It turns out Azure mobile service is way more powerful than you think. I setup a simple mobile service table to hold some incoming logs.
on the table itself, I created one node.js API for insert, basically insert a timestamp in long named dt. (I found this very useful for you to delete the old data , like logs week ago)
then every incoming logs will be applied with the timestamp. now create another scheduler to run daily and check to delete old logs
and config it to run daily
then in the log you will see the daily run