Deploy a basic cluster
Enterprise Edition

The first step in setting up a cluster infrastructure is configuring a number of servers to form a cluster that you can host your databases on. The following configuration settings are important to consider when deploying a new cluster. See also cluster settings reference for more detailed descriptions.

Table 1. Important settings for clusters
Setting name	Description
`server.default_advertised_address`	The address that other machines are told to connect to. In the typical case, this should be set to the fully qualified domain name or the IP address of this server.
`server.default_listen_address`	The address or network interface this machine uses to listen for incoming messages. Setting this value to `0.0.0.0` makes Neo4j bind to all available network interfaces.
`dbms.cluster.endpoints`	A comma-separated list of endpoints that a server should contact in order to discover other cluster members. Typically, all cluster members, including the current server, must be specified in this list. The behavior of this setting can be modified by configuring the setting `dbms.cluster.discovery.resolver_type`. This is described in detail in Cluster server discovery.
`dbms.cluster.minimum_initial_system_primaries_count`	Minimum number of machines initially required to form a clustered DBMS. The cluster is considered formed when at least this many members have discovered each other, bound together, and bootstrapped a highly available `system` database. The default value is `3`. As a result, at least this many of the cluster’s initial machines must have `server.cluster.system_database_mode` set to `PRIMARY`.
`server.cluster.system_database_mode`	Users must manually specify the mode for the `system` database on each server. The default value is `PRIMARY`.
`initial.dbms.default_primaries_count`	The initial number of database copies in primary role. If not specified, it defaults to one copy in primary role.
`initial.dbms.default_secondaries_count`	The initial number of database copies in secondary role. If not specified, it defaults to zero copies in secondary role.
`initial.server.mode_constraint`	Specifies the server mode - whether it can host only primary databases, only secondary databases, or both types. Initialized at the first DBMS startup. When a new server is added to the cluster, the setting is used as the default input for the `ENABLE SERVER` command; can be overriden when the command is executed.
`initial.server.allowed_databases`	List of database names allowed on this server; all others are denied. When a new server is added to the cluster, the setting is used as the default input for the `ENABLE SERVER` command; can be overriden when the command is executed.
`initial.server.denied_databases`	List of database names not allowed on this server. Empty means nothing is denied. When a new server is added to the cluster, the setting is used as the default input for the `ENABLE SERVER` command; can be overriden when the command is executed.
`initial.server.tags`	A list of server tag names used by the database allocation and when configuring load balancing and replication policies. Initialized at the first DBMS startup and/or when a newly added server is enabled. The setting is used as the default input for the `ENABLE SERVER` command; can be overriden when the command is executed.

Points to consider:

Any setting with the initial prefix is effective on the first startup of the DBMS and/or when a new server joins the cluster and has to be explicitly ENABLED.
Changing the default number of primaries and secondaries dynamically can only be done with the dbms.setDefaultAllocationNumbers procedure. See CREATE DATABASE for more information.
To view the current default settings, use the dbms.showTopologyGraphConfig procedure.

Configuring any listen address to be something other than localhost, 127.0.0.1, or another loopback address, will expose the Neo4j process to connections from outside of the server that it is running on.

Make sure you understand the security implications and strongly consider setting up encryption.

Configure a cluster with three servers

The following example shows how to set up a basic cluster with three members hosting the default database, neo4j (in addition to the system database), in primary mode, using the method of server addresses list.

Depending on the type of dbms.cluster.discovery.resolver_type currently in use, the discovery service can use a list of server addresses, DNS records, or Kubernetes services to discover other servers in the cluster.

In this case, you set dbms.cluster.discovery.resolver_type=LIST.

Configure a cluster with three servers hosting databases in primary mode

In this example, three servers named server01.example.com, server02.example.com and server03.example.com are configured. Neo4j Enterprise Edition is installed on all three servers. They are configured by preparing neo4j.conf on each server.

Note that they are all identical, except for the configuration of server.default_advertised_address.

Besides, in the example below, the dbms.cluster.minimum_initial_system_primaries_count setting is not configured, as it defaults to three, and a cluster of three servers is being deployed. However, in case of setting up a cluster with only two servers, the setting dbms.cluster.minimum_initial_system_primaries_count must be set to 2 on all servers.

