Developers like to know when things go wrong in applications. It is an easy and simple solution to send an email when a bad error occurs. Things can go wrong easily in Cosmos Db, one of the most common error you will get from Cosmos DB is “Request rate too large (429)” exception. This error says that you do not have enough request units to run a query. This error usually occurs in peak times. Usually cause of getting 429 errors is the configuration of Request Units settings. You need to scale up your application or optimize your queries.
It takes more time to retrieve data from Cosmos DB when error 429 occurs. You should get notification when this occurs, but you do not want to get an email each time it occurs either. 1- 5% of requests with 429 is acceptable. You can always open the Cosmos DB Monitoring tools and keep eye on it, or you can create Cosmos DB Alerts to get emails.
Click through for a demonstration of how to use Cosmos DB Alerts.