Right now it looks like it’s either going to be a hard Brexit, or a Brexit which isn’t going to be a Brexit.

For a hard Brexit, there needs to be a proper border between the EU and the United Kingdom, where people and goods can be checked.

The only land border between the EU and the UK is on the island of Ireland. According to the Good Friday Agreement/Belfaster Treaty, this border can not be closed.
If the Irish or the British close this border, they will be violating an internationally guaranteed treaty, which has secured peace in Ireland and the British mainland since 1998.
If neither of these two countries close this border, who will?

British Brexit hardliners are well aware of this reality. That’s why they keep saying, that there will be no hard border on the island of Ireland.

Can the EU violate an internationally guaranteed treaty by closing their Irish land border with the UK? Does the EU want to get involved in the Northern Ireland conflict, which is capable of being reignited?