So store sqlite on S3. Start a new lambda (or similar) per user, download the db from sqlite and write to it and upload it again. And making sure there can neve

So store sqlite on S3. Start a new lambda (or similar) per user, download the db from sqlite and write to it and upload it again. And making sure there can never be more than 1 function running per user (to avoid two lambdas editing the same database). Seems a bit fragil but I might be wrong.