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From "Alejandro Abdelnur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5303) Hadoop Workflow System (HWS)
Date Wed, 25 Feb 2009 16:21:04 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5303?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12676694#action_12676694
] 

Alejandro Abdelnur commented on HADOOP-5303:
--------------------------------------------

h4. Regarding language independence for launching WF jobs,

Yes, that is one of the motivations of the WS API.

h4. Regarding HWS being server-side,

Yes, to provide scalability, failover, monitoring and manageability. We want to move away
from client-side solutions.

With many 1000s WF jobs per day, a client-side solution running a process per WF job is not
a feasible option.

h4. Regarding leveraging existing workflow engines,

Definitely, that has been our approach from the beginning, our current implementation uses
jBPM (which uses Hibernate for persistency). 

jBPM & Hibernate are LGPL. Apache has provisions to work with LGPL, though this complicates
things a bit (for testing, integration, bundling, and potentially some extra layer of indirection).

Once there is a agreement in the Hadoop community regarding the functional spec we'd discuss
about specifics of the implementation.

We can easily replace jBPM with another implementation, and we are doing some work on this
area.

h4. Regarding naming corrections,

"hadoop" action to "map-reduce" action and "hdfs" to "fs", makes sense.

h4. Regarding HDFS generalization,

As we use FileSystem API, it's there already, it just a name thing and per previous comment
we could rename 'hdfs' to 'fs'.

h4. Regarding querying a WF job progress,

Yes, you can get the current status of the WF job, stats about completed and running actions:
start time, end time, resolved configuration values (with all EL expressions evaluated), current
status, exit transition, link to the webconsole for the action if any (ie Hadoop job webconsole
link), etc.



> Hadoop Workflow System (HWS)
> ----------------------------
>
>                 Key: HADOOP-5303
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5303
>             Project: Hadoop Core
>          Issue Type: New Feature
>            Reporter: Alejandro Abdelnur
>            Assignee: Alejandro Abdelnur
>         Attachments: hws-preso-v1_0_2009FEB22.pdf, hws-v1_0_2009FEB22.pdf
>
>
> This is a proposal for a system specialized in running Hadoop/Pig jobs in a control dependency
DAG (Direct Acyclic Graph), a Hadoop workflow application.
> Attached there is a complete specification and a high level overview presentation.
> ----
> *Highlights* 
> A Workflow application is DAG that coordinates the following types of actions: Hadoop,
Pig, Ssh, Http, Email and sub-workflows. 
> Flow control operations within the workflow applications can be done using decision,
fork and join nodes. Cycles in workflows are not supported.
> Actions and decisions can be parameterized with job properties, actions output (i.e.
Hadoop counters, Ssh key/value pairs output) and file information (file exists, file size,
etc). Formal parameters are expressed in the workflow definition as {{${VAR}}} variables.
> A Workflow application is a ZIP file that contains the workflow definition (an XML file),
all the necessary files to run all the actions: JAR files for Map/Reduce jobs, shells for
streaming Map/Reduce jobs, native libraries, Pig scripts, and other resource files.
> Before running a workflow job, the corresponding workflow application must be deployed
in HWS.
> Deploying workflow application and running workflow jobs can be done via command line
tools, a WS API and a Java API.
> Monitoring the system and workflow jobs can be done via a web console, command line tools,
a WS API and a Java API.
> When submitting a workflow job, a set of properties resolving all the formal parameters
in the workflow definitions must be provided. This set of properties is a Hadoop configuration.
> Possible states for a workflow jobs are: {{CREATED}}, {{RUNNING}}, {{SUSPENDED}}, {{SUCCEEDED}},
{{KILLED}} and {{FAILED}}.
> In the case of a action failure in a workflow job, depending on the type of failure,
HWS will attempt automatic retries, it will request a manual retry or it will fail the workflow
job.
> HWS can make HTTP callback notifications on action start/end/failure events and workflow
end/failure events.
> In the case of workflow job failure, the workflow job can be resubmitted skipping previously
completed actions. Before doing a resubmission the workflow application could be updated with
a patch to fix a problem in the workflow application code.
> ----

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