Backup and Restore Extension for the management of ImageMosaic indexers

Introduction

ImageMosaics CoverageStores make use of several .properties files instructing the reader on how to create the mosaic index.

What we want to achieve is to allow the GeoServer Backup & Restore module to inject environment properties on indexers allowing the ImageMosaic to be automatically ported among different environments.

Technical Details

The GeoServer Backup & Restore module actually provides an extension point on reading / writing allowing GeoServer to handle additional resources related to a particular ResourceInfo.

The interfaces :

public interface CatalogAdditionalResourcesWriter<T> {

    public boolean canHandle(Object item);

    public void writeAdditionalResources(Backup backupFacade, Resource base, T item)
            throws IOException;

}

public interface CatalogAdditionalResourcesReader<T> {

    public boolean canHandle(Object item);

    public void readAdditionalResources(Backup backupFacade, Resource base, T item)
            throws IOException;

}

Is invoked by the CatalogFileWriter (when doing a Backup) and the CatalogItemWriter (when doing a Restore) after a successful write of the resource configuration on the, respectively, target backup folder and in-memory catalog.

The idea is the following one allowing the CatalogItemWriter to:

1. Restore the ImageMosaic Indexer Properties injecting environment properties
2. Check if the Mosaic index physically exist and if not create an empty one

In order to do that we envisage the following technical approach

On a BACKUP operation

1. The Additional Resource Writer checks if the ResourceInfo is an ImageMosaic Coverage Store.
2. The Additional Resource Writer looks for *.template files on the ImageMosaic index directory. It must store them into the zip archive by reading the path from the Coverage Store.
3. The Additional Resource Writer stores the *.template along with the *.properties files on the target backup folder. Same as above.

On a RESTORE operation

1. The Additional Resource Reader checks if the ResourceInfo is an ImageMosaic Coverage Store.
2. The Additional Resource Reader looks for *.template files on the ImageMosaic index directory. It will try to restore them by using the path read from the Coverage Store configuration.
3. The Additional Resource Reader overwrites the *.properties files by resolving all the environment properties declared on the templates.
4. The Additional Resource Reader checks if the empty mosaic must be created or not.