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).

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

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.

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.

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.

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.

Last updated 5 months ago