Accessing Alfred Jobs via the Web

In this document:

• Introduction
• Configuring for HTTP Access
• Connecting to the Maitre-d

   

• Example Alfred Status Pages
  • List of Active Dispatchers
  • Jobs on a Specific Dispatcher
  • The Task Hierarchy
  • Details of a Particular Task

   

• Wrangler Mode
• Limitations of the Web Interface

Introduction

The maitre-d functions as the Alfred "homepage" and so there must be an Alfred running in -maitre_d mode for the HTTP interface to work.

It is important to understand that this mode is a stand-alone feature of Alfred. There is no requirement to install scripts or links into your site's standard HTTP server directories. Alfred listens for HTTP connections on a specific TCP port and responds directly to the requesting browser.

Since there is support for previewing rendered frames, which involves a limited form of file transfer, it is also important to review the security settings in the alfred.ini file.

Configuring for HTTP Access

	set alfConfig(maitredHost) {snappy.busy.com}
	set alfConfig(maitredPort) 9000
	set alfConfig(allowHTTP) 1

A more general approach, which also supports fall-back maitre-ds, is to install the provided maitre-d.cgi script, which can automatically redirect users to the appropriate maitre-d and TCP port. Note that this option does require integration with the site's standard HTTP server. After the script has been installed, the Alfred URL would be:

Connecting to the Maitre-d

Note that access to each dispatcher is password protected. Individual users must enable access to their dispatcher using the Session->Preferences->Web Access properties dialog from the regular Alfred monitor.

In order to support the broadest range of web browsers, Alfred uses a fairly simple format for its status information. It does make use of HTML tables for structured layout, and HTML forms for a few situations in which user input is required. See the limitations section for more details on browser requirements.

A few example status pages are included below to illustrate the interface.

 All Dispatchers on the Network

Current Alfred Dispatchers Wed, 08 Apr 1998 13:45:10 Jobs Dispatchers ----------- Waiting ------- Active ------ Done ----- dana@drizzle 0 1 2 david@grotto 2 1 0 ned@area51 0 1 0 Errors bones@lluvia 0 0 3

Jobs on a Specific Dispatcher

Clicking on the job title will cause Alfred to generate an HTML version of the detailed task tree for entire job. Alternatively, if a job is active, the word Active will also be highlighted as a link, clicking it will put the dispatcher into a special mode in which it constantly generates status updates limited to the active portions of the job tree.

 The Task Hierarchy

In this job status view, clicking on the short "___" link between the task title and its status brings up a page showing the current task "guts" and any task output logs. A link formatted as "_i_" indicates that there has been output.

Finished frames can be downloaded to the browser (for preview, etc). If there are frames available they will be indicated by "[image]" links in the job status listing (above). To enable this feature the httpImgRoot parameter in the alfred.ini file must be set and the job script must specify a special chaser command for the final frame tasks.

Details of a Particular Task

Command Internals

Commands:
 [Active]: netrender -f -Progress %H rib/preview.0003.rib
   [keys]: pixarNrm
   [tags]: prman
  [hosts]: cerberus
  [start]: Wed Apr 08 13:37:42 1998
    [end]: (still active, pid=18150)

Clean-up:
   (none)

Chaser Cmd:
   sho rmanpix/preview.0003.tif

Command Output

S01001 cannot load shader "alien-marble".  (WARNING)

Wrangler Mode

See the configuration discussion for details on enabling wrangler mode at your site.

To enter wrangler mode:

• Point a web browser at the maitre-d URL.
• Click on the Alfred icon to go to the "About..." page.

  

   

• A login form will be displayed, enter your name and the wrangler password.
• The maitre-d will respond with a special version of the current dispatcher listing which contains expanded job information. The wrangler will also be able to browse any user's jobs in detail.
• Note: the maitre-d generates an encoded http "cookie" as part of the wrangler login process, it is used to authenticate subsequent requests to the maitre-d and dispatchers. The cookie remains valid for a limited time (usually a day); it is not saved when the browser exits.
• To end wrangler mode, return to the "About..." page and press the "Leave" button (which unsets the cookie). The wrangler session also ends if an administrator uses "alfred -wpasswd" to change the current password.

Limitations of the Web Interface

• The web browser UI supports a limited subset of the functions available via the regular alfred monitor. Release 3.0 provides a simple mechanism for reordering job queues and changing individual job priority. However there is currently no web-based mechanism for modifying crew and server definitions (very experienced administrators might be able to accomplish emergency changes by logging in to the maitre-d host and editing the schedule file directly, this should be a last resort though).

   

• The HTTP support requires a running maitre-d which manages the initial browser connections and lists all running dispatchers on the network. See the alfred.ini file for details on specifying the maitre-d's URL.

   

• The alfred HTTP support assumes a fairly up-to-date browser (Netscape 2.0, MSIE 3.0, or better). Specifically, the HTML is level 2.0 (includes tables and forms); and it relies on proper handling of the no-cache directive: that is, the interface assumes that reloading an alfred-generated page will retrieve fresh job status, rather than continuously redisplaying old (cached) status.

   

• The server-push update mechanism is used only for Netscape clients, client-pull otherwise. These are mechanisms whereby the HTML for the status page is either refreshed periodically by alfred (server-push), or by the browser automatically "pushing the reload button" itself (client-pull). Automatic updates of active jobs can be interrupted by going to another page (the "full" job mode, for example), or by pushing the browser "Stop" button in server-push mode.

   

• Since the HTTP mode is self-contained, alfred does not need, look for, or abide by, any other web server configurations or restrictions which may be in force at a site.

   

• The alfred.ini file controls whether alfred HTTP connections are allowed at all, for the site. If connections are globally enabled, then users can connect to dispatchers (via the maitre-d) after "logging in" from their browser. There is only very simple security on HTTP connections. Since it is difficult (by design) to authenticate the owner of a browser, alfred uses the "Basic" WWW authentication mechanism to prompt connecting web users for an alfred password. The password must initially be set using the regular alfred UI ("Web Password" on the Preferences dialog). The encrypted password is stored in ~/.pixarPrefs/alfred.prefs, although an encoded but essentially clear-text version is transmitted over the network during the initial browser connection. If the encrypted user password (in the prefs file) is the empty string "{}" then connections are not allowed; if the encrypted password is asterisk "*" then password checking is disabled, this feature should be used with caution, i.e. on trusted networks behind a firewall.

  The alfred.ini file also defines the location of the wrangler-mode password file. The initial wrangler authentication (with the maitre-d) is done using a one-time HTML form (about as secure as telnet or ftp), however subsequent per-dispatcher wrangler authentication is done using a fairly secure, encrypted HTTP cookie, which is generated by the maitre-d. This avoids requiring separate logins for each dispatcher or sending insecure Basic authentication strings with each wrangler transaction.