Functions that don't have reserved concurrency defined need to be able to scale when necessary. AWS insists that you leave 100 invocations for such functions.
you can use upto Unreserved account concurrency minus 100 when defining reserved concurrency for your functions.
You can reserve up to the Unreserved account concurrency value that is shown, minus 100 for functions that don't have reserved concurrency. To throttle a function, set the reserved concurrency to zero. This stops any events from being processed until you remove the limit.
Use GetAccountSettings to see your Regional concurrency limit. You can reserve concurrency for as many functions as you like, as long as you leave at least 100 simultaneous executions unreserved for functions that aren't configured with a per-function limit.
https://docs.aws.amazon.com/lambda/latest/dg/configuration-concurrency.html
Answer from shamanth Gowdra Shankaramurthy on Stack ExchangeTrend Micro
trendmicro.com › cloudoneconformity › knowledge-base › aws › Lambda › lambda-function-reserved-concurrency.html
Enable and Configure Reserved Concurrency | Trend Micro
November 17, 2023 - 06 On the Edit concurrency configuration page, select Reserve concurrency under Concurrency, and enter the amount of concurrency to reserve for the selected Lambda function. Choose Save to apply the configuration changes. 07 Repeat steps no. 4 – 6 for each Amazon Lambda function that you ...
AWS Lambda Reserved Concurrency
no, it is not possible. lambda instances don't know about each other. it has to be something about sqs visibility timeout, and some error in signaling the processing of messages. More on reddit.com
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December 27, 2024How does Lambda reserved concurrency interact with Cloudwatch Events?
When your reserved concurrency is hit for a function, Lambda will respond to the client calling it’s Invoke API with a 429 status code. What happens next depends on the event source and it’s retry behavior. See here: https://docs.aws.amazon.com/lambda/latest/dg/invocation-retries.html More on reddit.com
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February 9, 2021Having trouble with the difference between reserved and provisioned concurrency
Imagine you are going to rent 5 cars and they have 1000 cars and a delivery time of around 30 min Reserved concurrency means that even if 1000 people shows to rent a car, the rental will only be able to rent 995 because you reserved the other 5, however, you will have to wait the usual 30 minutes to get a car the moment you want it. A Provisioned concurrency of 1 means that in addition to have 5 cars reserved for yourself, the car rental hired someone to follow you around in one car like a creep all the time, so whenever you want to rent a car, you just hop in and skip the 30 minute wait time More on reddit.com
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November 14, 2020Lambda: Reserved Concurrency and SQS
I would create a dynamodb table with a lock the lambda acquires More on reddit.com
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November 25, 2022Videos
13:09
AWS Lambda Concurrency Explained - YouTube
05:34
learn about AWS lambda Concurrency | what is provision and reserved ...
43:13
AWS SQS and Lambda Reserved Concurrency - YouTube
02:33
AWS Lambda Concurrency Explained | Reserved vs Provisioned ...
17:51
How does AWS Lambda Concurrency Work? - YouTube
13:02
AWS Lambda Concurrency - Provisional & Reserved - YouTube
AWS re:Post
repost.aws › knowledge-center › lambda-reserved-concurrency
Troubleshoot Lambda reserved concurrency issues | AWS re:Post
October 26, 2022 - 4. Increase the reserved concurrency for your Lambda function to a concurrency value that keeps the function from being throttled. Change the setting using the Lambda console, or by calling the PutFunctionConcurrency API. 5. If you still can’t resolve the issue, open a case with AWS Support.
Reddit
reddit.com › r/aws › aws lambda reserved concurrency
r/aws on Reddit: AWS Lambda Reserved Concurrency
December 27, 2024 -
Hey! Maybe this is a dumb question, maybe a coincidence.
We have a lambda configured to use Reserved Concurrency = 5.
Sometimes this lambda takes more than a minute run and, when we trigger this lambda with more than 50 requests ( it is fired by sqs ), we notice that the lambda returns 5 by 5 and it ends its execution all 5 together.
