 128 MB to 10 GB, in 1 MB increments.

• The more RAM you add, the more VCPU credits get added.

• At 1792 MB, a function has equivalent of one full vCPU.

• After 1792 MB, you get more than one vCPU, so to benefit from it use multi threading.

• So, for CPU bound processing in lambda, make sure to increase the RAM, as there is no explicit setting to select number of vCPUS.

• Lambda by default will timeout by 3 seconds, but this can be increased upto 15 minutes.

Lambda concurrency executions

• Concurrency limit of upto 1000 concurrent executions.

• Reserved concurrency can be set to limit the concurrency at function level.

• It fucntion is invoked above the given concurrency limit, then it will trigger a Throttle.

  • For synchronous invocation, on encountering this limit lambda will throw 429 ThrottleError.

  • For asynchronous invocation, this will retry automatically and event will go to DLQ.

• Higher than 1000 concurrent executions can be achieved by connecting with AWS support team.

Concurrency Issues

• Limit issue

  • Concurrency Limit applies to all the functions in an account.

• Asynchronous Invocations

  • If functions doesnt have enough concurrency available to process all the events, additional requests are throttled.

  • For throttling errors, Lambda returns the event to the queue and attempt to run the function again for upto 6 hours.

  • The retry interval increases the exponentially from 1 second after first attempt to upto maximum of 5 minutes.

• Cold Start & Provisioned Concurrency

  • On first invocation of a lambda function, code is loaded and all code outside the lambda handler has to be run i.e., all the initialization code.

  • If initialization is large, then the process takes time. As a result, the first request served by new instances has higher latency than the rest.

  • To solve this cold start problem, one can use Provisioned Concurrency.

    • This allocates concurrency even before the function is invoked i.e, maintain a warm pool of execution context.

    • So, cold start never happens and all invocations have lower latency.

    • Application auto scaling can manage the concurrency (schedule or target utilization).

    • Will incur additional charges for this setup.

Lambda Function dependencies

• External dependencies should be packages along with code and zip it together.

• Once zip is created, upload it to Lambda, if less than 50 MB, else upload to S3 first and refer it from there.

• AWS SDK comes by default with every lamdba function.

References

• Provisioned and Reserved Concurrency