topic Re: Could multiple Activiti engines share one Repository? in Alfresco Archive

Could multiple Activiti engines share one Repository?

mscai — Tue, 12 Apr 2011 05:48:07 GMT

If multiple Activiti engines share one Repository DB, are there any issues?In this environment, could each Activiti engine work independently?In this environment, how could I query tasks, process instances which belong to the current activiti engine? It seems ProcessInstanceQuery and TaskQuery don't

Re: Could multiple Activiti engines share one Repository?

jbarrez — Tue, 12 Apr 2011 08:05:35 GMT

If multiple Activiti engines share one Repository DB, are there any issues?
In this environment, could each Activiti engine work independently?

Yes, no problem at all. That's how Activiti works in a clustered environment.

In this environment, how could I query tasks, process instances which belong to the current activiti engine? It seems ProcessInstanceQuery and TaskQuery don't provide this functionality.

What do you mean with 'current engine'. That doesnt seem like you want to have a common repository. If you want data per engine, you need to have a separate db per engine.

My use case is a HA system. There are some active processes. Each process contains one activiti engine, and execute workflow. There are other processes which are called as backup processes. These processes do nothing. If one active process crashes, there would be backup process selected. This backup process takes up the responsibility of the crashed active process. It start a activiti engine and continue to execute workflows.

With process you dont mean a BPM 'process', right?
Your use case would be much easier solved by running multiple Activiti engines in a cluster.

Re: Could multiple Activiti engines share one Repository?

mscai — Fri, 15 Apr 2011 03:37:53 GMT

Yes, no problem at all. That's how Activiti works in a clustered environment.

I am new to Activiti. Could you tell me where could I get the doc or detailed instruction about Activiti in clustered environment, please?
Thank you.

What do you mean with 'current engine'. That doesnt seem like you want to have a common repository. If you want data per engine, you need to have a separate db per engine.

"Current engine" means the activiti engine owned by the current application.
I want a common repository for all activiti engine.

With process you dont mean a BPM 'process', right?
Your use case would be much easier solved by running multiple Activiti engines in a cluster.

No, it is not a BPM 'process'. It is application.

Re: Could multiple Activiti engines share one Repository?

jbarrez — Fri, 15 Apr 2011 08:17:34 GMT

I am new to Activiti. Could you tell me where could I get the doc or detailed instruction about Activiti in clustered environment, please?

Currently, no docs on that topic. But basically you can set up multiple engine on multiple web containers, and point them to the same database. We've made sure that works perfect out of the box.

"Current engine" means the activiti engine owned by the current application.
I want a common repository for all activiti engine.

So you want to split data for each applictation? Then I think it is easier to have a separate database for each application.

Re: Could multiple Activiti engines share one Repository?

anupradhan — Tue, 09 Aug 2011 14:17:03 GMT

Seeing that the post was last year, are there any documents that provide detailed instruction about Activiti in clustered environment? I did not see anything in the user guide.

Re: Could multiple Activiti engines share one Repository?

ronald_van_kuij — Tue, 09 Aug 2011 21:34:34 GMT

Read what jbarrez wrote… There is effectively nothing special to do, other than to have all engines in the 'cluster' point to te same db

Re: Could multiple Activiti engines share one Repository?

erny18031 — Tue, 15 Nov 2011 13:15:17 GMT

Read what jbarrez wrote… There is effectively nothing special to do, other than to have all engines in the 'cluster' point to te same db

Hmmm, I'm wondering if Activiti uses Hibernate and L2 Ehcache indirectly (through Spring). It seems that it currently doesn't.

I've looked into the source:
modules/activiti-engine/src/main/java/org/activiti/engine/impl/cfg/ProcessEngineConfigurationImpl.java

and it seems to use Ibatis / Mybatis.

Process definitions seem to be cached. What else?

What has to been taken into account (regarding any cached data) whenever a multi-node Activiti cluster is configured?

Regards.
Erny

Re: Could multiple Activiti engines share one Repository?

trademak — Tue, 15 Nov 2011 15:15:18 GMT

Hi,

What's your reasoning for asking?
Because the process definitions are just cached for performance reasons. So every engine in the cluster will have these definitions cached.

Best regards,

Re: Could multiple Activiti engines share one Repository?

erny18031 — Tue, 15 Nov 2011 17:08:04 GMT

Hi,

What's your reasoning for asking?
Because the process definitions are just cached for performance reasons. So every engine in the cluster will have these definitions cached.

