Lava farming is a renewable way, added in 1.17, to farm lava using cauldrons and dripstones. The lava then can be sold to villagers for emeralds, used for smelting, or for turning into obsidian.
The basic concept
- Place a cauldron.
- Place a solid block (dripstone blocks are best) 2 blocks above the cauldron.
- Place pointed dripstone 1 block above the cauldron.
- Place a lava source over the dripstone block and make sure it doesn't flow anywhere.
- Wait for the cauldron to fill up.
And you're done! The cauldron will slowly keep filling up with lava! It will take about 20 minutes on default tick speed (1), but if you place more next to each other, then you can get a lot of lava very quickly for all your smelting and obsidian needs.