What can you do with the Azure Cosmos DB free tier?

Beginning of March 2020, Microsoft announced the availability of a free tier of Azure Cosmos DB (see Azure Cosmos DB Free Tier is now available)

"When free tier is enabled on an Azure Cosmos DB account, you’ll get the first 400 RU/s and 5 GB of storage for free for the lifetime of the account. Additionally, when using shared throughput databases, you can create up to 25 containers that share 400 RU/s at the database level. There’s a maximum of one free tier account per Azure subscription and you must opt-in when creating the account."

But maybe you are wondering what you can actually do with 400 RU/s? Request Units per second (RU/s) represent the "cost" of a request in terms of CPU, memory and IO. In Azure Cosmos DB you can provision "performance" upfront by setting RU/s at database level, collection level or both. It is however also possible to create Azure Cosmos DB containers and databases in autoscale mode  Containers and databases configured in auto scale mode will automatically and instantly scale the provisioned throughput based on your application needs without impacting the availability, latency, throughput, or performance of the workload globally

I can highly recommend you to take a look at the Microsoft Ignite 2019 session - A developer's guide to Azure Cosmos DB, from onboarding to going live in production . The code samples from session are available on Github - https://github.com/deborahc/cosmos-perf-tips

References:

• Choosing the right partition key for cost and performance with Azure Cosmos DB (Youtube 00:14:27)
• Find the  request unit (RU) charge in Azure Cosmos DB
• April 2020 query updates in Azure Cosmos DB
• Free Tier Cosmos DB ARM template
• Raven DB vs Cosmos DB - article is a little outdated due to a number of new updates to Cosmos DB but still quite interesting