Rails: Rework service execution so `nix-copy-closure' deployments work better

These changes allow service restarts to pick up a new
environment (including the correct gemset) when restarted.

Also, make migrations its own service that other services need to wait
for.

modules/services/web/rails/build-path.sh

@@ -0,0 +1,52 @@
+#!/bin/bash
+
+################################################################################
+# Build a PATH variable given a nix-store path.
+set -e
+set -u
+
+################################################################################
+dirs=()
+
+################################################################################
+if [ $# -ne 1 ]; then
+  >&2 echo "ERROR: missing store path"
+  exit 1
+fi
+
+################################################################################
+function join() {
+  local sep=$1; shift
+  local IFS="$sep";
+  echo "$*";
+}
+
+################################################################################
+function maybe_add_dir() {
+  local path=$1
+
+  if [ -n "$path" ] && [ -d "$path/bin" ]; then
+    dirs+=( "$path/bin" )
+  fi
+}
+
+################################################################################
+function main() {
+  local path=$1
+  path=$(realpath "$path")
+
+  maybe_add_dir "$path"
+
+  for drv in $(nix-store --query --references "$path"); do
+    maybe_add_dir "$drv"
+  done
+
+  if [ "${#dirs[@]}" -gt 0 ]; then
+    echo "export PATH=$(join : "${dirs[@]}"):$PATH"
+  else
+    echo "export PATH=$PATH"
+  fi
+}
+
+################################################################################
+main "$1"

modules/services/web/rails/default.nix

@@ -72,7 +72,6 @@ let
       group = "rails-${app.name}";
       shell = "${pkgs.bash}/bin/bash";
       extraGroups = [ config.services.nginx.group ];
-      packages = funcs.appPath app;
     };
     groups."rails-${app.name}" = {};
   };

modules/services/web/rails/functions.nix

@@ -12,11 +12,6 @@ rec {
   # Path to where the app is actually installed:
   appLink = app: "${app.home}/package";
 
-  ##############################################################################
-  # Packages to put in the application's PATH.  FIXME:
-  # propagatedBuildInputs won't always be set.
-  appPath = app: [ app.package.rubyEnv ] ++ app.package.propagatedBuildInputs;
-
   ##############################################################################
   # All of the environment variables that a Rails app needs:
   appEnv = app: {

modules/services/web/rails/options.nix

@@ -86,6 +86,13 @@ let
         default = false;
         description = "Is this the main Rails process?";
       };
+
+      isMigration = mkOption {
+        internal = true;
+        type = types.bool;
+        default = false;
+        description = "Is this the migration service?";
+      };
     };
 
     config = {

modules/services/web/rails/profile.sh

@@ -1,4 +1,7 @@
 # Rails user shell profile.
+if [ -e "$HOME/.path" ]; then
+   . "$HOME/.path"
+fi
 
 if [ -e "$HOME/.env" ]; then
   . "$HOME/.env"

modules/services/web/rails/scripts.nix

@@ -8,6 +8,7 @@
     installPhase = ''
       mkdir -p $out/bin
       substituteAll ${./db-migrate.sh} $out/bin/db-migrate.sh
+      substituteAll ${./build-path.sh} $out/bin/build-path.sh
       find $out/bin -type f -exec chmod 555 '{}' ';'
     '';
 

modules/services/web/rails/systemd.nix

@@ -23,39 +23,56 @@ let
     name = "main";
     schedule = null;
     isMain = true;
+    isMigration = false;
 
     script = ''
       puma -e ${app.railsEnv} -p ${toString app.port}
     '';
   };
 
+  ##############################################################################
+  # The database migration service:
+  migrationService = app: {
+    name = "migrations";
+    schedule = null;
+    isMain = false;
+    isMigration = true;
+
+    script = ''
+      ${scripts.user}/bin/db-migrate.sh \
+        -r ${funcs.appLink app}/share/${app.name} \
+        -s ${app.home}/state
+    '';
+  };
+
   ##############################################################################
   # Generate a systemd service for a Ruby on Rails application:
   appService = app: service: {
     "rails-${app.name}-${service.name}" = {
       description = "${app.name} (Ruby on Rails) ${service.name}";
-      path = funcs.appPath app;
+      path = with pkgs; [ coreutils nix ];
       environment = funcs.appEnv app;
 
