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AWS Lambda 0.21.18Last updated in version 0.21.16

Keep Warm Module

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This is a Lambda function you can use to invoke your other Lambda functions on a scheduled basis to keep those functions "warm." This is necessary for Lambda functions that require a low response time (e.g., if you're using Lambda API Gateway as a web service), as Lambda functions that have not been executed in a while will be shut down (that is, the underlying Docker container will be stopped), and the next time that function is executed, you will be faced with the overhead of starting the function again. This is known as a "cold start" and the overhead can be from a few hundred milliseconds all the way up to 15 seconds (the latter is mostly for cold start in a VPC). For more info on cold starts, see:

Concurrency​

An important idea to understand is that a cold start happens once for each concurrent execution of your function. If the same function is executed more than once at roughly the same time, then each of those executions will happen in a separate Docker container. If this is the first time executing that container in a long time, it will be subject to a cold start.

Therefore, if your Lambda functions may be executed concurrently, you will need to use the concurrency parameter in this module to tell it to execute your function concurrently and keep multiple containers warm at the same time. For example, if your Lambda function is idle most of the time, but periodically, traffic spikes and you need to support 5 simultaneous executions of it, you should set concurrency = 5 in the keep-warm module.

How often should you run this function?​

AWS is making rapid changes to Lambda, so it's hard to say exactly how long the underlying Docker containers will be kept around, but as of May, 2018, it seems that Lambda functions that are inactive for 10 - 15 minutes get shut down. Therefore, you should probably run the keep-warm function every 5-10 minutes, with the appropriate concurrency level for your functions.

Sample Usage​

main.tf

# ------------------------------------------------------------------------------------------------------
# DEPLOY GRUNTWORK'S KEEP-WARM MODULE
# ------------------------------------------------------------------------------------------------------

module "keep_warm" {

  source = "git::git@github.com:gruntwork-io/terraform-aws-lambda.git//modules/keep-warm?ref=v0.21.18"

  # ----------------------------------------------------------------------------------------------------
  # REQUIRED VARIABLES
  # ----------------------------------------------------------------------------------------------------

  # A map where the keys are the ARNs of Lambda functions to invoke (to keep
  # them warm) and the values are the event objects to send to those functions
  # when invoking them.
  function_to_event_map = <any>

  # The name for this Lambda function. Also used to namespace the other
  # resources created by this module.
  name = <string>

  # An expression that defines how often to invoke the functions in
  # var.function_to_event_map. For example, cron(0 20 * * ? *) or rate(5
  # minutes).
  schedule_expression = <string>

  # ----------------------------------------------------------------------------------------------------
  # OPTIONAL VARIABLES
  # ----------------------------------------------------------------------------------------------------

  # The ID (ARN, alias ARN, AWS ID) of a customer managed KMS Key to use for
  # encrypting log data.
  cloudwatch_log_group_kms_key_id = null

  # The number of days to retain log events in the log group. Refer to
  # https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/cloudwatch_log_group#retention_in_days
  # for all the valid values. When null, the log events are retained forever.
  cloudwatch_log_group_retention_in_days = null

  # Tags to apply on the CloudWatch Log Group, encoded as a map where the keys
  # are tag keys and values are tag values.
  cloudwatch_log_group_tags = null

  # How many concurrent requests to send to each Lambda function in
  # var.function_to_event_map. With Lambda, each concurrent requests to the same
  # function spins up a new container that must be kept warm, so you'll want to
  # set this number to roughly the expected concurrency you see in real-world
  # usage.
  concurrency = 1

  # When true, precreate the CloudWatch Log Group to use for log aggregation
  # from the lambda function execution. This is useful if you wish to customize
  # the CloudWatch Log Group with various settings such as retention periods and
  # KMS encryption. When false, AWS Lambda will automatically create a basic log
  # group to use.
  should_create_cloudwatch_log_group = true

  # When true, all IAM policies will be managed as dedicated policies rather
  # than inline policies attached to the IAM roles. Dedicated managed policies
  # are friendlier to automated policy checkers, which may scan a single
  # resource for findings. As such, it is important to avoid inline policies
  # when targeting compliance with various security standards.
  use_managed_iam_policies = true

}


Reference​

Required​

A map where the keys are the ARNs of Lambda functions to invoke (to keep them warm) and the values are the event objects to send to those functions when invoking them.

Any types represent complex values of variable type. For details, please consult `variables.tf` in the source repo.
Example
   default = {
     "arn:aws:lambda:us-east-1:123456789011:function:my-function-foo" = {}
  
     "arn:aws:lambda:us-east-1:123456789011:function:my-function-bar" = {
        foo  = "bar"
        blah = 12345
     }
   }

namestringrequired

The name for this Lambda function. Also used to namespace the other resources created by this module.

schedule_expressionstringrequired

An expression that defines how often to invoke the functions in function_to_event_map. For example, cron(0 20 * ? ) or rate(5 minutes).

Optional​

The ID (ARN, alias ARN, AWS ID) of a customer managed KMS Key to use for encrypting log data.

null

The number of days to retain log events in the log group. Refer to https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/cloudwatch_log_group#retention_in_days for all the valid values. When null, the log events are retained forever.

null
cloudwatch_log_group_tagsmap(string)optional

Tags to apply on the CloudWatch Log Group, encoded as a map where the keys are tag keys and values are tag values.

null
concurrencynumberoptional

How many concurrent requests to send to each Lambda function in function_to_event_map. With Lambda, each concurrent requests to the same function spins up a new container that must be kept warm, so you'll want to set this number to roughly the expected concurrency you see in real-world usage.

1

When true, precreate the CloudWatch Log Group to use for log aggregation from the lambda function execution. This is useful if you wish to customize the CloudWatch Log Group with various settings such as retention periods and KMS encryption. When false, AWS Lambda will automatically create a basic log group to use.

true

When true, all IAM policies will be managed as dedicated policies rather than inline policies attached to the IAM roles. Dedicated managed policies are friendlier to automated policy checkers, which may scan a single resource for findings. As such, it is important to avoid inline policies when targeting compliance with various security standards.

true