Prepare neo4j.conf files on each server.

neo4j.conf on server01.example.com:

server.default_listen_address=0.0.0.0
server.default_advertised_address=server01.example.com
dbms.cluster.endpoints=server01.example.com:6000,server02.example.com:6000,server03.example.com:6000
initial.dbms.default_primaries_count=3

neo4j.conf on server02.example.com:

server.default_listen_address=0.0.0.0
server.default_advertised_address=server02.example.com
dbms.cluster.endpoints=server01.example.com:6000,server02.example.com:6000,server03.example.com:6000
initial.dbms.default_primaries_count=3

neo4j.conf on server03.example.com:

server.default_listen_address=0.0.0.0
server.default_advertised_address=server03.example.com
dbms.cluster.endpoints=server01.example.com:6000,server02.example.com:6000,server03.example.com:6000
initial.dbms.default_primaries_count=3

The Neo4j servers are ready to be started. The startup order does not matter.

After the cluster has started, it is possible to connect to any of the instances and run SHOW SERVERS to check the status of the cluster. This shows information about each member of the cluster:

SHOW SERVERS;

+-----------------------------------------------------------------------------------------------------------+
| name                                   | address          | state     | health      | hosting             |
+-----------------------------------------------------------------------------------------------------------+
| "d6fbe54b-0c6a-4959-9bcb-dcbbe80262a4" | "server01:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
| "e56b49ea-243f-11ed-861d-0242ac120002" | "server02:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
| "73e9a990-0a97-4a09-91e9-622bf0b239a4" | "server03:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
+-----------------------------------------------------------------------------------------------------------+

Note that initialized servers are ENABLED automatically at the first DBMS startup.

Their values are taken from the initial settings.

If you need to change the server’s options, use the ALTER SERVER command.

For more extensive information about each server, use the SHOW SERVERS YIELD * command:

SHOW SERVERS YIELD *;

+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| serverId                               | name                                   | address          | state     | health      | hosting             | requestedHosting    | tags | allowedDatabases | deniedDatabases | modeConstraint | version     |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| "d6fbe54b-0c6a-4959-9bcb-dcbbe80262a4" | "d6fbe54b-0c6a-4959-9bcb-dcbbe80262a4" | "server01:7687" | "Enabled" | "Available" | ["system", "neo4j"] | ["system", "neo4j"] | []   | []               | []              | "NONE"         | "5.0.0"     |
| "e56b49ea-243f-11ed-861d-0242ac120002" | "e56b49ea-243f-11ed-861d-0242ac120002" | "server02:7687" | "Enabled" | "Available" | ["system", "neo4j"] | ["system", "neo4j"] | []   | []               | []              | "NONE"         | "5.0.0"     |
| "73e9a990-0a97-4a09-91e9-622bf0b239a4" | "73e9a990-0a97-4a09-91e9-622bf0b239a4" | "server03:7687" | "Enabled" | "Available" | ["system", "neo4j"] | ["system", "neo4j"] | []   | []               | []              | "NONE"         | "5.0.0"     |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Startup time

The instance may appear unavailable while it is joining the cluster. If you want to follow along with the startup, you can see the messages in neo4j.log.

Create new databases in a cluster

As mentioned in the Introduction, a server in a cluster can either host a database in primary or secondary mode. For transactional workloads, a database topology with several primaries is preferred for fault tolerance and automatic failover.

The database topology might prioritize secondaries over primaries if the workload is more analytical. Such configuration is optimized for scalability but it is not fault-tolerant and does not provide automatic failover. Both scenarios are covered in the following examples.

Example 1. Create a new database with three primaries

In the system database on one of the servers from the previous example, execute the following Cypher command to create a new database:

CREATE DATABASE foo
TOPOLOGY 3 PRIMARIES

If TOPOLOGY is not specified, the database is created according to initial.dbms.default_primaries_count specified in neo4j.conf. Also, if initial.dbms.default_secondaries_count is specified to any other number than 0, the second line of the command would read TOPOLOGY 3 PRIMARIES 0 SECONDARIES. Thus the number specified with TOPOLOGY overrides both initial.dbms.default_primaries_count and initial.dbms.default_secondaries_count (if applicable) provided that the specified numbers do not exceed the number of available servers.

