Basic usage of devShell

[peedrr]

TL;DR: Is it always necessary to nix run before opening a dev shell?

Firstly, thank you! My stack is Postgres, Redis and Nats, so it looks like I'm well covered straight out of the box.

I'm right at the beginning of my journey with services-flake so please excuse the "page 1" question! (And I'm only on about page 2 with flakes!)

The flake gets loaded by direnv

Here's my flake so far:

{
  description = "Testing services-flake with Redis";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

    # services-flake
    process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
    services-flake.url = "github:juspay/services-flake";
    flake-parts.url = "github:hercules-ci/flake-parts";
  };

  outputs = inputs:
    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        # import the flake module
        inputs.process-compose-flake.flakeModule
      ];
      systems = inputs.nixpkgs.lib.systems.flakeExposed;
      perSystem = { pkgs, config, ... }: {
        # Create the process-compose configuration, importing services-flake
        process-compose."default" = {
          imports = [
            inputs.services-flake.processComposeModules.default
          ];
          # Define the services to be started
          services = {
            redis."r1".enable = true;
          };
        };

        # DevShell
        devShells.default = pkgs.mkShell {
          inputsFrom = [
            config.process-compose."default".services.outputs.devShell
          ];
        };
      };
    };
}

When I cd into the directory I seem to already have packages, e.g. redis-cli, but redis-server is not running:

$ redis-cli
Could not connect to Redis at 127.0.0.1:6379: Connection refused
not connected>

Obviously nix run then gives me Process Compose. Opening another shell to the same directory then allows me to connect to the Redis server. Is this the intended usage? Is it possible to nix develop and then start Process Compose as needed? (Without typing nix run?)

[peedrr]

I'm going to close this. I've only just found out the direnv makes nix develop redundant as I'm already in a "dev shell"! So nix run is the way to manually start Process Compose!!

Every day is a school day!

[shivaraj-bh]

Having services up automatically when you are in the devShell is nice. #312 in combination with #384 should aid in solving this in a reliable fashion.

Also, DX can be much nicer if you combine that with services listening on unix domain sockets instead of TCP. This eliminates the global state (of binding to the port). See an example of this in https://github.com/juspay/todo-app/blob/master/nix/services/default.nix.

[shivaraj-bh]

Unrelated, but since there is a mention of background services, #354 will allow one to import homeModules instead of the usual processComposeModules and enable the same services via systemd (on Linux) or launchd (on macOS) in home-manager configuration. Note that using homeModules will be global to the user and not local to the project devShell.

Aside: solving #354 will make it easier to support more backends in the future.