Read-only replicated server difficulties

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johnwalsh

Hi,

I have two Alfresco servers, and am using rsync and mysql replication to replicate the master to the slave. The slave is set to read-only. I'm running into a series of bootstrap problems where I need to change Java bootstrap routines to not do the bootstrap operation if the instance is in read-only mode. So far, I've changed WorkflowInterpreter.java, DictionaryRepositoryBootstrap.java and DescriptorServiceImpl.java to wrap the functional parts of the bootstrap routines in "if (!transactionService.isReadOnly())" statements. The bootstrap operations in question are trying to affect changes to the repository and are failing because the repository is read-only.

I assume more classes will need changing before I'm done, and/or that something I'm commenting out will cause other problems that I'll have to deal with.

Is there a simpler way to make Alfresco replication with a read-only slave work? Have others done this?


FWIW: here's the way I'm setting the slave to read-only: alfresco/domain/transaction.properties

server.transaction.mode.readOnly=PROPAGATION_REQUIRED, readOnly
server.transaction.mode.default=PROPAGATION_REQUIRED, readOnly
server.transaction.allow-writes=false
server.transaction.max-retries=20
‍‍‍‍‍

Thanks,
John

johnwalsh

It looks to me like repository replication can't work. The wiki sure seems to state that it does, and I'd sure like to be wrong wrong:


My slave instance is now proceeding through the boot process as far as the ModuleComponentHelper where the custom modules are started up. (I have two custom modules.) That work is done within a transaction. The attempt to get a transaction was failing because I have transactions configured to readOnly. My code can't skip custom module startup and still behave as desired, so I changed RetryingTransactionHelper to return a read-only transaction instead of failing when a read-write transaction is requested but the RetryingTransactionHelper's readOnly flag is set to true. My hope was that no writes would be required for the slave Alfresco instance. Unfortunately, that's not true. The following line in ModuleComponentHelper.startModule() attempts to write to the database and fails:

registryService.addProperty(moduleKeyCurrentVersion, moduleNewVersion);‍

This makes it appear that the system has to be allowed to write to the database if you need to include custom modules. For reasons documented in my previous post (conflicting primary key values), the slave in a replicated system cannot be allowed to write to the database. These conflicting truths seem to imply that Alfresco repository replication can't work if you have custom modules.

Does anyone have it working? How did you address slave writes to the database with MySQL replication of the database?

I hope I'm missing something, because repository replication is a really desirable feature. Any help would be appreciated.

Thanks,
John