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1. Update to your latest minor release version first before upgrade to recent major release. A May 2017 example: a customer was considering an upgrade from 5.4.1 to 5.5.4 (latest release at that time). The correct sequence would have been: 5.4.1 → 5.4.12 → 5.5.4 instead of  5.4.1 → 5.5 → 5.5.4.
2. Carefully look for "change" or "changes for ..." sections in the release notes since.
3. Because the upgrade process takes time and is vulnerable to incidents, please minimize the risk by cleaning up your system, removing unused data, reindexing everything and doing a full backup first.

Specific points

Default JCR persistency layer in Magnolia 5.6

The default JCR persistency layer in Magnolia 5.6 is H2, which is reflected in the following setting of the magnolia.repositories.jackrabbit.config property in the magnolia.properties file:

magnolia.repositories.jackrabbit.config=WEB-INF/config/repo-conf/jackrabbit-bundle-h2-search.xml

If you used a different database before upgrading to Magnolia 5.6, make sure you keep your magnolia.repositories.jackrabbit.config setting. For Apache Derby, for example this would be: 

magnolia.repositories.jackrabbit.config=WEB-INF/config/repo-conf/jackrabbit-bundle-derby-search.xml n your magnolia.properties file.  

Vaadin 8 and your custom modules

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<dependencyManagement>
 <dependencies>
  <dependency>
   <groupId>info.magnolia.boms</groupId>
   <artifactId>magnolia-external-dependencies</artifactId>
   <version>5.6</version>
   <type>pom</type>
   <scope>import</scope>
  </dependency>
 </dependencies>
</dependencyManagement>

Default JCR persistency layer in Magnolia 5.6

The default JCR persistency layer in Magnolia 5.6 is H2, which is reflected in the following setting of the magnolia.repositories.jackrabbit.config property in the magnolia.properties file:

magnolia.repositories.jackrabbit.config=WEB-INF/config/repo-conf/jackrabbit-bundle-h2-search.xml

If you used a different database before upgrading to Magnolia 5.6, make sure you keep your magnolia.repositories.jackrabbit.config setting. For Apache Derby, for example this would be: 

magnolia.repositories.jackrabbit.config=WEB-INF/config/repo-conf/jackrabbit-bundle-derby-search.xml n your magnolia.properties file.  

Using Standard Templating Kit (STK)?

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