Nix's substituter list is not a routing table

dtomvan · May 26, 2026, 4:04pm

By @NotAShelf, interesting article, talks about a tool called ncro they made to help fix nix’s multi-cache slowness problem.

srestegosaurio · May 28, 2026, 10:07pm

Pretty cool!!

It may help reducing the “I pull a lot of random flakes” problem.

Btw: nice to see some systemd service hardening.

bbigras · June 8, 2026, 5:24pm

Can ncro handle flake.nix that have extra-substituters? Like this:

github.com/bbigras/nix-config

flake.nix

c75b2ff32


      
          nixConfig = rec {
            extra-substituters = [
              "https://bbigras-nix-config.cachix.org?priority=1"
              "https://nix-community.cachix.org?priority=2"
            ];
            extra-trusted-substituters = extra-substituters;
            extra-trusted-public-keys = [
              "bbigras-nix-config.cachix.org-1:aXL6Q9Oi0jyF79YAKRu17iVNk9HY0p23OZX7FA8ulhU="
              "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
            ];
          };

dtomvan · June 8, 2026, 7:42pm

Yes, but you’ll lose the abilty to race those substituters in parallel. Those caches will be used only after substituters is exhausted though, so yeah, that’s viable if you don’t mind that those extra substituters may be handled slowly as if you’re not using ncro at all.