Unexpected Charge on Free Tier Cosmos DB

Question

Hi all,

I have only one Cosmos DB Account in my subscription which I have set to be the "free tier" account with 1000 RU/s and 25 GB quota. I have set the Account to not exceed 1000 RU/s.

Now, having worked for a couple of hours on it (those hours distributed across 3 last weeks) and having created 3-4 NoSQL containers and manipulated maybe 10-20 really small documents in them, I was surprised to see that 4 cents were charged on the Cosmos DB resource.

I have checked the monitoring and it is nowhere to exceed the quota of 100 RU/s. We are talking about 100 RU per HOUR maybe (see the attached screenshot). There is some traffic on the metadata (probably from the monitor) but it's also well below the limit (and should be for free anyway). I've attached another screenshot on this.

What can be the reason for this unexpected cost? It is of course not about the 4 cents, but I want to understand if these are some fixed costs which I can ignore and whether the way RUs/storage are computed are way too conservative and the cosmos database will eat all my savings after inserting the first 1000 documents on the supposedly free tier database with the guarantee to actually not generate any cost?

Or are these current charges just an estimate for the month and they will be dropped at the end of the month if RU/s never exceeded 1000?

Thanks!

P.S. In case you are wondering why I haven't picked the first option "Limit the account's total provisioned throughput to the amount included in the free tier discount...". Whenever I pick this option and click save, it is saved as the second option "Allow the account's total throughput to be provisioned up to a custom account".

P.P.S. I have checked if the stockwatcher-db was created as free tier. Yes it was created with this flag (see the screenshot from the cli).

Answer 1

Hi Mykhailo Saienko,

Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.

We sincerely apologize for the inconvenience caused.

It appears that there are some unexpected charges on your Azure Cosmos DB free tier account. Let's review the potential causes and discuss the steps you can take to address this issue.

Firstly, in Azure Cosmos DB's Free Tier, users are granted up to 1,000 request units per second (RUs/s) and 25 GB of storage at no cost. However, if you exceed these limits, you will start incurring charges.

Even though you mentioned that your usage is well below the limit, there are a few things to consider:

• Request Throttling: Azure Cosmos DB automatically enforces request throttling when usage exceeds the allocated RUs. If your application tries to consume more RUs than the provisioned amount, the requests are rate-limited, resulting in a 429 Too Many Requests status code. This feature safeguards against unexpected costs by capping throughput at the provisioned level. https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/troubleshoot-dotnet-sdk-slow-request?tabs=cpu-new
• Monitoring and Alerts: Make sure to enable monitoring and set up alerts in Azure Monitor to keep track of your RU (Request Unit) usage. These alerts will let you know if you're getting close to the free tier limits so that you can take action and avoid extra charges.
• Fixed Costs: There might be some fixed costs associated with your Cosmos DB account, even if your usage is within the free tier limits. These could include costs related to metadata traffic or other background operations
• Estimates: The charges you see might be estimates for the month. If your RU/s never exceeded 1000RU/s, these charges could be dropped at the end of the month.

To better manage and control your usage, you can implement application-level rate limiting to ensure that the total operations per second sent to Azure Cosmos DB don’t surpass the allocated throughput.

Additionally, you can review the estimated cost and start creating your resources using the Azure Cosmos DB capacity calculator

Please refer to the below mentioned links for more information.

https://learn.microsoft.com/en-us/azure/cosmos-db/free-tier

https://learn.microsoft.com/en-us/azure/cosmos-db/nosql/troubleshoot-request-rate-too-large?tabs=resource-specific#how-to-investigate

https://learn.microsoft.com/en-us/azure/cosmos-db/limit-total-account-throughput

I hope, This response will address your query and helped you to overcome on your challenges.

If this answers your query, do click Accept Answer and Yes for was this answer helpful. And, if you have any further query do let us know.

Answer 2

Thank you for putting the links together.

Though the links do not immediately help in understanding the issue, it is good to know that these costs are not supposed to incur in a normal situation.

In the meantime, I have found in the detailed preliminary bill that the cost was indeed for 100 RU/s blocks for some reason. Maybe the throttling didn't work properly a couple of times.

Answer 3

Hi Mykhailo Saienko,

We sincerely apologize for the inconvenience caused and appreciate your understanding.

Thank you for confirming that you have received the detailed bill.

We would like to inform you that, any RU/s and storage usage exceeding 1000 RU/s and 25 GB will be billed at standard rates as outlined on the pricing page. The bill will not display a charge or line item for the free tier allocation of 1000 RU/s and 25 GB; only the usage beyond the free tier will be reflected.

Kindly ensure that the subscription limit is not exceeded. We hope this has addressed your query. If you found the answer helpful, please consider upvoting it, so that others experiencing the same thing can easily reference this. which might be beneficial to other community members reading this thread.

Thank you,