resource/aws_lambda_function: Setting reserved_concurrent_executions to 0 will now disable Lambda Function invocations, causing downtime for the Lambda Function. Previously reserved_concurrent_executions accepted 0 and below for unreserved concurrency, which means it was not previously possible to disable invocations. The argument now differentiates between a new value for unreserved concurrency (-1) and disabling Lambda invocations (0). If previously configuring this value to 0 for unreserved concurrency, update the configured value to -1 or the resource will disable Lambda Function invocations on update. If previously unconfigured, the argument does not require any changes. See the Lambda User Guide for more information about concurrency.
raymondbutcher
commented
5 years ago
https://github.com/terraform-providers/terraform-provider-aws/blob/master/CHANGELOG.md#200-february-27-2019