Most residential ISPs would frown upon a large amount of upload traffic for a public service, and request that you switch to a business plan with a much lower contention ratio. Contention ratio is essentially the number of people the bandwidth is shared with. For example, if you have a 1Gbps connection with a contention ratio of 50:1 (common for residential ISPs), 50 people share the same 1Gbps bandwidth. That’s designed with the idea that not every user is using all their bandwidth at the exact same time. Constant uploads all day (like with a public proxy) breaks that assumption. Business plans usually have a contention ratio of 10:1 to 20:1.

The CEO of my ISP (Sonic) explicitly mentioned that they don’t like people hosting servers on their forum:

We don’t want folks hosting publically accessible servers on Sonic fiber. Primarily because while household consumption can be estimated and averaged, and is roughly limited by your ability to consume (how many TVs will you stream to, plus downloads and other activities, during the peak bandwidth usage time of the day?), when you host the usage is instead limited only by the REST of the world’s interest in what you’re offering.

So while a family of six with five 4K TVs might see peak average usage under 100Mbps if absolutely every device is on and all consuming full-scale content – a single Raspberry PI web server with a single video hosted on it might swamp a gigabit port if that video file is something everyone in the world wants to see.

While we can provide the fastest residential connection in America, it’s pricing relies upon typical use cases. That pricing is not sustainable if someone is hosting a popular website, sharing with neighbors, feeding a wireless ISP, acting as a TOR exit node, etc etc. Servers belong in data-centers (aka “the cloud”), for practical network scale as well as economic reasons.

They don’t block it though, and they’re fine with low-bandwidth things like Home Assistant, VPNs, etc.