The host entry in the config file of Galaxy only refers to the location the Galaxy web process(http) will be listening on.
Galaxy itself does not provide any FTP server functionality. You will have to setup a FTP server if you want this capability. Have a look a this documentation https://wiki.galaxyproject.org/Admin/Config/UploadviaFTP
The ftp_upload_site could thus be ftp://server2 (the address you would use in e.g. filezilla), whereas your Galaxy instance is running on http://server1:8080
In addition, you do not necessarily need a ftp server on your local instance. You can upload small datasets using the web uploader and for bigger files use the data library dataset import functions https://wiki.galaxyproject.org/Admin/DataLibraries/UploadingLibraryFiles
ftp_upload_site indicates the URL to your ftp server. Just edit is and enter a string with the proper URL. This string is only used to inform you users where to upload the data. So in the end it's an information that is displayed to the user and has not functional usage.
Thanks for your answer! I got it.
But I have another problem with host, what should I fill in the host when I upload my data to the local galaxy?The default host: 127.0.0.1:8080 ?
Frankly, I can not understand the documentation very well, so could you give me an example? Thank you again !