Understanding Rolling Upgrades
A rolling upgrade incrementally installs a later version of MarkLogic Server (host by host), rather than having to take down the whole cluster to install the newer version. Performing a rolling upgrade means that your cluster may be in a mixed state (where more than one version of MarkLogic Server is running) for some period of time during the upgrade process. During the process, the features in the newer version of MarkLogic will not be available until the whole cluster has been committed to the new version. Because of this you may have to change or modify some of your application code prior to starting the rolling upgrade, so that code will work in a mixed environment. For example, JavaScript code may need modification (because of the new version of V8 for server-side JavaScript) before you commit the upgrade.
The primary security, schema, and auxiliary forests must be on the same host, and that host should be the first host you upgrade when upgrading a cluster.
Note
In a mixed node cluster, before the upgrade has been committed, the node that has been upgraded will be read-only. This only applies to server configuration and not content databases. This is to prevent any configuration changes from the node. We strongly recommend that you not make any configuration changes until you have finished upgrading the entire cluster.