factor out ssh deployment to make for reusable invocation

deployment/check/common/data-model-options.nix

@@ -3,13 +3,23 @@
   ...
 }:
 let
-  inherit (lib) types;
+  inherit (lib) mkOption types;
 in
 {
   options = {
-    host = lib.mkOption {
+    host = mkOption {
       type = types.str;
       description = "name of the host to deploy to";
     };
+    targetSystem = mkOption {
+      type = types.str;
+      description = "name of the host to deploy to";
+    };
+    sshOpts = mkOption {
+      description = "Extra SSH options (`-o`) to use.";
+      type = types.listOf types.str;
+      default = [ ];
+      example = "ConnectTimeout=60";
+    };
   };
 }

deployment/check/common/data-model.nix

@@ -1,17 +1,29 @@
 {
   config,
   system,
-  inputs ? (import ../../../default.nix { }).inputs,
+  inputs ? (import ../../../default.nix { }).inputs, # XXX can't be serialized
   sources ? import ../../../npins,
   ...
-}:
+}@args:
 
 let
+  # having this module's location (`self`) and (serializable) `args`, we know
+  # enough to make it re-call itself to extract different info elsewhere later.
+  # we use this to make a deployment script using the desired nixos config,
+  # which would otherwise not be serializable, while nix also makes it hard to
+  # produce its derivation to pass thru without a `nix-instantiate` call,
+  # which in turn would need to be passed the (unserializable) nixos config.
+  self = "deployment/check/common/data-model.nix";
   inherit (sources) nixpkgs;
   pkgs = import nixpkgs { inherit system; };
   inherit (pkgs) lib;
   deployment-config = config;
-  inherit (deployment-config) nodeName;
+  inherit (deployment-config)
+    nodeName
+    pathToRoot
+    targetSystem
+    sshOpts
+    ;
   inherit (lib) mkOption types;
   eval =
     module:
@@ -124,15 +136,25 @@ let
           {
             single-nixos-vm-ssh = environment: {
               resources."operator-environment".login-shell.username = "operator";
-              implementation = requests: {
+              implementation =
-                input = requests;
+                {
+                  required-resources,
+                  deployment-name,
+                }:
+                {
+                  input = required-resources;
                   output.ssh-host = {
-                  nixos-configuration = mkNixosConfiguration environment requests;
+                    nixos-configuration = mkNixosConfiguration environment required-resources;
+                    system = targetSystem;
                     ssh = {
                       username = "root";
                       host = nodeName;
                       key-file = null;
+                      inherit sshOpts;
                     };
+                    module = self;
+                    inherit args deployment-name;
+                    root-path = pathToRoot;
                   };
                 };
             };
@@ -175,7 +197,10 @@ let
           in
           mkOption {
             type = env.resource-mapping.output-type;
-            default = env.deployment config."example-configuration";
+            default = env.deployment {
+              deployment-name = "ssh-deployment";
+              configuration = config."example-configuration";
+            };
           };
         "nixops4-deployment" =
           let
@@ -183,7 +208,10 @@ let
           in
           mkOption {
             type = env.resource-mapping.output-type;
-            default = env.deployment config."example-configuration";
+            default = env.deployment {
+              deployment-name = "nixops4-deployment";
+              configuration = config."example-configuration";
+            };
           };
       };
     }

deployment/check/common/sharedOptions.nix

@@ -32,11 +32,10 @@ in
     };
 
     pathFromRoot = mkOption {
-      type = types.path;
+      type = types.str;
       description = ''
         Path from the root of the repository to the working directory.
       '';
-      apply = x: lib.path.removePrefix config.pathToRoot x;
     };
 
