diff --git a/src/applications/config/option/PhabricatorAccessLogConfigOptions.php b/src/applications/config/option/PhabricatorAccessLogConfigOptions.php
index 6183f9936f..9ae60825ea 100644
--- a/src/applications/config/option/PhabricatorAccessLogConfigOptions.php
+++ b/src/applications/config/option/PhabricatorAccessLogConfigOptions.php
@@ -1,135 +1,136 @@
 <?php
 
 final class PhabricatorAccessLogConfigOptions
   extends PhabricatorApplicationConfigOptions {
 
   public function getName() {
     return pht('Access Logs');
   }
 
   public function getDescription() {
     return pht('Configure the access logs, which log HTTP/SSH requests.');
   }
 
   public function getIcon() {
     return 'fa-list';
   }
 
   public function getGroup() {
     return 'core';
   }
 
   public function getOptions() {
     $common_map = array(
       'C' => pht('The controller or workflow which handled the request.'),
       'c' => pht('The HTTP response code or process exit code.'),
       'D' => pht('The request date.'),
       'e' => pht('Epoch timestamp.'),
       'h' => pht("The webserver's host name."),
       'p' => pht('The PID of the server process.'),
       'r' => pht('The remote IP.'),
       'T' => pht('The request duration, in microseconds.'),
       'U' => pht('The request path, or request target.'),
       'm' => pht('For conduit, the Conduit method which was invoked.'),
       'u' => pht('The logged-in username, if one is logged in.'),
       'P' => pht('The logged-in user PHID, if one is logged in.'),
       'i' => pht('Request input, in bytes.'),
       'o' => pht('Request output, in bytes.'),
+      'I' => pht('Cluster instance name, if configured.'),
     );
 
     $http_map = $common_map + array(
       'R' => pht('The HTTP referrer.'),
       'M' => pht('The HTTP method.'),
     );
 
     $ssh_map = $common_map + array(
       's' => pht('The system user.'),
       'S' => pht('The system sudo user.'),
       'k' => pht('ID of the SSH key used to authenticate the request.'),
     );
 
     $http_desc = pht(
       'Format for the HTTP access log. Use `%s` to set the path. '.
       'Available variables are:',
       'log.access.path');
     $http_desc .= "\n\n";
     $http_desc .= $this->renderMapHelp($http_map);
 
     $ssh_desc = pht(
       'Format for the SSH access log. Use %s to set the path. '.
       'Available variables are:',
       'log.ssh.path');
     $ssh_desc .= "\n\n";
     $ssh_desc .= $this->renderMapHelp($ssh_map);
 
     return array(
       $this->newOption('log.access.path', 'string', null)
         ->setLocked(true)
         ->setSummary(pht('Access log location.'))
         ->setDescription(
           pht(
             "To enable the Phabricator access log, specify a path. The ".
             "Phabricator access than normal HTTP access logs (for instance, ".
             "it can show logged-in users, controllers, and other application ".
             "data).\n\n".
             "If not set, no log will be written."))
         ->addExample(
           null,
           pht('Disable access log.'))
         ->addExample(
           '/var/log/phabricator/access.log',
           pht('Write access log here.')),
       $this->newOption(
         'log.access.format',
         // NOTE: This is 'wild' intead of 'string' so "\t" and such can be
         // specified.
         'wild',
         "[%D]\t%p\t%h\t%r\t%u\t%C\t%m\t%U\t%R\t%c\t%T")
         ->setLocked(true)
         ->setSummary(pht('Access log format.'))
         ->setDescription($http_desc),
       $this->newOption('log.ssh.path', 'string', null)
         ->setLocked(true)
         ->setSummary(pht('SSH log location.'))
         ->setDescription(
           pht(
             "To enable the Phabricator SSH log, specify a path. The ".
             "access log can provide more detailed information about SSH ".
             "access than a normal SSH log (for instance, it can show ".
             "logged-in users, commands, and other application data).\n\n".
             "If not set, no log will be written."))
         ->addExample(
           null,
           pht('Disable SSH log.'))
         ->addExample(
           '/var/log/phabricator/ssh.log',
           pht('Write SSH log here.')),
       $this->newOption(
         'log.ssh.format',
         'wild',
         "[%D]\t%p\t%h\t%r\t%s\t%S\t%u\t%C\t%U\t%c\t%T\t%i\t%o")
         ->setLocked(true)
         ->setSummary(pht('SSH log format.'))
         ->setDescription($ssh_desc),
     );
   }
 
