Deploy-rs: Is there any way to prevent the output generated by deploy-rs being garbage collected?

Hey, guys. I’m using deploy-rs to deploy remote NixOS servers.

But there’s one problem that has been bothering me. The relevant output generated during each deployment is cleaned up after executing the garbage collector. Let me outline the detailed steps for you in the following console output:

# 1. prepare a `nixosConfigurations` in my `flake.nix`. Let's say `my-machine`.
$ cat flake.nix
# ...
{
  output = {
    nixosConfigurations = {
      my-machine = { ... };
    };
  };
}

# 2. deploy my-machine
$ deploy '.#my-machine'

# 3. check the outputs, and the outputs are there
$ ls -ld /nix/store/*my-machine*
-r--r--r--   1 root  nixbld   2277 Jan  1  1970 /nix/store/4fyd2zn6hgfirwiq6kly5llzjyx61yan-nixos-system-my-machine-23.05.20230917.5d017a8-activate-path.drv
dr-xr-xr-x   3 root  nixbld     96 Jan  1  1970 /nix/store/a1p8503jkadc48nyj9r3b5x4l73jl66b-nixos-system-my-machine-23.05.20230917.5d017a8-activate-rs/
dr-xr-xr-x  22 root  nixbld    704 Jan  1  1970 /nix/store/f11djylh3g2ggp53ix8p0hi9g0h7bln8-nixos-system-my-machine-23.05.20230917.5d017a8/
-r--r--r--   1 root  nixbld  40621 Jan  1  1970 /nix/store/g0i0macip6kimffcqdmbzhm5y2p0kivd-nixos-system-my-machine-23.05.20230917.5d017a8.drv
dr-xr-xr-x   3 root  nixbld     96 Jan  1  1970 /nix/store/gns0fn8v082rkd1wd3i56px8j4hw412w-nixos-system-my-machine-23.05.20230917.5d017a8-activate-path/
-rw-------   1 root  nixbld      0 Nov 15 10:33 /nix/store/gns0fn8v082rkd1wd3i56px8j4hw412w-nixos-system-my-machine-23.05.20230917.5d017a8-activate-path.lock
-r--r--r--   1 root  nixbld   2638 Jan  1  1970 /nix/store/l0ancxxsg0zy4957y7ifnm7n4lmjs6yq-activatable-nixos-system-my-machine-23.05.20230917.5d017a8.drv
dr-xr-xr-x  24 root  nixbld    768 Jan  1  1970 /nix/store/l28lknxb6lq0xn8nszvhq21hp0q8cdxf-activatable-nixos-system-my-machine-23.05.20230917.5d017a8/
-r--r--r--   1 root  nixbld   2027 Jan  1  1970 /nix/store/svw1vgkqagnwys068mccm3f6g8s375ah-nixos-system-my-machine-23.05.20230917.5d017a8-activate-rs.drv

# 4. collecting garbage, then all above outputs are cleaned up, which are not what I expect
$ nix-collect-garbage -d
$ ls -ld /nix/store/*my-machine* # nothing found
ls: cannot access '/nix/store/*myMachine*': No such file or directory

My quesition: “Is there any way to prevent the output generated by deploy-rs being garbage collected?”

Inspired by Preventing flake.nix written for remote targets from being garbage collected, I found the solution is to create a GC root.

  1. deploy-rs provides such an option - --keep-result. Yeah!
  2. enable following options in nix.conf:
keep-outputs = true
keep-derivations = true

Then, the essential output will be always placed in /nix/store, even after a garbage collection. :slight_smile: