Goals This guide describes how to configure a high availability cluster of Neo4j Enterprise. It includes topics such as data synchronization, mending procedures, configuring an arbiter, and slave-only mode configuration. Prerequisites You should know how to download and install Neo4j… Learn More →
This guide describes how to configure a high availability cluster of Neo4j Enterprise. It includes topics such as data synchronization, mending procedures, configuring an arbiter, and slave-only mode configuration.
You should know how to download and install Neo4j on your system. If you are a developer, you should be accustomed to the graph data model and have written your Neo4j application. A sound understanding of Neo4j’s APIs, tuning, security, and upgrade aspects will help you set up a stable cluster.
Overview
Data Synchronization between master and slaves
The Neo4j High Availability Cluster is a fault tolerant, full master-slave replication setup. Any data (graph or index) created on the master is propagated to the slaves depending on the settings of the master ha.tx_push_factor (number of slaves to actively push to during commit) and slaves ha.pull_interval (frequency of pulling updates from the master).
Configuring a Two-Slave Cluster with an Arbiter
There’s a step-by-step tutorial for setting up a HA cluster. For a two-node cluster, you’ll actually want to run three separate machines, and use the Neo4j arbiter on the third. Details on the arbiter are available in the Neo4j Manual. The configuration for the arbiter is identical to that of a regular instance, with the exception of anything relating to the actual graph database itself (since an arbiter doesn’t hold any data).
The ha.initial_hosts property should be the same on all the instances, including the arbiter. The arbiter should have a unique ha.server_id (3 is fine).
Setting a Server in Slave-Only Mode
See the documentation on ha.slave_only.
You might want to configure a machine with that setting if it’s acting as a reporting instance but you need to make sure that two members don’t have that setting, or you won’t have any failover in the cluster.
Backing Up a Cluster Server
Neo4j Server must be configured to run a backup service. This is enabled via the configuration parameter online_backup_enabled, and is enabled by default. The interface and port the backup service listens on is configured via the parameter online_backup_server and defaults to the loopback interface and port 6362. It is typical to reconfigure this to listen on an external interface, by setting online_backup_server=<my-host-ip-address>:6362. It can also be configured to listen on all interfaces by setting online_backup_server=0.0.0.0:6362.
It is best to use the back tool with the command line ./bin/neo4j-backup -host 192.168.1.34 -to /mnt/backup/neo4j-backup, which will backup the store from that specific host even if that host is running in a cluster.
Additional details can be found in the manual.
Mending Procedure for Master
- Shut down all members of the cluster and stop any load against the cluster
- On the master instance, copy the
data/graph.dbfolder as a backup - Modify neo4j-server.properties, setting the
org.neo4j.server.database.modeto STANDALONE` - Start the database and, once it’s running, stop it again (this is to ensure he database is cleanly shut down)
- Remove all files named
nioneo_logical.log.vXXindata/graph.db, being careful not to remove any files without the “v”, likenioneo_logical.log.1ornioneo_logical.log.active - Start the server and use either neo4j-shell or the neo4j browser to issue the following two queries:
- First query. Note the id returned here
CREATE (n) RETURN id(n)- Second query. Use the id returned from the previous query
MATCH (n) WHERE id(n) = <your node id> DELETE n- Stop the server
- Set org.neo4j.server.database.mode to HA
- Start the server
Mending Procedure for Slaves
- On each slave, remove the
data/graph.dbfolder - Start the slave, and watch
data/graph.dbfor it to copy the store from the master - Once copying is done, move to do the same thing on the second slave
