Cargo.toml

@@ -44,9 +44,18 @@ version = "1.28.1"
 features = [
 	"fs",
 	"io-util",
+	"io-std",
 	"macros",
 	"process",
 	"rt",
 	"rt-multi-thread",
 	"sync",
 ]
+
+[[bin]]
+name = "colmena"
+path = "src/main.rs"
+
+[lib]
+name = "colmena"
+path = "src/lib.rs"

src/error.rs

@@ -55,6 +55,9 @@ pub enum ColmenaError {
     #[snafu(display("Unexpected active profile: {:?}", profile))]
     ActiveProfileUnexpected { profile: Profile },
 
+    #[snafu(display("Invalid JSON from activation program: {}", error))]
+    InvalidActivationProgramJson { error: serde_json::Error },
+
     #[snafu(display("Could not determine current profile"))]
     FailedToGetCurrentProfile,
 
@@ -64,6 +67,12 @@ pub enum ColmenaError {
     #[snafu(display("Don't know how to connect to the node"))]
     NoTargetHost,
 
+    #[snafu(display(
+        "Don't know how to deploy node: {} -- does your system type support deployment?",
+        node_name
+    ))]
+    UndeployableHost { node_name: String },
+
     #[snafu(display("Node name cannot be empty"))]
     EmptyNodeName,
 

src/lib.rs

@@ -0,0 +1,16 @@
+#![allow(dead_code)]
+
+mod cli;
+mod command;
+mod error;
+mod job;
+mod nix;
+mod progress;
+mod troubleshooter;
+mod util;
+
+pub use nix::host::generic::Request as GenericRequest;
+pub use nix::host::generic::Response as GenericResponse;
+pub use nix::host::CopyOptions;
+pub use nix::key::{Key, UploadAt};
+pub use nix::store::StorePath;

src/nix/hive/eval.nix

@@ -38,19 +38,25 @@ let
     else if uncheckedHive ? network then uncheckedHive.network
     else {};
 
+  uncheckedRegistries = if uncheckedHive ? registry then uncheckedHive.registry else {};
+
   # The final hive will always have the meta key instead of network.
   hive = let
     userMeta = (lib.modules.evalModules {
       modules = [ colmenaOptions.metaOptions uncheckedUserMeta ];
     }).config;
 
+    registry = (lib.modules.evalModules {
+      modules = [ colmenaOptions.registryOptions  { registry = uncheckedRegistries; } ];
+    }).config.registry;
+
     mergedHive =
       assert lib.assertMsg (!(uncheckedHive ? __schema)) ''
         You cannot pass in an already-evaluated Hive into the evaluator.
 
         Hint: Use the `colmenaHive` output instead of `colmena`.
       '';
-      removeAttrs (defaultHive // uncheckedHive) [ "meta" "network" ];
+      removeAttrs (defaultHive // uncheckedHive) [ "meta" "network" "registry" ];
 
     meta = {
       meta =
@@ -58,7 +64,7 @@ let
         then userMeta // { nixpkgs = <nixpkgs>; }
         else userMeta;
     };
-  in mergedHive // meta;
+  in mergedHive // meta // { inherit registry; };
 
   configsFor = node: let
     nodeConfig = hive.${node};
@@ -112,14 +118,23 @@ let
   in mkNixpkgs "meta.nixpkgs" nixpkgsConf;
 
   lib = nixpkgs.lib;
-  reservedNames = [ "defaults" "network" "meta" ];
+  reservedNames = [ "defaults" "network" "meta" "registry" ];
 
-  evalNode = name: configs: let
+  evalNode = name: configs:
+  # Some help on error messages.
+  assert (lib.assertMsg (lib.hasAttrByPath [ "deployment" "systemType" ] hive.${name})
+  "${name} does not have a deployment system type!");
+  assert (lib.assertMsg (builtins.typeOf hive.registry == "set"))
+    "The hive's registry is not a set, but of type '${builtins.typeOf hive.registry}'";
+  assert (lib.assertMsg (lib.hasAttr hive.${name}.deployment.systemType hive.registry)
+    "${builtins.toJSON (hive.${name}.deployment.systemType)} does not exist in the registry of systems!");
+  let
+    # We cannot use `configs` because we need to access to the raw configuration fragment.
+    inherit (hive.registry.${hive.${name}.deployment.systemType}) evalConfig;
     npkgs =
       if hasAttr name hive.meta.nodeNixpkgs
       then mkNixpkgs "meta.nodeNixpkgs.${name}" hive.meta.nodeNixpkgs.${name}
       else nixpkgs;
-    evalConfig = import (npkgs.path + "/nixos/lib/eval-config.nix");
 
