Problem

When upgrading Confluence Data Center to 6.10 or later, the following error appears in the application log:

ERROR [localhost-startStop-1] [atlassian.confluence.cluster.DefaultClusterConfigurationHelper] lambda$saveSharedProperty$3 Could not save access.mode into the shared confluence.cfg.xml file: {}
com.atlassian.config.ConfigurationException: failed to find config at: shared-home/confluence.cfg.xml
...
Caused by: java.io.FileNotFoundException: shared-home/confluence.cfg.xml (No such file or directory)

Cause

Read-only mode, introduced in Confluence 6.10, writes the access mode (whether the site is currently read only or read / write) to the confluence.cfg.xml file located in the shared home directory. 

If you installed Confluence Data Center prior to Confluence 6.1, this file will not be present in your shared home directory, as it was only created for new installs, not when you upgraded to Confluence 6.1 or later. 

Resolution

The simplest way to resolve this issue is to create the confluence.cfg.xml file in your shared home directory:

1. Copy the confluence.cfg.xml file from the local home directory on one of your Confluence nodes to your shared home directory. 

2. Edit the file, and remove all properties,  except for the following:

   <confluence-configuration>
     <setupStep>complete</setupStep>
     <setupType>cluster</setupType>
     <buildNumber>7801</buildNumber>
     <properties>
       <property name="access.mode"> ... </property>
       <property name="atlassian.license.message"> ... </property>
       <property name="confluence.cluster">true</property>
       <property name="hibernate.setup">true</property>
       <property name="jwt.private.key"> ... </property>
       <property name="jwt.public.key"> ... </property>
       <property name="lucene.index.dir">${localHome}\index</property>
     </properties>
   </confluence-configuration>

   Make sure you include the real values for each parameter and property, for example the build number, and your private and public key. We've omitted the license and keys here to make this example easier to read. 
   
   

3. Save the file, then start Confluence.