At my work, the backup appliances are typically physically located inside the LAN of our end users — much like other appliances such as routers, NAS devices or switches. Under normal circumstances that means that they are behind a NAT and are not reachable from the public Internet without a VPN or other tunneling mechanisms. For my employer’s customers, the Managed Service Provider (MSP), only being able to access their devices with direct physical access would be a major inconvenience.
Fortunately we’ve always provided a remote management feature called “Remote Web” for our customers: Remote Web lets them remotely access the device’s web interface as well as other services (mainly RDP, VNC, SSH), even when the device is behind a NAT.
Internally we call this feature RLY (pronounced: “relay”, like the owl, get it?). In this post, I’d like to talk about how we implemented the feature, what challenges we faced and what lessons we learned.