     # Here we need to merge the configurations in meta.nixpkgs
     # and in machine config.
@@ -139,17 +154,19 @@ let
       in
         lib.optional (!hasTypedConfig && length remainingKeys != 0)
         "The following Nixpkgs configuration keys set in meta.nixpkgs will be ignored: ${toString remainingKeys}";
-    };
+      } // lib.optionalAttrs (builtins.hasAttr "localSystem" npkgs || builtins.hasAttr "crossSystem" npkgs) {
+        nixpkgs.localSystem = lib.mkBefore npkgs.localSystem;
+        nixpkgs.crossSystem = lib.mkBefore npkgs.crossSystem;
+      };
   in evalConfig {
-    inherit (npkgs) system;
+    # This doesn't exist for `evalModules` the generic way.
+    # inherit (npkgs) system;
 
     modules = [
       nixpkgsModule
       colmenaModules.assertionModule
-      colmenaModules.keyChownModule
-      colmenaModules.keyServiceModule
       colmenaOptions.deploymentOptions
-      hive.defaults
+      (hive.registry.${hive.${name}.deployment.systemType}.defaults or hive.defaults)
     ] ++ configs;
     specialArgs = {
       inherit name;
@@ -179,6 +196,10 @@ let
     "allowApplyAll"
   ];
 
+  serializableSystemTypeConfigKeys = [
+    "supportsDeployment" "activationProgram" "protocol"
+  ];
+
 in rec {
   # Exported attributes
   __schema = "v0";
@@ -190,5 +211,9 @@ in rec {
   evalSelected =             names: lib.filterAttrs (name: _: elem name names) toplevel;
   evalSelectedDrvPaths =     names: lib.mapAttrs    (_: v: v.drvPath)          (evalSelected names);
   metaConfig = lib.filterAttrs (n: v: elem n metaConfigKeys) hive.meta;
-  introspect = f: f { inherit lib; pkgs = nixpkgs; nodes = uncheckedNodes; };
+  # We cannot perform a `metaConfigKeys`-style simple check here
+  # because registry is arbitrarily deep and may evaluate nixpkgs indirectly.
+  registryConfig = lib.mapAttrs (systemTypeName: systemType:
+    lib.filterAttrs (n: v: elem n serializableSystemTypeConfigKeys) systemType) hive.registry;
+  introspect = f: f { inherit lib; pkgs = nixpkgs; inherit nodes; };
 }

src/nix/hive/mod.rs

@@ -15,7 +15,7 @@ use validator::Validate;
 use super::deployment::TargetNode;
 use super::{
     Flake, MetaConfig, NixExpression, NixFlags, NodeConfig, NodeFilter, NodeName,
-    ProfileDerivation, SerializedNixExpression, StorePath,
+    ProfileDerivation, RegistryConfig, SerializedNixExpression, StorePath,
 };
 use crate::error::{ColmenaError, ColmenaResult};
 use crate::job::JobHandle;
@@ -87,6 +87,8 @@ pub struct Hive {
     nix_options: HashMap<String, String>,
 
     meta_config: OnceCell<MetaConfig>,
+
+    registry_config: OnceCell<RegistryConfig>,
 }
 
 struct NixInstantiate<'hive> {
@@ -140,6 +142,7 @@ impl Hive {
             impure: false,
             nix_options: HashMap::new(),
             meta_config: OnceCell::new(),
+            registry_config: OnceCell::new(),
         })
     }
 
@@ -158,6 +161,17 @@ impl Hive {
             .await
     }
 
+    pub async fn get_registry_config(&self) -> ColmenaResult<&RegistryConfig> {
+        self.registry_config
+            .get_or_try_init(|| async {
+                self.nix_instantiate("hive.registryConfig")
+                    .eval()
+                    .capture_json()
+                    .await
+            })
+            .await
+    }
+
     pub fn set_show_trace(&mut self, value: bool) {
         self.show_trace = value;
     }
@@ -201,6 +215,9 @@ impl Hive {
     ) -> ColmenaResult<HashMap<NodeName, TargetNode>> {
         let mut node_configs = None;
 
