Has Anyone Migrated from Azure SQL to PostgreSQL Without Downtime?

For a flexible option, consider switching to vCore instead. You might need to collect some metrics to determine how many cores you’ll require, but it could be a better fit for your workload. The DTU model isn’t as flexible as vCores, and you mentioned your usage has spikes, so this might save you money too.

You should definitely be aware that Azure SQL DB has a lot of built-in advantages. It's a mature product with features like zero downtime scaling and managed authentication. If you're on the standard tier with 800 DTUs, consider looking into upgrading to the premium tier, which offers better performance for a lower cost. The premium P125 tier could give you around 2000 standard DTUs for about $450 a month, which might save you money in the long run.

Make sure to list out all your requirements and tasks for a successful migration. PostgreSQL is cheaper and reliable, but migration costs can take a while to break even on. It's worth considering if you're in it for the long haul, but you might not see quick savings.

A potential strategy for a smooth transition is to set up change data capture (CDC). This would keep your data in sync between the two databases while you switch over services. I recommend checking out more info on that if you're not familiar!

The complexity of your migration largely depends on how much development work is needed. Are you relying on any specific SQL Server functionalities? If not, that should make things easier since you'd be using an ORM like EF Core. Just make sure you have a solid plan for a zero-downtime transition!