For example, we have a bunch of requests which takes 5 seconds to process each, if we trigger our lambda with 40 requests if one take more than 30s, the lambda return 5 of the results together after 30 seconds, even if the others takes less than 2 or 3s.
Is this a common behavior for lambdas with reserved concurrency?
It sends 5 requests, waits until all 5 executes then send more 5? Or it send 5 requests, when one ends it sends another one to keep 5 itens running concurrently?
Top answer 1 of 3
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no, it is not possible. lambda instances don't know about each other. it has to be something about sqs visibility timeout, and some error in signaling the processing of messages.
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Reserved Concurrency is to take from the account max lambda concurrency and allocate it to that function (version). The default account limit is 1000 concurrent lambda executions. This means 995 are still available for this or other functions. It is not a limit, just an allocation. Using SQS, the Lambda service starts with 5 workers. Each worker will pull up to your batch size of messages. The lambda function will process the entire batch within the timeout. It is recommended you have your lambda execution timeout set long enough to process the entire batch of messages. If any message in the batch fails, the entire batch will fail. So plan for idempotency - and best practice is for lambda function to delete each completed message from SQS upon completion, they way they won’t be returned as a failed message if the batch fails. Lambda service will add and remove workers based upon the size of SQS, oldest message and error rates. You have no control over this, other than by setting a maximum currency on your lambda function. So, your visibility time out on SQS needs to be long enough that the queue doesn’t just redrive the messages. Your lambda function needs to have execution time long enough to process the entire batch. You can adjust the batch size.
Amazon Web Services
docs.aws.amazon.com › cli › latest › reference › lambda › put-function-concurrency.html
put-function-concurrency — AWS CLI 2.31.35 Command Reference
The following put-function-concurrency example configures 100 reserved concurrent executions for the my-function function. aws lambda put-function-concurrency \ --function-name my-function \ --reserved-concurrent-executions 100
Serverless Land
serverlessland.com › content › service › lambda › guides › aws-lambda-operator-guide › reserved-concurrency
AWS Lambda Operator Guide | Reserved concurrency
Your resource for learning serverless technology
Medium
medium.com › the-symphonium › aws-lambda-reserved-concurrency-f2c3a32b9f1d
AWS Lambda Reserved Concurrency. The most important new text box of… | by Mike Roberts | The Symphonium | Medium
December 13, 2017 - It makes sure there is always at least enough concurrency capability available in the account to run the number of instances requested. In the screenshot above I’ve specified that the reserved concurrency for my function is 20.
AWS re:Post
repost.aws › knowledge-center › lambda-provisioned-reserved-concurrency
List Lambda functions with concurrency | AWS re:Post
April 30, 2024 - The code iterates through each Lambda function. The function calls the get_function_concurrency method to retrieve details about the reserved or provisioned concurrency configuration for each function in the specified AWS Region.
LinkedIn
linkedin.com › pulse › simplifying-aws-lambda-understanding-reserved-vs-piñero-estrada-davme
Simplifying AWS Lambda. Understanding Reserved vs. Provisioned Concurrency
April 5, 2024 - Reserved Concurrency is like reserving a certain number of clerks exclusively for your store. No matter how busy the mall gets, you are guaranteed that number of clerks. In AWS Lambda terms, it means setting aside a specific number of execution ...
Amazon Web Services
docs.aws.amazon.com › cli › latest › reference › lambda › get-function-concurrency.html
get-function-concurrency — AWS CLI 2.31.28 Command Reference
The following get-function-concurrency example retrieves the reserved concurrency setting for the specified function. aws lambda get-function-concurrency \ --function-name my-function
Stack Overflow
stackoverflow.com › beta › discussions › 78231813 › difference-between-aws-lambda-reserved-and-unreserved-concurrency
Difference between AWS Lambda Reserved and Unreserved Concurrency - Stack Overflow
March 27, 2024 - Once the container is up, and the lambda is executed successfully, AWS keeps this container up to avoid cold start and waits for the next request from same function. From my experience this wait time is around 10 mins(not documented anywhere). 2. Now coming to Concurrency, the default limit is 1000(which can be increased upon requesting AWS).
