How to actually get measurement data from Modbus Gateway


I'm very new to Modbus and still trying to understand how we can get data from a measuring instrument.

We're looking at the instrument here: Measuring instrument - EEM-MA770-EIP

We would them use AWS Sitewise to communicate with the measuring instrument: AWS Sitewise Modbus config

This device would be located at a site and collect measurements. I understand that it is able to function as a Modbus gateway, but where I am confused is how the data actually flows. Does the gateway device push data to the Sitewise server? Or, does the Sitewise server pull from the gateway?

If the latter, I assume the gateway would need a public IP address?
The data is pushed from the AWS IoT SiteWise gateway to the cloud (this is how all cloud communications works, otherwise it would be an IT nightmare of setting up firewalls and/or public IP's, etc.). Note that you need a physical device to run the AWS IoT SiteWise gateway software on site, such as a PC, embedded computer, industrial gateway, Raspberry Pi, BeagleBone, etc.

Take a look at the "How AWS IoT SiteWise works" section here:

From the above link:
Use AWS IoT SiteWise gateway software that runs on any platform that supports AWS IoT Greengrass, such as common industrial gateways or virtual servers. This software can read data directly from on-site servers over protocols such as the OPC-UA protocol. You can connect up to 100 OPC-UA servers to a single AWS IoT SiteWise gateway. You can also read data over the Modbus TCP and Ethernet/IP (EIP) protocol.