Get lambda Full account concurrency and Unreserved account concurrency

[pendyalal]

Is your feature request related to a problem? Please describe.
we are unable to get lambda account level concurrency limits.

Describe the solution you'd like
We want to get Lambda Full account and Unreserved account concurrency limits per region in an account. If the unreserved concurrency falls below a certain threshold, then set the concurrency to a specific value for each lambda function that has more than 100 concurrent executions in 5 minutes. This is to ensure all Lambda functions get fair reserved capacity.

https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/lambda.html#Lambda.Client.get_account_settings

[kapilt]

if your concurrency is exhausted, using a lambda to check it and respond after the fact isn't a good approach. why not just set an upper bound per function? and tag exempt those with needs.

[pendyalal]

@kapilt ,That's true if the reserved concurrency is set on the lambda function.
There is a concurrency executions metric for each function. If the concurrency executions is more than 100 for 5 minutes and If the lambda function doesn't have a reserved concurrency set on lambda and if the unreserved account concurrency is more than 50% of full account concurrency then we want to set concurrency to 100 on the lambda.

[pendyalal]

@kapilt , Is there a way to get unreserved account concurrency and full account concurrency using custodian policy?

[kapilt]

we probably need to expose metric filter on the account to have this available, but you also want comparisons between the two metrics.. which relates to #5625