Example 2. Create a new database with one primary and two secondaries

In the system database on one of the servers from the previous example, execute the following Cypher command to create a new database:

CREATE DATABASE bar
TOPOLOGY 1 PRIMARY 2 SECONDARIES

Note that this operation is possible even without specifying initial.dbms.default_secondaries_count in the initial configuration. Anything specified in the TOPOLOGY part of the Cypher command overrides the initial.dbms.default_secondaries_count setting.

Analytic use cases

To learn more about setting up a cluster specifically for analytic use cases, see Deploy an analytics cluster.

IPv6 support

Neo4j clusters can be deployed over IPv6 networks. IPv6 addresses must be enclosed in square brackets in all cluster address settings.

server.default_advertised_address=[2001:db8::1]
server.default_listen_address=[::]
dbms.cluster.endpoints=[2001:db8::1]:6000,[2001:db8::2]:6000,[2001:db8::3]:6000

Glossary

allocator: A component in the cluster that allocates databases to servers according to the topology constraints specified and an allocation strategy.
asynchronous replication: Asynchronous replication is used by secondary copies to poll for new transactions, which means they cannot be guaranteed to have received the most recent transactions. This enables efficient scale-out of read-performance.
Aura instance: A fully-managed DBMS represented by a single instance ID, that is running in the Neo4j Aura cloud.
auto-commit transaction: An automatically committed transaction that contains a single query.
Bolt protocol: Bolt is a protocol used for interaction between Neo4j instances and drivers.
bookmark: A marker the client can request from the cluster to ensure that it is able to read its own writes so that the application’s state is consistent and only databases that have a copy of the bookmark are permitted to respond.
category (Bloom): A category is based on a node label and is defined in a Perspective as a way of visually distinguishing nodes with the same label(s).
causal consistency: All servers in a cluster agree on the order in which transactions take place. The position of a server on the causal chain can be guaranteed using a bookmark.
cluster: A Neo4j DBMS that spans multiple servers working together to increase fault tolerance and/or read scalability. Databases on a cluster may be configured to replicate across servers in the cluster thus achieving read scalability or high availability.
client application: Software that interacts with a Neo4j server.
commit: A commit is the successful completion of a transaction, which ensures durability of any changes made. For more details, visit Operations Manual → Transaction management.
composite database: Composite databases are the means to access partitioned graph data with a single Cypher query.
constraint: Constraints are sets of data modeling rules that ensure the data is consistent and reliable.
Cypher®: Neo4j’s graph query language.
data model: A data model defines how information is organized in a database. A good data model will make querying and understanding your data easier. In Neo4j, the data models have a graph structure.
database: A database is a container used by the DBMS to manage and store graph data. The physical structure of data is controlled by the database.
database vs graph: Databases are the physical containers of graph data. Graphs are the logical structure of data in Neo4j.
Database Management System: Database Management System, or DBMS, capable of managing multiple databases. A DBMS may run on a single server, or span several servers configured as a cluster.
database schema: The prescribed property existence and datatypes for nodes and relationships.
deallocate: An act of removing a database from a server or a server from a cluster without loss of data or reduced fault tolerance.
degree (of a node): The number of relationships of a specific node; loops are counted twice.
disaster recovery: A manual intervention to restore availability of a cluster, or databases within a cluster.
driver: A software library that provides access to Neo4j from a particular programming language.
election: In the event that the Raft leader becomes unresponsive, followers automatically trigger an election and vote for a new leader.
entity: A node or a relationship.
expression (Cypher): A component of a Cypher query which produces values. It may be used in projections, as a predicate, or when setting properties on graph elements.
fabric: Fabric is the architectural design of a unified system that provides a single access point to local or distributed graph data.
fault tolerance: A guarantee that a cluster can maintain a database’s persistence and availability in the event of one or more servers failing.
follower: A primary copy of a database acting as a follower, receives and acknowledges synchronous writes from the leader.
Generative AI (GenAI): A type of artificial intelligence (AI) system that generates text, images, or other media in response to prompts.
graph: A logical representation of a set of nodes where some pairs are connected by relationships.
index: Data structure that improves read performance of a database.