Amazon Web Services
docs.aws.amazon.com › aws lambda › developer guide › invoking lambda with events from other aws services › using lambda with amazon sqs › configuring scaling behavior for sqs event source mappings
Configuring scaling behavior for SQS event source mappings - AWS Lambda
Importantly, maximum concurrency and reserved concurrency are two independent settings. Don't set maximum concurrency higher than the function's reserved concurrency. If you configure maximum concurrency, make sure that your function's reserved concurrency is greater than or equal to the total maximum concurrency for all Amazon SQS event sources on the function.
Substack
urielbitton.substack.com › p › using-reserved-vs-unreserved-concurrency
Using Reserved Vs Unreserved Concurrency in AWS Lambda
June 26, 2025 - When a function uses unreserved concurrency it can use up as much as it needs from the pool of total concurrency and starve other functions. Reserved concurrency on the other hand guarantees your function always has a set number of concurrency.
KodeKloud Notes
notes.kodekloud.com › docs › AWS-Lambda › Advanced-Topics › Reserved-and-Unreserved-Concurrency
Reserved and Unreserved Concurrency - KodeKloud Notes
Managing concurrency in AWS Lambda ensures that high-priority functions always have the capacity they need. By default, your account’s unreserved concurrency sets a soft limit on total parallel executions. For mission-critical workloads, you can allocate reserved concurrency to specific functions.
Amazon Web Services
docs.aws.amazon.com › aws lambda › developer guide › understanding lambda function scaling › monitoring concurrency
Monitoring concurrency - AWS Lambda
UnreservedConcurrentExecutions is the number of active concurrent invocations that are using unreserved concurrency. Allocated concurrency is the sum of the following two parts (substituting RC as "reserved concurrency" and PC as "provisioned concurrency"):
Lumigo
lumigo.io › guides › aws lambda performance optimization › aws lambda concurrency
AWS Lambda Concurrency - Lumigo
August 21, 2024 - Provisioned concurrency lets AWS Lambda prepare containers for functions in advance. This means you can invoke functions with a double digit millisecond latency, even if the function was not called previously. Important note: While reserved concurrency is offered at no additional cost (included in the cost of regular Lambda invocations), provisioned concurrency incurs extra costs.
Amazon Web Services
docs.aws.amazon.com › aws lambda › developer guide › understanding lambda function scaling › configuring reserved concurrency for a function
Configuring reserved concurrency for a function - AWS Lambda
In Lambda, concurrency is the number of in-flight requests that your function is currently handling. There are two types of concurrency controls available: Reserved concurrency – This sets both the maximum and minimum number of concurrent instances allocated to your function.
Amazon Web Services
docs.aws.amazon.com › aws lambda › developer guide › understanding lambda function scaling
Understanding Lambda function scaling - AWS Lambda
By default, Lambda provides your account with a total concurrency limit of 1,000 concurrent executions across all functions in an AWS Region. To support your specific account needs, you can request a quota increase · and configure function-level concurrency controls so that your critical functions don't experience throttling. This topic explains concurrency concepts and function scaling in Lambda. By the end of this topic, you'll be able to understand how to calculate concurrency, visualize the two main concurrency control options (reserved and provisioned), estimate appropriate concurrency control settings, and view metrics for further optimization.
AWS
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Orchestra
getorchestra.io › guides › configuring-reserved-concurrency-in-aws-lambda
Configuring reserved concurrency in AWS lambda | Orchestra
September 9, 2024 - By default, Lambda can scale automatically, up to a soft limit (which varies by account and region). Reserved concurrency is a configuration setting that allows you to specify the maximum number of concurrent executions for a Lambda function.