You have been frustrated because of cannot find a ISO file on official website. Literally windows officially didn't provide downloadable ISO file. Visual studio components need to updated frequently and it verifies installs by using Authenticode signatures to prevent malicious attacks that is why developer community designed the online based installation. We might not take on that reason, when you have unreliable internet connection it may toughest job to download via online. Alternatively VS developer community offers offline installer by considering slow or unstable internet connection.
No worry you can try the offline installer to your ISO file from the downloaded files, for the later use. I hope you might gone through visual studio installation requirement, If you're having windows 8.0 or lower version this article precisely not for you.
Download Visual Studio 2017 ISO
Before we get started, you must download desirable edition of Visual studio.
1) Once download finished go to the downloaded location and copy the file name including .exe extension. In the address bar type cmd and hit enter. It brings up the CMD ( Command Prompt ) make sure it opens on downloaded location or you may moved that file different location if so follow above procedure on the setup file location.
2) You need internet connection to download the offline installation files. Here i have used to community edition change it according to you need. Put command on CMD if you don't prefer any language.
vs_community.exe --layout c:\path_to_save_file
to choose another language replace
en-US your choice
vs_community.exe --layout c:\path_to_save_file --lang en-US
In case download interuppted, don't panic use the same command when you start create without changing the folder. Because this method has resume support. On command exection it verfies wherther the file exists then download.
3) All done.