> This seems like a HA-Proxy problem. They ought to maintain support for geriatric TLS versions on a dedicated release branch connected to a support-model that nudges their client into updating by increasing their fees for maintaining that system. Not doing so means the vendor is part of the problem why we have slower adoption rates for 1.3 than we could otherwise have.

If I understand what you're suggesting, it's that HAProxy should have their current public releases support only TLS 1.2 and 1.3, and a paid release that supports TLS 1.0-1.3 and that would encourge adoption of 1.3?

I would expect those users who have a requirement for TLS 1.0 to stay on an old public free release that supports TLS 1.0-1.2 in that case. If upgrading to support 1.3 would mean dropping a requirement or paying money, who would do it? How does that increase adoption vs making it available with all the other versions in the free release? Some people might reevaluate their requirements given the choices, but if anything that pushes abandonment of TLS 1.0 more than adoption of TLS 1.3.

I no longer have to support this kind of thing, but when you require dropping the old thing at the same time as supporting the new thing, you're forcing them to choose, and unless the choice is very clear, you'll have a large group of people that pick to support the old thing. IMHO, the differences between TLS 1.0,1.1, and 1.2 aren't so big that you can claim it's too hard to support them all, and dropping support for 1.0 and 1.1 on the server doesn't gain much security. 1.2 to 1.3 is a bigger change, if you wanted to only support 1.3, that's an argument to have, but I don't think that's a realistic position for a general purpose proxy at this point in time (it would certainly be a realistic configuration option though).