+        log::info!("Enumerating systems...");
+        let registry = self.get_registry_config().await?;
+
         log::info!("Enumerating nodes...");
 
         let all_nodes = self.node_names().await?;
@@ -234,29 +251,61 @@ impl Hive {
             self.deployment_info_selected(&selected_nodes).await?
         };
 
+        for node_config in &node_configs {
+            if let Some(system_type) = node_config.1.system_type.as_ref() {
+                let Some(system_config) = registry.systems.get(system_type) else {
+                    // TODO: convert me to proper error?
+                    log::warn!("'{:?}' is not a known system type in the registry, double check your expressions!", system_type);
+                    return Err(ColmenaError::Unknown {
+                        message: "unknown system type".to_string(),
+                    });
+                };
+
+                if !system_config.supports_deployment {
+                    return Err(ColmenaError::UndeployableHost {
+                        node_name: node_config.0.to_string(),
+                    });
+                }
+            }
+        }
+
         let mut targets = HashMap::new();
         let mut n_ssh = 0;
         for node in selected_nodes.into_iter() {
             let config = node_configs.remove(&node).unwrap();
 
-            let host = config.to_ssh_host().map(|mut host| {
-                n_ssh += 1;
-
-                if let Some(ssh_config) = &ssh_config {
-                    host.set_ssh_config(ssh_config.clone());
-                }
-
-                if self.is_flake() {
-                    host.set_use_nix3_copy(true);
-                }
-
-                host.upcast()
-            });
-            let ssh_host = host.is_some();
-            let target = TargetNode::new(node.clone(), host, config);
-
-            if !ssh_only || ssh_host {
+            if let Some(system_type) = config.system_type.as_ref() {
+                log::debug!(
+                    "Using generic host (system_type: {}) for node {}",
+                    system_type,
+                    node.0
+                );
+                let system_config = registry.systems.get(system_type).unwrap();
+                let mut generic_host = config.to_generic_host(system_config)?;
+                generic_host.connect().await?;
+                let target = TargetNode::new(node.clone(), Some(Box::new(generic_host)), config);
                 targets.insert(node, target);
+            } else {
+                log::debug!("Using SSH host for node {}", node.0);
+                let host = config.to_ssh_host().map(|mut host| {
+                    n_ssh += 1;
+
+                    if let Some(ssh_config) = &ssh_config {
+                        host.set_ssh_config(ssh_config.clone());
+                    }
+
+                    if self.is_flake() {
+                        host.set_use_nix3_copy(true);
+                    }
+
+                    host.upcast()
+                });
+                let ssh_host = host.is_some();
+                let target = TargetNode::new(node.clone(), host, config);
+
+                if !ssh_only || ssh_host {
+                    targets.insert(node, target);
+                }
             }
         }
 

src/nix/hive/options.nix

@@ -98,6 +98,14 @@ with builtins; rec {
   in {
     options = {
       deployment = {
+        systemType = lib.mkOption {
+          description = mdDoc ''
+            System type used for this node, e.g. NixOS.
+          '';
+          default = "nixos";
+          # TODO: enum among all registered systems?
+          type = types.str;
+        };
         targetHost = lib.mkOption {
           description = mdDoc ''
             The target SSH node for deployment.
@@ -126,6 +134,13 @@ with builtins; rec {
           type = types.nullOr types.str;
           default = "root";
         };
+        connectionUri = lib.mkOption {
+          description = mdDoc ''
+            Connection options given to the activation program.
+          '';
+          type = types.str;
+          default = "ssh://localhost";
+        };
         allowLocalDeployment = lib.mkOption {
           description = mdDoc ''
             Allow the configuration to be applied locally on the host running
@@ -218,6 +233,58 @@ with builtins; rec {
       };
     };
   };
+  # Options for a registered system type
+  systemTypeOptions = { name, lib, ... }: let
+    inherit (lib) types;
+    mdDoc = lib.mdDoc or lib.id;
+  in
+  {
+    options = {
+      evalConfig = lib.mkOption {
+        description = mdDoc ''
+          Evaluation function which share the same interface as `nixos/lib/eval-config.nix`
+          which can be tailored to your own usecases or to target another type of system,
+          e.g. nix-darwin.
+        '';
+        type = types.functionTo types.unspecified;
+      };
+      supportsDeployment = lib.mkOption {
+        description = mdDoc ''
+          Whether this system type supports deployment or not.
+
+          If it supports deployment, it needs to have appropriate activation code,
+          refer to how to write custom activators.
+        '';
+        default = name == "nixos";
+        defaultText = "If a NixOS system, then true, otherwise false by default";
+      };
+      defaults = lib.mkOption {
+        description = mdDoc ''
+          Default configuration for that system type.
+        '';
+        type = types.functionTo types.unspecified;
+        default = _: {};
+      };
+      activationProgram = lib.mkOption {
+        description = mdDoc ''
+          Program to execute at activation time.
+        '';
+        type = types.path;
+      };
+    };
+  };
+  registryOptions = { lib, ... }: let
+    inherit (lib) types;
+    mdDoc = lib.mdDoc or lib.id;
+  in
+  {
+    options.registry = lib.mkOption {
+      description = mdDoc ''
+        A registry of all system types.
+      '';
+      type = types.attrsOf (types.submodule systemTypeOptions);
+    };
+  };
   # Hive-wide options
   metaOptions = { lib, ... }: let
     inherit (lib) types;

