Following up on a recent thread that the simple netwatch is not enough for me to verify if my internet connections are working, I stumbled upon /tool fetch. I wonder if I can create a script to download a file from my servers to verify whether the connections are working.

Hurdles I've encountered so far, i cannot find a way to restrict the interface from which to run fetch, second I can't seem to figure out how to judge success or failure while in a script.

Any help would be greatly appreciated.

fetch will always follow routing path to get to host to download/upload files. So, using this you can only check if router has any connectivity.

To determine success or failure of fetch, use :do { } on-error={ } ; Instead of the script stopping, it continues if fetch fails.
This is a sample of my program the sends all the files to an FTP server to back them up.

:set ftpresults "Sucessful"
:do { /tool fetch address=$ftpserver port=$ftpport src-path=$locfilename upload=yes user=$ftpuser mode=ftp password=$ftppw dst-path=$remfilename keep-result=yes } \
on-error={ :set failcount ( $failcount + 1 ) ; :set ftpresults "Failed"; }

Good guidance

I`m wondering possibility of routeros if I use HTTP POST to interact with 3rd party system instead of API, because routeros can`t call 3rd party API. In other word, 3rd party web server will hear http post to get information from routeros. Routeros will POST queue stats over http to this web server. Server side it`s ok to handle thousands of POST requests in seconds but how about routeros. How many simultaneous http post can routeros handle? Does any one have such experience?

I just tested http post. please see below.
I sent 100 post request with one shot using script But all 100 requests take 2 minutes to complete. I included log command at the start and end of the script. You can that it took almost minutes. Delay from my router to server is ~279ms. Bandwidth is really enough. This small post requests take only few kbps. When do fetch, CPU was max 1% on fetcher process. Router is hap ac (720 MHz). Memory was always 99MB free out of 128MB.
What can be the possible bottleneck?