Best regards,

Hello.

Just thinking about scalabilty and clusterization issues.

What happens if a new process version is deployed on a node? Do the other nodes pick up automatically the new process definition when a new process instance is created?

I still have not a good knowledge about such details. I'll browse the code for it. Intuitively I would think that the cached process definition is only used for already running process instances.

Regards.
Erny

Re: Could multiple Activiti engines share one Repository?

bwestrich — Wed, 30 Nov 2011 20:48:49 GMT

We are hoping to use Activiti in a clustered environment to ensure high availability. I'm glad to see jbarrez's note stating that Activiti is designed to be cluster-compatible out of the box.

However, the Activiti roadmap (at http://docs.codehaus.org/display/ACT/Roadmap) has the following item on it:
"Test clustering (Tom)"
(though there is also a caveat on the roadmap page that the roadmap may be out of date).

Has Activiti yet been tested in a clustered environment?

In particular, we are not interested in the JobExecutor functionality (as we don't use timers). Most discussion related to clusters focuses on that. We are instead interested in the overall stability of Activiti in a cluster. Specifically, we wonder if there are multi-threaded synchronizations that occur in the Activiti Java code (e.g. Java synchronize blocks) to ensure process instances are not concurrently modified in invalid ways, and if so whether these synchronizations are supplemented with the database-based locking needed to ensure thread safeness across cluster nodes.

Re: Could multiple Activiti engines share one Repository?

trademak — Thu, 01 Dec 2011 08:21:30 GMT

Hi,

Yes Activiti is cluster friendly. There is no code other than the job executor that requires specific logic to support clustering.
When all cluster nodes point to the same database, it should work fine.
Are you also not planning to use the async continuations functionality? Because that requires the use of the job executor as well.

Best regards,

Re: Could multiple Activiti engines share one Repository?

arvin_wang — Thu, 23 Aug 2012 12:24:15 GMT

hi, guys

suppose this case: i have two engines(engineA and engineB) deployed on two nodes(nodeA,nodeB) respectively. and the
two engines share one db. is it possible that the jobExecutor created by engineA only fetches the process jobs started by engineA and jobExecutor created by engineB only fetches the jobs started by engienB?

Re: Could multiple Activiti engines share one Repository?

chris_joelly — Sun, 26 Aug 2012 10:30:34 GMT

what do u mean with "jobs started by engineA" ?

i think every engine's job executor will 'start' all jobs it finds in the database. So they will run on all machines concurrently. Imagine a start-timer-event, which starts a process instance. You will get process instances of the same process definition on all nodes, and if these process instances work on the same data, eg. JPA entities, you will probably run into a messy situation.

Another tricky thing is when you have asymmetric clusters, i mean not all machines have access to the same resources and the process instances rely on specific resources. If you do not start process instances via start-timer-events you can control where they are executed. But with timer-boundary-events it might happen that execution continues on a node which does not have access to a needed resource.

At least this is what i assume would happen in a clustered environment together with the standard JobExecutor…

Re: Could multiple Activiti engines share one Repository?

meyerd — Mon, 27 Aug 2012 04:33:31 GMT

As Tijs points out, you can have multiple intances of the activiti engine running against the same database.

In such a scenario, the job executor of each activiti instance will poll the database for jobs. The jobexecutors will make sure that each job is only executed once (sucessfully). To give this guarantee, the jobexecutor locks jobs in the database.
To come back to your scenario, if you have a job executor active on nodeA and a job executor on nodeB and there is a single job in the database, the job will either be executed by nodeA or node B.

If executing the job requires access to external resources (java classes, persistence units etc…) provided by the environment, you must make sure that these resources are available on each node.

See also:
https://app.camunda.com/confluence/display/foxUserGuide/Job+Execution

Re: Could multiple Activiti engines share one Repository?

arvin_wang — Wed, 29 Aug 2012 10:52:12 GMT

"jobs started by engineA" means jobExecutor in engineA only gets the jobs created by engineA from the db.
now i want to add a field in table JOB distinguishing jobs of different engines. i do not know whether it is ok.

another demand: i want to suspend or activate a executing process instance, but the APIs provided by
activiti (such as suspendProcessInstanceById, etc) seem not to satisfy. btw, the process instance contains
many serviceTasks and these serviceTasks are set asyc.