     pathToCwd = mkOption {

deployment/check/data-model-ssh/nixosTest.nix

@@ -1,30 +1,26 @@
 {
   lib,
-  config,
   pkgs,
-  inputs,
   ...
 }:
 let
   inherit (import ./constants.nix) pathToRoot pathFromRoot;
   inherit (pkgs) system;
-  escapedJson = v: lib.replaceStrings [ "\"" ] [ "\\\\\"" ] (lib.strings.toJSON v);
   deployment-config = {
     inherit pathToRoot pathFromRoot;
-    inherit (config) enableAcme;
-    acmeNodeIP = if config.enableAcme then config.nodes.acme.networking.primaryIPAddress else null;
     nodeName = "ssh";
+    targetSystem = system;
+    sshOpts = [
+      "ConnectTimeout=1"
+      "ServerAliveInterval=1"
+    ];
   };
-  inherit
+  deployment =
-    ((import ../common/data-model.nix {
+    (import ../common/data-model.nix {
-      inherit system inputs;
+      inherit system;
       config = deployment-config;
-    })."ssh-deployment".ssh-host.ssh
+      # opt not to pass `inputs`, as we could only pass serializable arguments through to its self-call
-    )
+    })."ssh-deployment".ssh-host;
-    host
-    username
-    key-file
-    ;
 in
 {
   _class = "nixosTest";
@@ -36,6 +32,10 @@ in
   sourceFileset = lib.fileset.unions [
     ../../data-model.nix
     ../../function.nix
+    ../../nixos.nix
+    ../../run/ssh-single-host/run.sh
+    ../../../npins/default.nix
+    ../../../npins/sources.json
     ../common/data-model.nix
     ../common/data-model-options.nix
     ./constants.nix
@@ -63,46 +63,7 @@ in
 
     with subtest("Run the deployment"):
       deployer.succeed("""
-        set -euo pipefail
+        ${deployment.run}
-
-        # INSTANTIATE
-        command=(nix-instantiate --show-trace --expr '
-          let
-            system = "${pkgs.system}"; # FIXME: what system are we deploying to?
-          in
-          import ${pathToRoot}/deployment/nixos.nix {
-            inherit system;
-            configuration = (
-              import ${pathToRoot}/deployment/check/common/data-model.nix {
-                inherit system;
-                config = builtins.fromJSON "${escapedJson deployment-config}";
-              }
-            )."ssh-deployment".ssh-host.nixos-configuration;
-          }
-        ')
-        # DEPLOY
-        host="${lib.defaultTo "root" username}@${host}"
-        sshOpts=(
-          ${if key-file == null then "" else "-i ${key-file}"}
-          -o StrictHostKeyChecking=no
-          -o "ConnectTimeout=1"
-          -o "ServerAliveInterval=1"
-        )
-        # instantiate the config in /nix/store
-        "''${command[@]}" --show-trace -A out_path
-        # get the realized derivation to deploy
-        outPath=$(nix-store --realize "$("''${command[@]}" --show-trace --eval --strict --json | jq -r '.drv_path')")
-        # deploy the config by nix-copy-closure
-        NIX_SSHOPTS="''${sshOpts[*]}" nix-copy-closure --to "$host" "$outPath" --gzip --use-substitutes
-        # switch the remote host to the config
-        output=$(ssh "''${sshOpts[@]}" "$host" "nix-env --profile /nix/var/nix/profiles/system --set $outPath; nohup $outPath/bin/switch-to-configuration switch &" 2>&1) || echo "status code: $?"
-        echo "output: $output"
-        if [[ $output != *"Timeout, server ssh not responding"* ]]; then
-          echo "non-timeout error: $output"
-          exit 1
-        else
-          exit 0
-        fi
       """)
       ssh.wait_for_unit("multi-user.target")
       ssh.succeed("su - operator -c hello 1>&2")

deployment/data-model.nix

@@ -18,6 +18,16 @@ let
     str
     submodule
     ;
+  toBash =
+    v:
+    lib.replaceStrings [ "\"" ] [ "\\\\\"" ] (
+      if lib.isPath v || builtins.isNull v then
+        toString v
+      else if lib.isString v then
+        v
+      else
+        lib.strings.toJSON v
+    );
 
