The upgrade process for DataStax Enterprise is aimed at providing minimal downtime (ideally zero). With a few exceptions, the cluster will continue to work as though it were on the older version until all of the nodes in the cluster have been upgraded.
To perform an upgrade with zero downtime, we recommend performing the upgrade as a rolling restart. The procedure for the rolling upgrade is:
While the cluster is in a partially upgraded state, please observe the general limitations.
Most version upgrades also have special limitations or require special steps. These details are listed in the Version specific upgrade instructions. The steps outlined in these pages are generally cumulative, so the special instructions for all versions between your current version and the version you're upgrading to need to be followed.
The following sections examine the above steps in more detail:
Before stopping the node, run nodetool drain to flush the commit log of the old installation:
nodetool drain –h <hostname>
If you are upgrading a DSE Search/Solr node, this step is mandatory to prevent having to re-index data. This step is recommended for upgrading other nodes because it saves time when the node starts up.
Then stop the node as appropriate for your installation type.
Before installing the new product, we recommend you back up any configuration files you have modified. Depending on how you install the product, these files may be overwritten with default values during the installation.
After backing up your configuration, follow the appropriate installation instructions depending on your current installation type:
Using the backups you made of your configuration files, merge any modifications you have previously made into the new configuration files for the new version. Configuration options change often, so be sure to double check the Version specific upgrade instructions for additional steps and changes regarding configuration.
Follow the steps appropriate for your installation type:
Many times warnings, errors and exceptions will be found in the logs on starting up an upgraded node. Some of these are informational and will help you execute specific upgrade related steps. Be sure to check the Version specific upgrade instructions to identify which of these is expected, and for instructions on using these warnings and errors to complete your upgrade. If you find any unexpected warnings, errors or exceptions, contact Support.
The order of upgrading nodes matters. Please upgrade nodes in the following order: