aws_lambda_event_source_mapping: incorrectly setting values for optional resource parameters that weren't explicitly specified

[dlenski]

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Terraform CLI and Terraform AWS Provider Version

Terraform v0.12.29

* provider.aws: version = "~> 2.70"
* provider.null: version = "~> 2.1"
* provider.template: version = "~> 2.1"

Affected Resource(s)

• aws_lambda_event_source_mapping

I attempted to modify this existing aws_lambda_event_source_mapping resource:

resource "aws_lambda_event_source_mapping" "event_source_mapping_name" {
  batch_size             = 1000
  event_source_arn       = var.dynamo_stream_arn
  enabled                = true
  function_name          = aws_lambda_function.lambda_n.arn
  starting_position      = "TRIM_HORIZON"
}

Originally-intended changes (The parallelization factor feature for AWS lambda stream processing was announced in November 2019 and added to Terraform in 2d5b2cd#diff-943f35dca31585fb17f97dbca05290db.)

 resource "aws_lambda_event_source_mapping" "event_source_mapping_name" {
   batch_size             = 1000
+  parallelization_factor = 10
   event_source_arn       = var.dynamo_stream_arn
   enabled                = true
   function_name          = aws_lambda_function.lambda_n.arn
   starting_position      = "TRIM_HORIZON"
 }

Execution of these changes fails:

Error updating Lambda event source mapping: InvalidParameter: 1 validation error(s) found.
- minimum field value of 60, UpdateEventSourceMappingInput.MaximumRecordAgeInSeconds.

terraform plan shows why:

   # aws_lambda_event_source_mapping.event_source_mapping_name will be updated in-place
   ~ resource "aws_lambda_event_source_mapping" "event_source_mapping_name" {
         batch_size                         = 1000
         bisect_batch_on_function_error     = false
         enabled                            = true
         event_source_arn                   = "arn:aws:dynamodb:..."
         function_arn                       = "arn:aws:lambda:..."
         function_name                      = "arn:aws:lambda:..."
         id                                 = "deadbeef-dead-beef-f00f-deadbeeff00f"
         last_modified                      = "2020-08-06T05:49:00Z"
         last_processing_result             = "OK"
         maximum_batching_window_in_seconds = 0        # BAD!
         maximum_record_age_in_seconds      = 0        # BAD!
         maximum_retry_attempts             = 0        # BAD!
       ~ parallelization_factor             = 0 -> 10
         starting_position                  = "TRIM_HORIZON"
         state                              = "Enabled"
         state_transition_reason            = "User action"
         uuid                               = "deadbeef-dead-beef-f00f-deadbeeff00f"
     }

There are three other new parameters, marked with # BAD! above, which are apparently being set to a value of 0 even though:

• These parameters are all optional
• 0 is not even a legal value for maximum_record_age_in_seconds or maximum_retry_attempts

https://github.com/terraform-providers/terraform-provider-aws/blob/1c28287a3de773d41e20c174591f0fd355c59e1b/aws/resource_aws_lambda_event_source_mapping.go#L99-L120

Terraform Configuration Files

See relevant excerpt above.

Debug Output

See relevant excerpt above.

Panic Output

N/A

Expected Behavior

• Terraform should have not attempted to set the optional parameters of this resource, since no explicit value was indicated for them.

Actual Behavior

• Terraform attempted to set the value of 3 not-explicitly-included optional, numeric parameters to a value of 0 (which is neither a default value, nor even a valid value, for some of them)

• My hypothesis is that there is a faulty internal model for the state of an optional parameter that has never been set previously.

• In order to work around this, I had to explicitly set these parameters to their default values:

 resource "aws_lambda_event_source_mapping" "event_source_mapping_name" {
   batch_size             = 1000
+  parallelization_factor = 10
   event_source_arn       = var.dynamo_stream_arn
   enabled                = true
   function_name          = aws_lambda_function.lambda_n.arn
   starting_position      = "TRIM_HORIZON"

+  # Workaround for apparent Terraform issue?
+  # Default values of these parameters seem to be: https://github.com/awsdocs/aws-cloudformation-user-guide/pull/767
+  maximum_batching_window_in_seconds = 0
+  maximum_record_age_in_seconds      = 604800
+  maximum_retry_attempts             = 10000
 }

Steps to Reproduce

1. terraform apply

Important Factoids

N/A

References

• PR to add documentation on default values/semantics of AWS::Lambda::EventSourceMapping optional parameters: Document default values for optional parameters of AWS Lambda EventSourceMapping awsdocs/aws-cloudformation-user-guide#767

[danieladams456]

I'm not sure if this is related or not, but if I set batch_size and then remove that parameter or set it to null, I get the following error. I would expect it to go back to the default.

  # aws_lambda_event_source_mapping.event_source will be updated in-place
  ~ resource "aws_lambda_event_source_mapping" "event_source" {
      - batch_size                         = 5 -> null
        id                                 = "23c57369-45c0-492b-80fa-82964730f9e1"
        # (13 unchanged attributes hidden)
    }

Error: Error updating Lambda event source mapping: InvalidParameter: 1 validation error(s) found.
- minimum field value of 1, UpdateEventSourceMappingInput.BatchSize.

[dlenski]

@danieladams456, definitely seems like it could be related. In both cases, a not-present optional parameter is getting set to a value that isn't legal for it.

[HongChenTW]

Hi @dlenski, seems that your PR was overwritten by AWS docs auto-gen mechanism...

awsdocs/aws-cloudformation-user-guide@b2a0d98

This has been released in version 3.38.0 of the Terraform AWS provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue following the template for triage. Thanks!

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