MySQL – Does AutoIncrement ID Degrade Performance?

The only performance hit I can see is on the INFORMATION_SCHEMA database (See my post How is INFORMATION_SCHEMA implemented in MySQL?)

If you have queries that poll for the existence of tables, gets the table sizes (Example: See my post MySQL Workbench Database Sizes), and things of this nature, MySQL will spend time sifting through the OS for such metadata. Getting metadata on InnoDB tables and partitioned MyISAM tables will make the INFORMATION_SCHEMA take the worst hit as it must open many file handles.

Other than that, you regular queries on your working dataset should be fine.

Since Zapier is coming in from outside your instance, a possible cause of your problem is the security group for your instance. Most ports on EC2 instances (except the SSH port) are normally blocked by default unless you explicitly open them.

So you would need to open the mysql port 3306 on your instance up to the ip address Zapier is coming in from. (preferably you would not open it up to everyone in the world.)

See Using Amazon RDS/EC2 on the Zapier site, starting from the section where it says Can't Connect to My Database. They continue on to provide specific instructions for the security group settings.

You will also probably need to grant permission on the database using the mysql GRANT command to the user coming in from the Zapier ip address.

Something like this should work :

GRANT ALL PRIVILEGES
ON mydb.*
TO 'user'@'54.86.9.50'
IDENTIFIED BY 'newpassword';

Or you can allow that user to come in from any ip adress like this:

GRANT ALL PRIVILEGES
ON mydb.*
TO 'user'@'%'
IDENTIFIED BY 'newpassword';

(Incoming requests would still be limited to Zapier ip addresses due to the security group settings.)