   private function renderMapHelp(array $map) {
     $desc = '';
     foreach ($map as $key => $kdesc) {
       $desc .= "  - `%".$key."` ".$kdesc."\n";
     }
     $desc .= "\n";
     $desc .= pht(
       "If a variable isn't available (for example, %%m appears in the file ".
       "format but the request is not a Conduit request), it will be rendered ".
       "as '-'");
     $desc .= "\n\n";
     $desc .= pht(
       "Note that the default format is subject to change in the future, so ".
       "if you rely on the log's format, specify it explicitly.");
 
     return $desc;
   }
 
 }
diff --git a/src/infrastructure/log/PhabricatorAccessLog.php b/src/infrastructure/log/PhabricatorAccessLog.php
index d3d9979aac..2ffa0577a8 100644
--- a/src/infrastructure/log/PhabricatorAccessLog.php
+++ b/src/infrastructure/log/PhabricatorAccessLog.php
@@ -1,41 +1,42 @@
 <?php
 
 final class PhabricatorAccessLog extends Phobject {
 
   private static $log;
 
   public static function init() {
     // NOTE: This currently has no effect, but some day we may reuse PHP
     // interpreters to run multiple requests. If we do, it has the effect of
     // throwing away the old log.
     self::$log = null;
   }
 
   public static function getLog() {
     if (!self::$log) {
       $path = PhabricatorEnv::getEnvConfig('log.access.path');
       $format = PhabricatorEnv::getEnvConfig('log.access.format');
       $format = nonempty(
         $format,
         "[%D]\t%p\t%h\t%r\t%u\t%C\t%m\t%U\t%R\t%c\t%T");
 
       // NOTE: Path may be null. We still create the log, it just won't write
       // anywhere.
 
       $log = id(new PhutilDeferredLog($path, $format))
         ->setFailQuietly(true)
         ->setData(
           array(
             'D' => date('r'),
             'h' => php_uname('n'),
             'p' => getmypid(),
             'e' => time(),
+            'I' => PhabricatorEnv::getEnvConfig('cluster.instance'),
           ));
 
       self::$log = $log;
     }
 
     return self::$log;
   }
 
 }
diff --git a/src/infrastructure/log/PhabricatorSSHLog.php b/src/infrastructure/log/PhabricatorSSHLog.php
index 9f9f75b41b..de4c270f72 100644
--- a/src/infrastructure/log/PhabricatorSSHLog.php
+++ b/src/infrastructure/log/PhabricatorSSHLog.php
@@ -1,52 +1,53 @@
 <?php
 
 final class PhabricatorSSHLog extends Phobject {
 
   private static $log;
 
   public static function getLog() {
     if (!self::$log) {
       $path = PhabricatorEnv::getEnvConfig('log.ssh.path');
       $format = PhabricatorEnv::getEnvConfig('log.ssh.format');
       $format = nonempty(
         $format,
         "[%D]\t%p\t%h\t%r\t%s\t%S\t%u\t%C\t%U\t%c\t%T\t%i\t%o");
 
       // NOTE: Path may be null. We still create the log, it just won't write
       // anywhere.
 
       $data = array(
         'D' => date('r'),
         'h' => php_uname('n'),
         'p' => getmypid(),
         'e' => time(),
+        'I' => PhabricatorEnv::getEnvConfig('cluster.instance'),
       );
 
       $sudo_user = PhabricatorEnv::getEnvConfig('phd.user');
       if (strlen($sudo_user)) {
         $data['S'] = $sudo_user;
       }
 
       if (function_exists('posix_geteuid')) {
         $system_uid = posix_geteuid();
         $system_info = posix_getpwuid($system_uid);
         $data['s'] = idx($system_info, 'name');
       }
 
       $client = getenv('SSH_CLIENT');
       if (strlen($client)) {
         $remote_address = head(explode(' ', $client));
         $data['r'] = $remote_address;
       }
 
       $log = id(new PhutilDeferredLog($path, $format))
         ->setFailQuietly(true)
         ->setData($data);
 
       self::$log = $log;
     }
 
     return self::$log;
   }
 
 }