We wrote our own image processing, resizing, and snapshotting service in Go to allow our clients to send photos and GIFs to each other. Files are stored in S3, resized on the fly using OpenCV, and then cached in GroupCache before being served to clients.
Go allows it all to be quite fast and efficient, and entirely non-blocking on uploads!
The first time I actually started using Go was for software on our devices. So on our hotspots we have some custom software running in the firmware. For the first device, that was actually completely built by our manufacturer. But for the second generation most of the parts are built by us in-house and we needed a way to quickly develop software for the device. But we don't have any C programmers in-house, so we were actually looking for something that basically sits in between the friendliness of Ruby, but the performance and the ability to be deployed on an embedded system which you get with C. That's basically what led us to Go and it's been awesome for that. It works so well and so great. Since it works so great, it pushed us into looking into whether we should start using this for some backend services as well.
For some of our more taxing parts of our applications, something able to handle high I/O load quickly and with fast processing is needed. Go has completely filled that gap, allowing us to break down walls that would've been completely impossible with other languages.
Simple but powerful language to create system and network tools that we utilize. Compiled program makes it easy to deploy due to no complex dependencies.
We use golang to create image and video preprocessor, utility for health check + autoscaling and many others