       # Only start this service if it isn't scheduled by a timer.
       partOf   = optional (service.schedule == null) "rails-${app.name}.target";
       wantedBy = optional (service.schedule == null) "rails-${app.name}.target";
 
-      wants =
-        plib.keyService app.database.passwordFile ++
-        plib.keyService app.sourcedFile ++
-        app.afterServices;
+      wants = plib.keyService app.database.passwordFile
+        ++ plib.keyService app.sourcedFile
+        ++ app.afterServices
+        ++ optional (!service.isMigration && app.database.migrate) "rails-${app.name}-migrations"
+        ++ optional (!service.isMain && !service.isMigration) "rails-${app.name}-main";
 
-      after =
-        [ "network.target" ] ++
-        optional localpg  "postgresql.service" ++
-        optional localpg  "pg-accounts.service" ++
-        optional (!service.isMain) "rails-${app.name}-main" ++
-        plib.keyService app.database.passwordFile ++
-        plib.keyService app.sourcedFile ++
-        app.afterServices;
+      after = [ "network.target" ]
+        ++ optional localpg  "postgresql.service"
+        ++ optional localpg  "postgres-account-manager.service"
+        ++ plib.keyService app.database.passwordFile
+        ++ plib.keyService app.sourcedFile
+        ++ app.afterServices
+        ++ optional (!service.isMigration && app.database.migrate) "rails-${app.name}-migrations"
+        ++ optional (!service.isMain && !service.isMigration) "rails-${app.name}-main";
 
-      preStart = optionalString service.isMain ''
+      preStart = optionalString (service.isMain || service.isMigration) ''
         # Link the package into the application's home directory:
         if [ ! -e "${funcs.appLink app}" ] || [ "${toString app.deployedExternally}" -ne 1 ]; then
           ln -nfs "${app.package}" "${funcs.appLink app}"
@@ -73,6 +90,7 @@ let
         mkdir -p ${app.home}/home
         ln -nfs ${funcs.appLink app}/share/${app.name} ${app.home}/home/app
         ln -nfs ${plib.attrsToShellExports "rails-${app.name}-env" (funcs.appEnv app)} ${app.home}/home/.env
+        echo 'eval $(${scripts.user}/bin/build-path.sh "${funcs.appLink app}")' > ${app.home}/home/.path
         cp ${./profile.sh} ${app.home}/home/.profile
         chmod 0700 ${app.home}/home/.profile
 
@@ -85,25 +103,19 @@ let
         chown -R rails-${app.name}:rails-${app.name} ${app.home}
         chmod go+rx $(dirname "${app.home}") "${app.home}"
         chmod u+w ${app.home}/db/schema.rb
-
-      '' + optionalString (service.isMain && app.database.migrate) ''
-        # Migrate the database:
-        ${pkgs.sudo}/bin/sudo --user=rails-${app.name} --login \
-          ${scripts.user}/bin/db-migrate.sh \
-            -r ${funcs.appLink app}/share/${app.name} \
-            -s ${app.home}/state
       '';
 
       script = ''
         ${optionalString (app.sourcedFile != null) ". ${app.home}/state/sourcedFile.sh"}
+        eval $(${scripts.user}/bin/build-path.sh "${funcs.appLink app}")
         ${service.script}
       '';
 
       serviceConfig = {
         WorkingDirectory = "-${funcs.appLink app}/share/${app.name}";
-        Restart = "on-failure";
+        Type = if service.isMigration then "oneshot" else "simple";
+        Restart = if service.isMigration then "no" else "on-failure";
         TimeoutSec = "infinity"; # FIXME: what's a reasonable amount of time?
-        Type = "simple";
         PermissionsStartOnly = true;
         User = "rails-${app.name}";
         Group = "rails-${app.name}";
@@ -128,7 +140,9 @@ let
   # systemd services.
   appServices = app:
     foldr (service: set: recursiveUpdate set (appService app service)) {}
-          ( [(mainService app)] ++ attrValues app.services );
+      ( singleton (mainService app)
+        ++ optional app.database.migrate (migrationService app)
+        ++ attrValues app.services );
 
   ##############################################################################
   # Collect all services and turn them into systemd timers: