Version 3 (modified by pjotr2007, 11 years ago)

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Aynchronous Communications (Pjotr)

AC has many possible implementations and the main danger is to overcomplicate a solution (trying to facilitate all wishes and real user requirements).

Typical use case

Typically a user creates a webservice (HTTP) and needs a way of executing a job that may take longer than the time a browser times out (think of BLAST). Potentially the job can take a month to run and both the client, server and network may be occasionaly down. Finally the user gets the output from the job - with output on success, error on failure.

The webservice author will want a clean API which allows job submission and passing the feedback mechanism in the simplest way possible.

Minimal Specification

A only job of the AC is to provide the messaging service between client and job.

What it should do:

  • Receive info from web-service (jobreceiver)
  • Start remote job on cluster (jobmonitor)
  • Pipe input data to job (jobmonitor)
  • Monitor job status (on failure perhaps restart)
  • Get output (jobmonitor)
  • Push output to client (jobsender)

What it should *not* do:

  • Authentication/authorisation (is responsibility of the webservice)
  • Filtering of data (modifying the stream) is responsibility of webservice)
  • Job control (handled by cluster tools)

In its minimalistic fashion it does not even handle status reports (i.e. percentage of job executed).

API

  • jobreceiver may be able to receive jobs through SOAP, a pipe, or mail
  • jobmonitor may be able to give updates on percentage executed (SOAP, RPC)
  • jobsender may be able to return results through SOAP, pipe or mail

Notes

  • The jobmonitor has to be stateful as the server or node running the job may go down
  • The jobmonitor is a little complicated as it has to allow for multiple types of (cluster) management tools
  • Piping is an incredibly useful mechanism. The complication with webservices is the asynchronous nature (while the web protocol tends to by synchronous) - inspiration could be  modglue (a Plan9-inspired extension of the Unix pipe concept). What I would like to do is:

acjob -t pipe "dbfetch URI:gb -t fasta|clustalw"|phyloanalyse > tree.ph

where dbfetch and clustalw run on the cluster and phyloanalyse locally - just as an example. Obviously with pipes you expect the client to keep running uninterrupted. The AC version could be (simplistically):

acjob -t email me@… "dbfetch URI:gb -t fasta|clustalw" cat email|phyloanalyse > tree.ph

or:

acjob -t poll "dbfetch URI:gb -t fasta|clustalw"|acpoll -i 180|phyloanalyse > tree.ph

where acpoll polls the jobmonitor every 3 minutes for results (SOAP is one option). acpoll would also allow a later 'progress monitor' implementation.

The nice thing about these piping mechanisms is that it shows clearly the minimal requirement for an implementation. Things like distributing services (multiple pipes) get resolved by the tools that are called by acmonitor. I.e. it is not a functionality for the jobmonitor itself.

Pjotr Prins