airavata-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From Raminder Singh <rsand...@gmail.com>
Subject Re: Airavata Orchestrator component
Date Fri, 06 Dec 2013 17:34:26 GMT
Lahiru: Can you please start a document to record this conversation? There are very valuable
points to records and don’t want to loose anything in email threads. 

My comments are inline with prefix RS>>: 

On Dec 5, 2013, at 10:12 PM, Lahiru Gunathilake <glahiru@gmail.com> wrote:

> Hi Amila,
> 
> I have answered questions you raised except some how to questions (for how questions
we need to figure out solutions, before that we need to come up with good design).
> 
> 
> On Thu, Dec 5, 2013 at 7:58 PM, Amila Jayasekara <thejaka.amila@gmail.com> wrote:
> 
> 
> 
> On Thu, Dec 5, 2013 at 2:34 PM, Lahiru Gunathilake <glahiru@gmail.com> 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.
RS >> We need a API method to handle this and protocol interfacing of API can be handled
separately using Thrift or Web services. 
> 
> 2. Accepts a job request and parse the input types and if input types are correct, this
will create an Airavata experiment ID.
RS >> According to me, we need to save every request to registry before verification
and have a input configuration error if the inputs were not correct. That will help us to
find if there were any API invocation errors. 
> 
> 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.
> Yes. 
RS >> I think orchestrator should call GFAC to invoke the job than GFAC polling for
the jobs. Orchestrator should make a decision that to which instance of GFAC it submit the
job and if there is a system error then bring up or communicate to another instance.I think
pull based model for GFAC will add an overhead. We will add another point of failure.  

> Further why are you saying you dont need to worry about error handling ? What sort of
errors are you considering ?
> I am considering GFAC failures or connection between Orchestrator and GFAC goes down.

>  
> 
> 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.
> I haven't seen hanged logic situation, may be there are. 
> 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 ?
> Example if gfac has an logic of picking up a job which didn't response in a given time
there could be a scenario where two gfac instances try to pick the same job. Ex: there are
3 gfac nodes working and one goes down with a given job. And two other nodes recognize this
at the same time and try to launch the sam ejob. I was talking about locks to fix this issue.
RS >> One way to handle is to look at job walltime. If the walltime for a running job
is expired and we still don’t have the status of the job then we can go ahead and check
the status and start cleaning up the job. 
>  
> 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.
> Yes you are correct, I am assuming we are mostly focusing on implementing more reliable
system and most of these jobs are running hours, and we don't need to implement high performance
system for a system with  long running jobs. 
RS >> We need to discuss this. I think orchestrator should only maintain state of request
not GFAC.
> 
> 3. What is the strategy to divide jobs among GFAC instances ?
> Not sure, we have to discuss it. 
> 
> 4. How to identify GFAC instance is failed ?
> 
> 5. How GFAC instances should be registered with the orchestrator ?
RS >> We need to have a mechanism which record how many GFAC instance are running and
how many jobs per instance.  
> 
> 6. How job cancellations are handled ?
RS >> Single job canceling is simple and should have a API function to cancel based
on experiment id and/or local job id. 
> 
> 7. What happend if Orchestrator goes down ?
> This is under assumption Orchestrator doesn't go down (Ex: as a Head node in Map reduce).

RS >> I think registration of job happen outside orchestrator and orchestrator/GFAC
progress the states.  
> 
> 8. Does monitoring execution paths go throug Orchastrato ?
> I intensionally didn't mention about monitoring, how about we discuss it separate. 
> 
> 9. How does fail over work ? 
> 
> What do you mean and whose fail over ? 
>  
> 
> 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 resource
> I agree, there could be few important states like
> input transfered, job submitted, job finished, output transfered.
> 
> 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. 
> +1. 
> 
> To precisely implement this we need a 2-phase commit like mechanism. Then we can make
sure jobs will not duplicate.
> +1.
> 
> 
> Thanks amila for compiling the email carefully.
> 
> Regards
> Lahiru 
> 
>  
> 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
> 
> 
> 
> 
> -- 
> System Analyst Programmer
> PTI Lab
> Indiana University


Mime
View raw message