Synchronization module

The Synchronization module synchronizes a target Magnolia instance with a source instance. The module allows you to publish a large amount of content selectively. Only previously published content is transferred to the target instance. You can use the module to add content to new public instances without shutting down existing instances and impacting their ability to serve content.

The module traverses the node tree and publishes only previously published content. Content that was never published is not published during synchronization either. If content was versioned when it was published (Magnolia default behavior), the module publishes the last known version, making it possible to recover modified content.

The Synchronization module installs the Sync Instance app that allows you to manually synchronize content between author and one public instance.

Installing

<dependency>
  <groupId>info.magnolia.synchronization</groupId>
  <artifactId>magnolia-synchronization</artifactId>
</dependency>

To be able to use the Sync Instance app, add also the following module:

<dependency>
  <groupId>info.magnolia.synchronization</groupId>
  <artifactId>magnolia-synchronization-app</artifactId>
</dependency>

Compatibility with activation

If you intend to use the Synchronization module together with the Activation and Transactional Activation modules, representing an older implementation of publishing, you must also install the legacy module:

<dependency>
  <groupId>info.magnolia.synchronization</groupId>
  <artifactId>magnolia-synchronization-legacy</artifactId>
</dependency>

This legacy module:

• Has dependencies on the magnolia-module-activation and magnolia-module-exchange-transactional modules.
• Brings the synchronization compatibility module and app (magnolia-synchronization-compatibility, magnolia-synchronization-app).

Use cases

Public instance failure

Imagine that you have two public Magnolia instances. Due to hardware failure, one of them is out of operation. As you try to publish content during the outage, transactional publishing tells you that the content cannot be published because one of the public instances is down.

Since you really need to publish new content to the remaining public instance, you make a conscious decision to switch off the receiver that suffered the hardware failure. Now you can publish the content while waiting for the failed hardware to be replaced.

A few days later hardware on the failed public instance has been replaced and the server is up again. You re-enable the receiver so that all new content is published to both public instances. But you still have a problem with what to do with all the content that was published while the instance was down. Your options are:

• Republish everything to both instances. This is a time-consuming process, generates high load, and slows down your site during publishing.
• If you kept a list of the published pages, you know exactly what to publish to get them on both instances. This works well for small deployments with infrequent updates and a single editor.
• Use the Synchronization module. Set the previously broken public instance as a synchronization receiver and Magnolia will take care of syncing the missing content.

Public instance blackout

All public instances are corrupted, broken or compromised. No instances exist to serve content. A small site can deal with this by creating a new public instance and publishing all content to it. This is difficult in large deployments that have many editors, where content has already been modified since the blackout took effect, and where some pages are not yet ready to be published across the site. Use the Synchronization module to publish any previously published versions of content, even if the content was modified further, and skip any pages that were not previously published.

High load

You have a sudden high load on your site. You need to add a new public instance to deal with the load.

• You cannot shut down any of the existing public instances because you need them to deal with the load. This prevents taking a snapshot for cloning.
• You cannot publish all content from the author instance to public instances since this would unnecessarily flush the cache on them and increase load when the servers are already busy.

The solution is to create a new empty public instance and use the Synchronization module to publish content only to that instance while the existing public instances keep serving content.

Configuration

The Synchronization module is configured at Configuration > /modules/synchronization-core .

Synchronization command

Synchronization is controlled by the SynchronizationCommand (extends BaseActivationCommand ) registered in /modules/synchronization-core/commands/synchronization :

Properties:

Synchronization receivers

Configure the target instance as a receiver with subscriptions under it in /modules/synchronization-core/commands/synchronization/synchronize/receivers.

And /modules/publishing-core/config/receivers looks like this:

Manual synchronization

The Sync Instance tool allows you to manually synchronize content between author and a single public instance. The operation is performed asynchronously.

To perform a manual synchronization:

1. Select the workspace.
2. Type the path to be published.
3. Optionally select:
   1. A date (content publishing date) which you want to synchronize from.
   2. The checkbox to publish all child nodes recursively

4. Click Start. Synchronization starts within one minute of execution.

   You must wait for the job to start before starting another one. Otherwise you will overwrite the previous job.

5. Click Refresh to see the current status of the synchronization.

Path examples:

Scheduling synchronization

You can schedule synchronization jobs using the Scheduler module. The purpose of scheduling is not to synchronize an instance repeatedly, because this leads to unnecessary flushing of the cache and increases load. The aim is to schedule the sync to occur at a convenient later time such as during low traffic volume.

To configure a synchronization receiver, copy the /modules/scheduler/config/jobs/demo node and edit its properties.

Properties: