Mirror other than content

By default mirroring handles content (and resources used by content such as linked files or PageObjects). I have heard some feedback that it would be nice if mirroring handled other things as well, in that specific case the question was regarding including page types. We might add page types and other things to mirroring “out of the box”, but for now it is possible to write a module that extends mirroring with that. In this post I will present a simple module that will include page types, dynamic property definitions, categories and tab definitions to the mirroring process.

NOTE: To be able to mirror page types you must uncheck “Enable validation” on the mirroring channel configuration. Otherwise the mirroring job will fail with a validation error if page types differ. The mirroring will handle creation of new page types and properties on page types but it will not handle deletion of page types or properties.

It is also possible to mirror other types of data. Data stored in DDS can be mirrored by simply adding the Identity of the objects to mirror to the EPiServer.Enterprise.DynamicDataTransferHandler. It is also possible to write an own import/export handler that gives you an exclusive stream to handle custom data. See my related post here regarding export of custom data and DDS data.

Access rights can be mirrored by combining this module with a prior module I wrote. There are however some settings/data that are not handled by this module (or the prior module), like Users, Groups, Enabled languages, workflow definitions etc. Some of them can probably be mirrored by writing a custom module but for example users is tricky since the passwords are hashed and thereby not readable.

One use case for mirroring is backup/failover. If you mirror your whole site then you will always have a running backup which also uses another database meaning that even if the “original” database for some reason goes down you could switch traffic to the mirrored site.

This code goes with standard “works on my machine” so any use of it is of own risk and unsupported. The module should be deployed to the bin folder of the Mirroring service on the source side.

 [InitializableModule()]
    public class MirrorAdditionalContentModule : IInitializableModule
    {
        //Mirroring service executes each job in own AppDomain so 
        //we dont have to worry about several jobs executing in parallell.
        private bool _exportedData = false;

        public void Initialize(InitializationEngine context)
        {
            MirroringEvents.SourceStartingJob +=
                delegate(object source, MirroringSourceInitializeEventArgs args)
                {
                     DataExporter.Exporting +=
                        new EventHandler(DataExporter_Exporting);
                };        
        }

        void DataExporter_Exporting(object sender, EventArgs e)
        {
            //There might be several packages in one job, 
            //send "extra" data only in first package
            DataExporter exporter = sender as DataExporter;
            if (!_exportedData && exporter.TransferType == 
                TypeOfTransfer.MirroringExporting)
            {
                _exportedData = true;
                
                //Unfortunately there is no easy way to keep track 
                //of changes on pagetypes, dynamic properties etc.
                //Therefore we always send all and let destination service merge.
                
                exporter.PageTypes.AddRange(PageType.List());
                exporter.DynamicPropertyDefinitions.AddRange(
                    PageDefinition.ListDynamic());
                exporter.TabDefinitions.AddRange(TabDefinition.List());
                foreach (int catId in CategoryList.LoadCategories())
                {
                    exporter.Categories.Add(Category.Find(catId));
                }
            }
        }

        public void Preload(string[] parameters) { }

        public void Uninitialize(InitializationEngine context)
        {
        }
       
    }