Debian. Automatic switching to a backup link?

Question

linux

There is a Gateway, VPN server, FTP server, 1C:Enterprise server and proxy server based on Debian. It is planned to conduct a backup line of Internet access. Accordingly, I want to configure application access to communication lines, approximately the following configuration:
IF both communication lines are available:
Main line:
Gateway,
VPN server,
FTP server,
1C: Enterprise server
Backup line:
Proxy server.
IF one of the lines is not available:
All applications switch to the remaining link, but the bandwidth for the proxy server must be reduced.
Can you tell me if there is software that can be used to set up such a scheme?

Answer 1

Such things are perfectly solved by PFSense