src/nix/host/generic.rs

@@ -0,0 +1,287 @@
+use std::collections::HashMap;
+use std::process::Stdio;
+
+use async_trait::async_trait;
+use serde::{Deserialize, Serialize};
+use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader, BufWriter};
+use tokio::process::{Child, ChildStdin, ChildStdout, Command};
+
+use super::{CopyDirection, CopyOptions, Host, RebootOptions};
+use crate::error::{ColmenaError, ColmenaResult};
+use crate::job::JobHandle;
+use crate::nix::{self, Key, Profile, StorePath, SystemTypeConfig};
+
+pub type TransportId = String;
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Transport {
+    id: TransportId,
+    long_name: String,
+    description: String,
+}
+
+pub type GoalId = String;
+
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Goal {
+    id: GoalId,
+    long_name: String,
+    description: String,
+}
+
+/// A request to the activation program
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub enum Request {
+    Connection {
+        connection_uri: String,
+    },
+
+    /// Copy closure to/from host
+    CopyClosure {
+        path: StorePath,
+        to_host: bool,
+        options: CopyOptions,
+    },
+
+    /// Deploys the profile to host
+    Deploy {
+        goal: GoalId,
+        toplevel: StorePath,
+        options: CopyOptions,
+    },
+
+    /// Realizes the derivation
+    Realize {
+        path: StorePath,
+        remote: bool,
+    },
+
+    /// Uploads keys to host
+    UploadKeys {
+        keys: HashMap<String, Key>,
+        require_ownership: bool,
+    },
+
+    Activate {
+        profile: StorePath,
+        goal: GoalId,
+    },
+
+    Reboot {
+        wait_for_boot: bool,
+    },
+}
+
+/// A response from the activation program
+#[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
+pub enum Response {
+    ConnectionFailed { error: String },
+    ConnectionSucceded { supported_goals: Vec<String> },
+    Progress { phase: String },
+    NewStorePath { store_path: StorePath },
+    Failed { error: String },
+    Unsupported,
+}
+
+#[derive(Debug)]
+pub struct ActivationCommand {
+    command: Child,
+    stdin: BufWriter<ChildStdin>,
+    stdout: BufReader<ChildStdout>,
+}
+
+#[derive(Debug)]
+pub struct GenericHost {
+    activation_program: ActivationCommand,
+    connection_uri: String,
+}
+
+#[async_trait]
+impl Host for GenericHost {
+    async fn copy_closure(
+        &mut self,
+        closure: &StorePath,
+        direction: CopyDirection,
+        options: CopyOptions,
+    ) -> ColmenaResult<()> {
+        self.call_default_handler(Request::CopyClosure {
+            path: closure.clone(),
+            to_host: direction == CopyDirection::ToRemote,
+            options,
+        })
+        .await
+    }
+
+    async fn realize_remote(&mut self, derivation: &StorePath) -> ColmenaResult<Vec<StorePath>> {
+        Ok(self
+            .call(
+                Request::Realize {
+                    path: derivation.clone(),
+                    remote: true
+                },
+                move |response, mut store_paths| {
+                    match response {
+                        Response::Progress { phase } => println!("{}", phase),
+                        Response::NewStorePath { store_path } => store_paths.push(store_path),
+                        _ => (),
+                    };
+                    store_paths
+                },
+                Vec::new(),
+            )
+            .await?)
+    }
+
+    async fn realize(&mut self, derivation: &StorePath) -> ColmenaResult<Vec<StorePath>> {
+        Ok(self
+            .call(
+                Request::Realize {
+                    path: derivation.clone(),
+                    remote: false
+                },
+                move |response, mut store_paths| {
+                    match response {
+                        Response::Progress { phase } => println!("{}", phase),
+                        Response::NewStorePath { store_path } => store_paths.push(store_path),
+                        _ => (),
+                    };
+                    store_paths
+                },
+                Vec::new(),
+            )
+            .await?)
+    }
+
+    fn set_job(&mut self, _: Option<JobHandle>) {}
+
+    async fn deploy(
+        &mut self,
+        profile: &Profile,
+        goal: nix::Goal,
+        copy_options: CopyOptions,
+    ) -> ColmenaResult<()> {
+        self.call_default_handler(Request::Deploy {
+            goal: goal.to_string(),
+            toplevel: profile.as_store_path().clone(),
+            options: copy_options,
+        })
+        .await
+    }
+
+    async fn upload_keys(
+        &mut self,
+        keys: &HashMap<String, Key>,
+        require_ownership: bool,
+    ) -> ColmenaResult<()> {
+        self.call_default_handler(Request::UploadKeys {
+            keys: keys.clone(),
+            require_ownership,
+        })
+        .await
+    }
+
+    async fn get_current_system_profile(&mut self) -> ColmenaResult<Profile> {
+        Err(ColmenaError::Unsupported)
+    }
+
+    async fn get_main_system_profile(&mut self) -> ColmenaResult<Profile> {
+        Err(ColmenaError::Unsupported)
+    }
+
+    async fn activate(&mut self, profile: &Profile, goal: nix::Goal) -> ColmenaResult<()> {
+        self.call_default_handler(Request::Activate {
+            profile: profile.as_store_path().clone(),
+            goal: goal.to_string(),
+        })
+        .await
+    }
+
+    async fn reboot(&mut self, options: RebootOptions) -> ColmenaResult<()> {
+        self.call_default_handler(Request::Reboot {
+            wait_for_boot: options.wait_for_boot,
+        })
+        .await
+    }
+}
+
+impl GenericHost {
+    pub fn new(system: &SystemTypeConfig, connection_uri: String) -> ColmenaResult<GenericHost> {
+        let mut command = Command::new(system.activation_program.as_path())
+            .stdin(Stdio::piped())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::inherit())
+            .spawn()?;
+
+        let stdin = BufWriter::new(command.stdin.take().unwrap());
+        let stdout = BufReader::new(command.stdout.take().unwrap());
+
+        let activation_program = ActivationCommand {
+            command,
+            stdin,
+            stdout,
+        };
+
+        Ok(Self {
+            activation_program,
+            connection_uri,
+        })
+    }
+
+    pub async fn connect(&mut self) -> ColmenaResult<()> {
+        self.call_default_handler(Request::Connection {
+            connection_uri: self.connection_uri.clone(),
+        })
+        .await
+    }
+
+    async fn call<F, T>(
+        &mut self,
+        request: Request,
+        handler: F,
+        initial_value: T,
+    ) -> ColmenaResult<T>
+    where
+        F: Fn(Response, T) -> T,
+    {
+        let json = serde_json::to_string(&request)
+            .map_err(|error| ColmenaError::InvalidActivationProgramJson { error })?;
+
+        log::trace!("giving to activation program stdin {}", json.as_str());
+
+        let stdin = &mut self.activation_program.stdin;
+        let stdout = &mut self.activation_program.stdout;
+
+        stdin.write_all(json.as_bytes()).await?;
+        stdin.write_all(b"\n").await?;
+        stdin.flush().await?;
+
+        let mut line = String::new();
+        let mut value = initial_value;
+
+        // We're reading JSONL, so we can read all the line and parse it
+        while stdout.read_line(&mut line).await.is_ok_and(|x| x != 0) {
+            if line == "\n" {
+                log::trace!("finished receiving responses from activation program");
+                break;
+            }
+            log::trace!("receiving from activation program:\n{}", line);
+            let response: Response = serde_json::from_str(line.as_str())
+                .map_err(|error| ColmenaError::InvalidActivationProgramJson { error })?;
+
+            match response {
+                Response::Progress { phase } => {
+                    log::info!("{phase}");
+                    break;
+                }
+                Response::Unsupported => return Err(ColmenaError::Unsupported),
+                _ => value = handler(response, value),
+            }
+        }
+
+        Ok(value)
+    }
+
+    async fn call_default_handler(&mut self, request: Request) -> ColmenaResult<()> {
+        self.call(request, |_, _| {}, ()).await
+    }
+}