knowledge graph: A specific type of graph that has an organizing principle so that a user (or a computer system) can reason about the underlying data. The organizing principle provides an additional layer of structure that adds context to support knowledge discovery.
label: Marks a node as a member of a named and indexed subset. A node may be assigned zero or more labels.
leader: A single primary copy of a database is designated as the leader. It receives all write transactions from clients and replicates writes synchronously to followers and asynchronously to secondary copies of the database.
main database: In terms of Neo4j Enterprise Studio, the database(s) containing the user’s data. Can exist in the same Neo4j deployment as the tool asset database.
motif: A description of a specific pattern within a graph.
node: A node represents an entity or discrete object in your graph data model. Nodes can be connected by relationships, hold data in properties, and are classified by labels.
operator: A symbol representing a mathematical or logical operation.
parameter: Named value provided when running a Cypher statement.
path: A sequence of nodes and the relationships connecting them, that does not contain duplicate relationships. Several paths can match a pattern.
pattern: A specific arrangement of nodes and relationships that can be matched in a graph. A pattern follows a motif.
perspective (Bloom): A Perspective defines a certain business view or domain that can be found in the target Neo4j graph. A single Neo4j graph can be viewed through different Perspectives, each tailored for a different business purpose.
primary: A copy of the database that is able to process write transactions and is eligible to be elected as a leader. It participates in fault tolerant writes as it is part of the majority required to acknowledge and commit write transactions.
primary vs secondary: In a cluster, databases can operate in either primary or secondary mode. Primary databases are able to process write and read transactions, ensuring fault tolerance. Secondary databases are replicated asynchronously from primaries, and their main purpose is to provide read scaling within the cluster.
project (Aura): An isolated environment in the unified Aura console that contains its own database instances, configurations, and resources. Preceded by tenant in the classic Aura console.
property: Properties are key-value pairs that are used for storing data on nodes and relationships.
query (Cypher): A statement that retrieves or writes information to a database.
Raft group: A group of servers that are participating in hosting a particular database in primary mode.
Raft group member: A server that is participating in a Raft group. A server can be a member of one or more groups.
Raft log: A shared log between all Raft group members that is guaranteed to be consistently updated and viewed by those members. The log contains both database data and operational state of the Raft group.
Raft protocol: The networking mechanism that enables a database to replicate its data across multiple servers to give high availability for accessing the data and high durability to the data stored.
read scaling: Distributing query load by creating additional database copies hosted in secondary mode (read-only).
relationship: A relationship represents a connection between nodes in your graph data model. Relationships connect a source node to a target node, hold data in properties, and are classified by type.
secondary: An asynchronously replicated copy of the database that provides read scaling within the cluster.
seed: A seed is a database dump or a full backup used to create a database on a cluster. This is sometimes called seeding.
server: A physical machine, a virtual machine, or a container running an instance of Neo4j. Servers can be standalone or part of a cluster.
session: A causally linked sequence of transactions.
session consistency: An alternative name for Neo4j’s causal consistency.
standalone: A single server running Neo4j and not part of a cluster.
synchronous replication: Synchronous replication requires the leader primary to replicate a transaction and block the commit until a quorum of the follower primaries acknowledges that the transaction is successfully replicated. Once the transaction is replicated, the commit is allowed to proceed. This ensures data durability and consistency within the cluster.
system database: A database used by Neo4j to store system information.
tenant (Aura): An isolated environment in the classic Aura console that contains its own database instances, configurations, and resources. Replaced by project in the unified Aura console.
tool asset database: In terms of Neo4j Enterprise Studio, the database where tools' assets are stored. This can be in the same Neo4j deployment as the main database(s) or in a separate deployment.
topology: A configuration that describes how the copies of a database should be spread across the servers in a cluster, see primary mode and secondary mode.
transaction: A transaction comprises a unit of work performed against a database. It is treated in a coherent and reliable way, independent of other transactions. Transactions comply with the ACID consistency model (atomic, consistent, isolated, and durable).