Created Update recommendations and troubleshooting (markdown)

Update-recommendations-and-troubleshooting.md

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+![](http://www.egroupware.org/wp-content/themes/egroupware/images/logo.svg)
+
+> **If something goes wrong with the update, it is in almost all cases related to the Apache or Nginx configuration on the host, and NOT Docker and the running containers!**
+
+If you are not familiar with your Apache/Nginx configuration (including https), or need to ensure only a minimal downtime, the recommendation will be always to do the **painless new installation** on a new host and then an **migration of your database and files** to the new host! Same is true if your old hosts version is no longer supported by from it distribution.
+
+# How to migrate your data from an existing 17.1 or older installation
+1. do a new installation as described for the distribution of the new host
+2. enable https using Let's Encrypt following the exzellent instructs from eg. [Digital Ocean](https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-18-04)
+3. make a database backup inside EGroupware using ***Administration >> Database backup and restore*** 
+4. rsync the files and backups from the old installation to the new server, run on the new server the following commands:
+```
+rsync -av --delete root@<ip-of-old-server>:/var/lib/egroupware/default/ /var/lib/egroupware/default/
+chown -R 33:33 /var/lib/egroupware/default
+```
+5. log into the new EGroupware using the generated ***sysop*** user and go to ***Administration >> Database backup and restore*** and restore the last backup you rsynced to the new server
+6. you can repeat steps 3. to 5. multiple times, until you are ready to use the new system productively