Intra-cluster encryption
Enterprise Edition

Securing client-to-server communication is not covered in this chapter (e.g. Bolt, HTTPS, Backup).

Introduction

The security solution for cluster communication is based on standard SSL/TLS technology (referred to jointly as SSL). Encryption is one aspect of security, the other cornerstones are authentication and integrity. A secure solution is based on a key infrastructure which is deployed together with a requirement of authentication.

The SSL support in the platform is documented in detail in SSL framework. This section covers the specifics as they relate to securing a cluster.

Under SSL, an endpoint can authenticate itself using certificates managed by a Public Key Infrastructure (PKI).

The deployment of a secure key management infrastructure is beyond the scope of this manual, and should be entrusted to experienced security professionals. The example deployment illustrated below is for reference purposes only.

Example deployment

Generate and install cryptographic objects

The generation of cryptographic objects is for the most part outside the scope of this manual. It generally requires having a PKI with a Certificate Authority (CA) within the organization and they should be able to advise here. Note that the information in this manual relating to the PKI is mainly for illustrative purposes.

If setting up intra-cluster encryption as part of a cluster configuration, ensure that the certificates used on the cluster endpoint support server and client usage. This is because when connecting between the Neo4j servers for clustering, each server uses its own certificate to authenticate as a client on the connection to another server.

This could be verified from within the certificate details:

openssl x509 -in public.crt -noout -text

You should see that the X509v3 Extended Key Usage section shows both the usages listed:

X509v3 Extended Key Usage:
    TLS Web Server Authentication, TLS Web Client Authentication

When the certificates and private keys are obtained they can be installed on each of the servers. Each server has a certificate of its own, signed by a CA, and the corresponding private key. The certificate of the CA is installed into the trusted directory, and any certificate signed by the CA is thus trusted. This means that the server now has the capability of establishing trust with other servers.

Be sure to exercise caution when using CA certificates in the trusted directory, as any certificates signed by that CA are then trusted to join the cluster. Never use a public CA or your internal root CA to sign certificates for your cluster. Instead, use an intermediate certificate or a CA certificate which originates from and is controlled by your organization, and is only used for that specific cluster.

In this example a mutual authentication setup is deployed, which means that both ends of a channel have to authenticate. To enable mutual authentication the SSL policy must have client_auth set to REQUIRE (which is the default). Servers are by default required to authenticate themselves, so there is no corresponding server setting.

If the certificate for a particular server is compromised, it is possible to revoke it by installing a Certificate Revocation List (CRL) in the revoked directory. It is also possible to redeploy using a new CA. For contingency purposes, it is advised to have a separate intermediate CA specifically for the cluster which can be substituted in its entirety should it ever become necessary. This approach would be much easier than having to handle revocations and ensuring their propagation.

Example 1. Generate and install cryptographic objects

In this example, assume that the private key and certificate file are named private.key and public.crt, respectively. The policy configuration for the key and certificate names/locations can be overridden if different names are desired. For this server, use the default configuration, create the appropriate directory structure, and install the certificate:

$NEO4J_HOME> mkdir certificates/cluster
$NEO4J_HOME> mkdir certificates/cluster/trusted
$NEO4J_HOME> mkdir certificates/cluster/revoked

$NEO4J_HOME> cp $some-dir/private.key certificates/cluster
$NEO4J_HOME> cp $some-dir/public.crt certificates/cluster

Configure the cluster SSL policy

By default, cluster communication is unencrypted. However, even if you change the default and encrypt it, without mutual TLS, any network-reachable client can replicate the database via the cluster port. Therefore, configure a cluster to encrypt its intra-cluster communication by setting dbms.ssl.policy.cluster.enabled=true and client_auth=REQUIRE. See SSL framework → Configuration for details.

An SSL policy utilizes the installed cryptographic objects and additionally allows parameters to be configured. Use the parameters in one of the following configurations:

The following example assumes that an SSL policy is created and configured as per the example deployment and uses the default TLSv1.2.

Add the following content to the neo4j.conf file:

dbms.ssl.policy.cluster.enabled=true
dbms.ssl.policy.cluster.tls_versions=TLSv1.2 \ (1)
dbms.ssl.policy.cluster.ciphers=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384 \ (2)
dbms.ssl.policy.cluster.client_auth=REQUIRE (3)

1	With control of the entire cluster, the default TLS standard can be enforced without any concern for backwards compatibility. It has no known security vulnerabilities and uses the most modern algorithms for key exchanges, etc.
2	A particular single strong cipher can be enforced and thus remove any doubt about which cipher gets negotiated and chosen. The selected cipher offers Perfect Forward Secrecy (PFS) and uses the Advanced Encryption Standard (AES) for symmetric encryption. AES has great support for hardware acceleration and thus allows performance to be generally negligibly affected.
3	Setting the cluster client authentication to `REQUIRE` enables mutual authentication, meaning both ends of a channel must authenticate.

The following example assumes that an SSL policy is created and configured as per the example deployment and uses both TLSv1.2 and TLSv1.3.

Add the following content to the neo4j.conf file:

dbms.ssl.policy.cluster.enabled=true
dbms.ssl.policy.cluster.tls_versions=TLSv1.3,TLSv1.2 \ (1)
dbms.ssl.policy.cluster.ciphers=TLS_AES_256_GCM_SHA384,TLS_AES_128_GCM_SHA256,TLS_RSA_WITH_AES_256_CBC_SHA,TLS_DHE_DSS_WITH_AES_256_CBC_SHA,TLS_RSA_WITH_AES_128_CBC_SHA \ (2)
dbms.ssl.policy.cluster.client_auth=REQUIRE \(3)

1	With control of the entire cluster, the default TLS standard can be enforced without any concern for backwards compatibility. It has no known security vulnerabilities and uses the most modern algorithms for key exchanges, etc.
2	If you want to specify ciphers for both supported TLS versions, you must specify ciphers for each TLS version not to get more ciphers than expected. The selected ciphers offer Perfect Forward Secrecy (PFS) and use the Advanced Encryption Standard (AES) for symmetric encryption. AES has great support for hardware acceleration and thus allows performance to be generally negligibly affected.
3	Setting the cluster client authentication to `REQUIRE` enables mutual authentication, meaning both ends of a channel must authenticate. They have no known security vulnerabilities and use the most modern algorithms for key exchanges, etc.

Any user data communicated between servers is now secured. Note that a server that is not correctly setup is not able to communicate with the others.

The policy must be configured on every server with the same settings. The actual cryptographic objects installed are mostly different since they do not share the same private keys and corresponding certificates. However, the trusted CA certificate is shared.

Validate the secure operation of the cluster

To make sure that everything is secured as intended, it makes sense to validate using external tooling such as, for example, the open source assessment tools nmap or OpenSSL.

Example 2. Validate the secure operation of the cluster

This example uses the nmap tool to validate the secure operation of the cluster. A simple test to perform is a cipher enumeration using the following command:

nmap --script ssl-enum-ciphers -p <port> <hostname>

The hostname and port have to be adjusted according to the example configuration. This can prove that TLS is in fact enabled and that only the intended cipher suites are enabled. All servers and all applicable ports should be tested.

For testing purposes, it is also possible to utilize a separate testing instance of Neo4j which, for example, has an untrusted certificate in place. The expected result of this is that the test server is not able to participate in replication of user data. The debug logs generally indicate an issue by printing an SSL or certificate-related exception.

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).

Intra-cluster encryptionEnterprise Edition