src/nix/host/mod.rs

@@ -1,6 +1,7 @@
 use std::collections::HashMap;
 
 use async_trait::async_trait;
+use serde::{Deserialize, Serialize};
 
 use super::{Goal, Key, Profile, StorePath};
 use crate::error::{ColmenaError, ColmenaResult};
@@ -14,13 +15,16 @@ pub use local::Local;
 
 mod key_uploader;
 
-#[derive(Copy, Clone, Debug)]
+pub mod generic;
+pub use generic::GenericHost;
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub enum CopyDirection {
     ToRemote,
     FromRemote,
 }
 
-#[derive(Copy, Clone, Debug)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct CopyOptions {
     include_outputs: bool,
     use_substitutes: bool,
@@ -61,6 +65,18 @@ impl CopyOptions {
         self.gzip = val;
         self
     }
+
+    pub fn get_include_outputs(&self) -> bool {
+        self.include_outputs
+    }
+
+    pub fn get_use_substitutes(&self) -> bool {
+        self.use_substitutes
+    }
+
+    pub fn get_gzip(&self) -> bool {
+        self.gzip
+    }
 }
 
 impl Default for RebootOptions {

src/nix/mod.rs

@@ -10,8 +10,8 @@ use validator::{Validate, ValidationError as ValidationErrorType};
 use crate::error::{ColmenaError, ColmenaResult};
 
 pub mod host;
-use host::Ssh;
 pub use host::{CopyDirection, CopyOptions, Host, RebootOptions};
+use host::{GenericHost, Ssh};
 
 pub mod hive;
 pub use hive::{Hive, HivePath};
@@ -55,6 +55,9 @@ pub struct NodeName(#[serde(deserialize_with = "NodeName::deserialize")] String)
 
 #[derive(Debug, Clone, Validate, Deserialize)]
 pub struct NodeConfig {
+    #[serde(rename = "systemType")]
+    system_type: Option<String>,
+
     #[serde(rename = "targetHost")]
     target_host: Option<String>,
 
@@ -64,6 +67,9 @@ pub struct NodeConfig {
     #[serde(rename = "targetPort")]
     target_port: Option<u16>,
 
+    #[serde(rename = "connectionUri")]
+    connection_uri: String,
+
     #[serde(rename = "allowLocalDeployment")]
     allow_local_deployment: bool,
 
@@ -94,6 +100,21 @@ pub struct MetaConfig {
     pub machines_file: Option<String>,
 }
 
+#[derive(Debug, Clone, Validate, Deserialize)]
+pub struct SystemTypeConfig {
+    #[serde(rename = "supportsDeployment")]
+    pub supports_deployment: bool,
+
+    #[serde(rename = "activationProgram")]
+    pub activation_program: StorePath,
+}
+
+#[derive(Debug, Clone, Validate, Deserialize)]
+pub struct RegistryConfig {
+    #[serde(flatten)]
+    pub systems: HashMap<String, SystemTypeConfig>,
+}
+
 /// Nix CLI flags.
 #[derive(Debug, Clone, Default)]
 pub struct NixFlags {
@@ -193,6 +214,10 @@ impl NodeConfig {
             host
         })
     }
+
+    pub fn to_generic_host(&self, system_config: &SystemTypeConfig) -> ColmenaResult<GenericHost> {
+        GenericHost::new(system_config, self.connection_uri.clone())
+    }
 }
 
 impl NixFlags {