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From Amila Jayasekara <>
Subject Re: Airavata Orchestrator component
Date Fri, 06 Dec 2013 00:58:36 GMT
On Thu, Dec 5, 2013 at 2:34 PM, Lahiru Gunathilake <>wrote:

> Hi All,
> We are thinking of implementing an Airavata Orchestrator component to
> replace WorkflowInterpreter to avoid gateway developers to dealing with
> workflows when they simply have one single independent jobs to run in their
> gateways. This component is mainly focusing on how to invoke GFAC and
> accept requests from the client API.
> I have following features in mind about this component.
> 1. It gives a web services or REST interface where we can implement a
> client to invoke it to submit jobs.
> 2. Accepts a job request and parse the input types and if input types are
> correct, this will create an Airavata experiment ID.
> 3. Orchestrtor then store the job information to registry against the
> generated experiment ID (All the other components identify the job using
> this experiment ID).
> 4. After that Orchestrator pull up all the descriptors related to this
> request and do some scheduling to decide where to run the job and submit
> the job to a GFAC node (Handling multiple GFAC nodes is going to be a
> future improvement in Orchestrator).
> If we are trying to do pull based job submission it might be a good idea
> to handle errors, if we store jobs to Registry and GFAC pull jobs and
> execute them Orchestrator component really doesn' t have to worry about the
> error handling.

I did not quite understand what you meant by "pull based job submission". I
believe it is saving job in registry and periodically GFAC looking up for
new jobs and submitting them. Further why are you saying you dont need to
worry about error handling ? What sort of errors are you considering ?

> Because we can implement a logic to GFAC if a particular job is not
> updating its status fora g iven time it assume job is hanged or either GFAC
> node which handles that job is fauiled, so  GFAC pull that job (we
> definitely need a locking mechanism here, to avoid two instances are not
> going to  execute hanged job) and  start execute it. (If GFAC is handling a
> long running job still it has to update the job stutus frequently with the
> same status to make sure GFAC node is running).

I have some comments/questions on this regard;

1. How are you going to detect that job is hanged ?

2. We clearly need to distinguish between fault jobs and fault GFAC
instances. Because GFAC replication should not pick the job if its logic is
leading to hang situation. GFAC replication should pick the job only if
primary GFAC instance is down. I believe you proposed locking mechanism to
handle this scenario. But I dont see how locking mechanism going to resolve
this situation. Can you explain more ?

2. According to your description, it seems there is no communication
between GFAC instance and Orchastrator. So GFAC and Orchastrator exchange
data through registry (Database). Performance might drop since we are going
through persisting mediums.

3. What is the strategy to divide jobs among GFAC instances ?

4. How to identify GFAC instance is failed ?

5. How GFAC instances should be registered with the orchastrator ?

6. How job cancellations are handled ?

7. What happend if Orchestrator goes down ?

8. Does monitoring execution paths go throug Orchastrato ?

9. How does fail over work ?

> 5. GFAC creates its execution chain and store it back to registry with
> experiment ID, and GFAC updates its states using check pointing.
> 6. If we are not doing pull based submission,during a GFAC failure
> Orchestrator have to identify it and submit the active jobs from failure
> gfac node  to other nodes.

I think there is more communication need to happend here.
1. When Orchastrator first deposit the job it should be unsubmitted state.
2. GFAC should only update state to active after really submitting it to

Incase of a GFAC instance failure the secondary GFAC should go through all
unfinished jobs relevant to failed and get there state by consulting the
resource. If those jobs are still in active state monitoring mechanism
should be established. We only need to re-submit jobs if they are in
unsubmitted state.

To precisely implement this we need a 2-phase commit like mechanism. Then
we can make sure jobs will not duplicate.

> This might cause job duplication in case Orchestrator falls alarm about
> GFAC failure (so have to handle carefully).
> We have lot more to discus about the GFAC but I limit our discussion to
> Orchestrator component for now.
> WDYT about this design ?
> Lahiru
> --
> System Analyst Programmer
> PTI Lab
> Indiana University

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