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## 22.4. Upgrading a Neo4j HA Cluster

This document describes the steps required to upgrade a Neo4j cluster from a previous version to 1.8 without disrupting its operation, a process referred to as a rolling upgrade. The starting assumptions are that there exists a cluster running Neo4j version 1.5.3 or newer with the corresponding ZooKeeper instances and that the machine which is currently the master is known. It is also assumed that on each machine the Neo4j service and the neo4j coordinator service is installed under a directory which from here on is assumed to be located at the /opt/old-neo4j path.

### 22.4.1. Overview

The process consists of upgrading each machine in turn by removing it from the cluster, moving over the database and starting it back up again. Configuration settings also have to be transferred. It is important to note that the last machine to be upgraded must be the master. In general, the “cluster version” is defined by the version of the master, providing the master is of the older version the cluster as a whole can operate (the 1.8 instances running in compatibility mode). When a 1.8 instance is elected master however, the older instances are not capable of communicating with it, so we have to make sure that the last machine upgraded is the old master. The upgrade process is detected automatically from the joining 1.8 instances and they will not participate in a master election while even a single old instance is part of the cluster.

### 22.4.2. Step 1: On each slave perform the upgrade

Download and unpack the new version. Copy over any configuration settings you run your instances with, taking care for deprecated settings and API changes that can occur between versions. Also, ensure that newly introduced settings have proper values (see Section 22.2, “Setup and configuration”). Apart from the files under conf/ you should also set proper values in data/coordinator/myid (copying over the file from the old instance is sufficient). The most important thing about the settings setup is the `allow_store_upgrade` setting in neo4j.properties which must be set to true, otherwise the instance will be unable to start. Finally, don’t forget to copy over any server plugins you may have. Shut down first the Neo4j instance and then the coordinator using the following commands:

    service neo4j-service stop
    service neo4j-coordinator stop

Next, uninstall both services:

    service neo4j-service remove
    service neo4j-coordinator remove

Now you can copy over the database. Assuming the old instance is at /opt/old-neo4j and the newly unpacked under /opt/neo4j-enterprise-1.8 the proper command would be:

    cp -R /opt/old-neo4j/data/graph.db /opt/neo4j-enterprise-1.8/data/

Next install Neo4j and the coordinator services, which also starts them:

    /opt/neo4j-enterprise-1.8/bin/neo4j-coordinator install
    /opt/neo4j-enterprise-1.8/bin/neo4j install

That’s it. Now check that the services are running and that webadmin reports the version 1.8. Transactions should also be applied from the master as usual.

### 22.4.3. Step 2: Upgrade the master, complete the procedure

Go to the current master and execute Step 1. The moment it will be stopped another instance will take over, transitioning the cluster to 1.8. Finish Step 1 on this machine as well and you will have completed the process.

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