   functionType = submodule ./function.nix;
   application-resources = submodule {
@@ -65,18 +75,85 @@ let
           type = nullOr str;
           example = "/root/.ssh/id_ed25519";
         };
+        sshOpts = mkOption {
+          description = "Extra SSH options (`-o`) to use.";
+          type = types.listOf str;
+          default = [ ];
+          example = "ConnectTimeout=60";
+        };
       };
     };
   };
   deployment-type = attrTag {
     ssh-host = mkOption {
       description = "A deployment by SSH to update a single existing NixOS host.";
-      type = submodule {
+      type = submodule (ssh-host: {
         options = {
+          system = mkOption {
+            description = "The architecture of the system to deploy to.";
+            type = types.str;
+          };
           inherit nixos-configuration;
           ssh = host-ssh;
+          module = mkOption {
+            description = "The module to call to obtain the NixOS configuration from.";
+            type = types.str;
+          };
+          args = mkOption {
+            description = "The arguments with which to call the module to obtain the NixOS configuration.";
+            type = types.attrs;
+          };
+          deployment-name = mkOption {
+            description = "The name of the deployment for which to obtain the NixOS configuration.";
+            type = types.str;
+          };
+          root-path = mkOption {
+            description = "The path to the root of the repository.";
+            type = types.path;
+          };
+          run = mkOption {
+            type = types.str;
+            # error: The option `ssh-deployment.ssh-host.run' is read-only, but it's set multiple times.
+            # readOnly = true;
+            default =
+              let
+                inherit (ssh-host.config)
+                  system
+                  ssh
+                  module
+                  args
+                  deployment-name
+                  root-path
+                  ;
+                inherit (ssh)
+                  host
+                  username
+                  key-file
+                  sshOpts
+                  ;
+                environment = {
+                  key_file = key-file;
+                  deployment_name = deployment-name;
+                  root_path = root-path;
+                  ssh_opts = sshOpts;
+                  inherit
+                    system
+                    host
+                    username
+                    module
+                    args
+                    ;
+                  deployment_type = "ssh-host";
+                };
+              in
+              ''
+                env ${
+                  toString (lib.mapAttrsToList (k: v: "${k}=\"${toBash v}\"") environment)
+                } bash ./deployment/run/ssh-single-host/run.sh
+              '';
           };
         };
+      });
     };
     nixops4 = mkOption {
       description = "A NixOps4 NixOS deployment. For an example, see https://github.com/nixops4/nixops4-nixos/blob/main/example/deployment.nix.";

deployment/run/ssh-single-host/run.sh

@@ -0,0 +1,49 @@
+#! /usr/bin/env bash
+set -xeuo pipefail
+declare username host system module args deployment_name deployment_type key_file root_path ssh_opts
+IFS=" " read -r -a ssh_opts <<< "$( (echo "$ssh_opts" | jq -r '@sh') | tr -d \'\")"
+
+# DEPLOY
+sshOpts=(
+  -o BatchMode=yes
+  -o StrictHostKeyChecking=no
+)
+for ssh_opt in "${ssh_opts[@]}"; do
+  sshOpts+=(
+    -o "$ssh_opt"
+  )
+done
+if [[ -n "$key_file" ]]; then
+  sshOpts+=(
+    -i "$key_file"
+  )
+fi
+destination="$username@$host"
+
+command=(nix-instantiate --show-trace --expr "
+  import $root_path/deployment/nixos.nix {
+    system = \"$system\";
+    configuration = (import \"$root_path/$module\" (builtins.fromJSON ''$args'')).$deployment_name.$deployment_type.nixos-configuration;
+  }
+")
+
+# INSTANTIATE
+# instantiate the config in /nix/store
+"${command[@]}" -A out_path
+
+# get the realized derivation to deploy
+outPath=$(nix-store --realize "$("${command[@]}" --show-trace --eval --strict --json | jq -r '.drv_path')")
+# deploy the config by nix-copy-closure
+NIX_SSHOPTS="${sshOpts[*]}" nix-copy-closure --to "$destination" "$outPath" --gzip --use-substitutes
+# switch the remote host to the config
+# shellcheck disable=SC2029
+ssh "${sshOpts[@]}" "$destination" "nix-env --profile /nix/var/nix/profiles/system --set $outPath"
+# shellcheck disable=SC2029
+output=$(ssh "${sshOpts[@]}" "$destination" "nohup $outPath/bin/switch-to-configuration switch &" 2>&1) || echo "status code: $?"
+echo "output: $output"
+if [[ $output != *"Timeout, server $host not responding"* ]]; then
+  echo "non-timeout error: $output"
+  exit 1
+else
+  exit 0
+fi