Version 6 (modified by pjotr2007, 10 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

Amazon Cluster Cloud (EC2)

We should take a cue from Amazon's example - as their services for cluster computing and storage prove extremely useful and popular. Any design choices they made are bound to be qualified. E.g. have a look at the EC2 architecture and interfaces. A demonstration of an API is given  here.

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. What one is really doing is putting a job on a cluster - which is a one-off - rather than interacting with some service. Things like distributed 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