If the primary write region fails, applications that write to the database must use a different connection string to continue to use the service. = NO

You do not need to use a different connection string to continue to use the service if the primary write region fails.  This is because Azure Cosmos DB supports automatic failover, which means that it will automatically switch the primary write region to another region in case of a regional o utage 2 .  The application doe s not need to change the connection string or specify the failover priority 3 .  The connection string contains a list of all the regions associated with your account, and Azure Cos mos DB will route the requests to the appropriate region based on the availability and latency 1 .

The primary Read-Only SQL Connection String and the Secondary Read-Only SQL Connection String will connect to different regions from an application running in the East US Azure region = Yes

The primary read-only SQL connection string and the secondary read-only SQL connection string will connect to different regions from an application running in the East US Azure region. This is because the primary read-only SQL connection string contains the endpoint for the East US region, which is the same as the primary write region. The secondary read-only SQL connection string contains the endpoint for the West US region, which is the additional read region. Therefore, if an application running in the East US Azure region uses these connection strings, it will connect to different regions depending on which one it chooses.

Applications can choose from which region by setting the PreferredLocations property within their connection properties = Yes

Applications can choose from which region by setting the PreferredLocations property within their connection properties.  This property allows you to specify a list of regions that you prefer to read from based on their proximity to your application 2 .  Azure Cosmos DB will route the requests to the appropriate region based on the availability and latency 1 .  You can also set the ApplicationRegion property to the region where your application is deployed, and Azure Cosmos DB will automatically populate the PreferredLocations property based on the geo-proximity from that location 1 .