example: Use just for deterministic dataDir location

README.md

@@ -21,6 +21,10 @@ TODO
 - [x] Redis
 - [ ] ...
 
+## A note on process working directory
+
+The `dataDir` of these services tend to take *relative* paths, which are usually relative to the project root. As such, when you run these services using `nix run`, their data files are created relative to whichever directory you are in. If you want these data files to always reside relative to the project directory, instead of using `nix run` consider wrapping the process-compose packages in script, via either [mission-control](https://zero-to-flakes.com/mission-control/) module or a [justfile](https://just.systems/). The example uses the latter.
+
 ## Contributing
 
 - If you are adding a *new* service, see https://github.com/cachix/devenv/tree/main/src/modules/services for inspiration.

example/flake.nix

@@ -63,6 +63,10 @@
               machine.succeed("echo 'SELECT version();' | ${config.services.postgres.pg1.package}/bin/psql -h 127.0.0.1 -U tester ${dbName}")
             '';
           };
+
+        devShells.default = pkgs.mkShell {
+          nativeBuildInputs = [ pkgs.just ];
+        };
       };
     };
 }

example/justfile

@@ -0,0 +1,2 @@
+default:
+    nix run