Add systemd support

This adds a basic service file for celeryd and associated bits to
install it on Xenial and beyond.

Change-Id: I58ab956832acabf9e5af5f815e37ed1eb365a649

manifests/site/celeryd.pp

@@ -3,20 +3,51 @@
 class askbot::site::celeryd (
   $site_root,
 ) {
-  file { '/etc/init/askbot-celeryd.conf':
-    ensure  => present,
-    owner   => 'root',
-    group   => 'root',
-    mode    => '0644',
-    content => template('askbot/celeryd.upstart.conf.erb'),
-    require => Exec['askbot-migrate'],
-  }
 
-  service { 'askbot-celeryd':
-    ensure     => running,
-    enable     => true,
-    hasrestart => true,
-    require    => File['/etc/init/askbot-celeryd.conf'],
-    subscribe  => [ Exec['askbot-migrate'], File["${site_root}/config/settings.py"] ]
+  if ($::operatingsystem == 'Ubuntu') and versioncmp($::operatingsystemrelease, '16.04') >= 0 {
+
+    file { '/etc/systemd/system/askbot-celeryd.service':
+      ensure  => present,
+      owner   => 'root',
+      group   => 'root',
+      content => template('askbot/askbot-celeryd.service.erb'),
+      require => Exec['askbot-migrate'],
+    }
+
+    service { 'askbot-celeryd':
+      ensure     => running,
+      enable     => true,
+      hasrestart => false,
+      require    => File['/etc/systemd/system/askbot-celeryd.service'],
+    }
+
+    # This is a hack to make sure that systemd is aware of the new service
+    # before we attempt to start it.
+    exec { 'celeryd-systemd-daemon-reload':
+      command     => '/bin/systemctl daemon-reload',
+      before      => Service['askbot-celeryd'],
+      subscribe   => File['/etc/systemd/system/askbot-celeryd.service'],
+      refreshonly => true,
+    }
+
+  } else {
+
+    file { '/etc/init/askbot-celeryd.conf':
+      ensure  => present,
+      owner   => 'root',
+      group   => 'root',
+      mode    => '0644',
+      content => template('askbot/celeryd.upstart.conf.erb'),
+      require => Exec['askbot-migrate'],
+    }
+
+    service { 'askbot-celeryd':
+      ensure     => running,
+      enable     => true,
+      hasrestart => true,
+      require    => File['/etc/init/askbot-celeryd.conf'],
+      subscribe  => [ Exec['askbot-migrate'], File["${site_root}/config/settings.py"] ]
+    }
+
   }
 }

templates/askbot-celeryd.service.erb

@@ -0,0 +1,14 @@
+[Unit]
+Description=Celery Service
+After=network.target
+
+[Service]
+Type=simple
+User=www-data
+Group=www-data
+WorkingDirectory=/srv/askbot-site/config
+ExecStart=/usr/askbot-env/bin/python manage.py celeryd -c 5 --maxtasksperchild=1000 --time-limit=30
+ExecStop=/bin/kill -INT $MAINPID
+
+[Install]
+WantedBy=multi-user.target