> BTW, we're preparing to move a postgres database that's a few TB from Heroku to AWS RDS. The catch is that we can't afford more than a few minutes of downtime

> BTW, we're preparing to move a postgres database that's a few TB from Heroku to AWS RDS. The catch is that we can't afford more than a few minutes of downtime. Would it be ok to serve stale data for an extended amount of time? If so then you could modify your application to write to AWS RDS but to keep reading from Heroku. Then you start copying over the data from Heroku to AWS RDS, and once the copying is done then you point your application to read from AWS RDS. Another thing: If your tables have foreign key constraints then you need to create the tables in the new DB without them first, since the writes coming to the new DB could be referencing data from the old DB which have not yet been copied over. Once you’ve completed copying the data over you add the FK constraints to the new DB. Depending on how your application was made this could be a problem or it could be ok.