Ask HN: How to load-balance two 1 Gbps connections with a failover?

Hi! I used to have a single 1 Gbps connection running from ISP A. Unfortunately, it has been spotty, sometimes dropping out for as much as 30 minutes. 1 Gbps fiber is not expensive where I live (~$15/month), so I've decided to just get a second 1 Gbps fiber from ISP B. Since I can't cancel the service from ISP A just yet due to the agreement length (doesn't make financial sense to pay the early cancellation fee), I ended up with two FTTH setups.

I'd like to combine those two connections to:

1. Have a quick failover in case either fiber link fails.

2. Load balance them for increased maximum throughput, assuming different connections. Not interested in an overly complicated remote setup for combining bandwidth, since neither of the ISPs supportss MLPPP and I have no need for higher speeds, anyway. In an ideal scenario, two different machines would be able to download at 800-900 Mbps each (which is what I usually get from each connection), saturating both ISP A and ISP B connections. Meaning that the router would ideally be able to process 2 Gbps of traffic in total.

3. Have the new setup be quiet and small, it'll live in small-ish cabinet next to the ISP routers (more on that below) and I definitely don't have the space there to stuck my old PC with PFSense in there.

4. I need a reliable, business-grade solution that will require minimal/no maintenance and will sit there working for years and years. It's unacceptable for my connection to keep cutting off on key meetings, where I'm often the person presenting.

Additional information: No need for it to have Wi-fi AC, I have a separate AC, no need for LTE capabilities, too. Upload isn't as important, I don't do a lot of hosting here nowadays, everything moved to the cloud. If it's relevant, both links are 300 Mbps up, so not symmetrical. The configuration and device doesn't have to be super end-user-friendly (would be nice, though, of course), I'm not a networking expert, but I've been working in IT for quite a bit and I'm sure I can handle some basic network configuration if required (I have some experience with configuring Cisco switches and routers). Hopefully it won't cost that much, but I'm willing to spend upwards of $1000 on this if there is a good reason, as this will be used for my only source of income.

Now, I've done a plenty of research and there are a ton of multi-WAN routers, e.g. TP-Link TL-R605, Synology RT2600ac or business-grade Linksys LRT224 and the Peplink Balance line.

I would've ordered one of these by now, but my key question is, which I wasn't able to easily research: Can the WAN connection be a cable to a LAN port on a router from the ISP? Because I don't have ISP-provided WAN Ethernet cables coming out of the wall and that's what has always been going into my routers' WAN port. I have two fiber cables coming out of the wall, connected to a router from the ISP each and those have regular LAN GE ports. I've asked the new ISP and they said I'm required to be using their fiber router, otherwise my 8h internet-back-up SLA and other maintenance services in case of issues don't apply anymore.

What kind of a device will allow me to connect it via cat6 Ethernet to two different routers on different subnets? Is it what all those "WAN" ports on the multi-WAN routers expect already that I'll do?

The Peplink Balance line looks it has all of the features I need, but it's been quite difficult for me to understand what the total throughput is if I don't need a firewall on it. If the Balance One supports up to 5 WAN connections, it means it can handle load-balancing 5 Gbps of traffic? Doesn't seem so, it looks the actual throughput is the "Stateful Firewall Throughput", which would then be barely 600 Mbps... Which router would support 2 Gbps total throughput to be able to saturate both ISPs? If 2 Gbps is not possible within a reasonable budget, I can settle on 1 Gbps, that's plenty for me, too.

Thanks!