Scale a Neo4j deployment

Neo4j supports both vertical and horizontal scaling.

Vertical scaling

To increase or decrease the resources (CPU, memory) available to a Neo4j instance, change the neo4j.resources object in the values.yaml file to set the desired resource usage, and then perform a helm upgrade.

If you change the memory allocated to the Neo4j container, you should also change the Neo4j’s memory configuration (server.memory.heap.initial_size and server.memory.pagecache.size in particular). See Configure Resource Allocation for more details.

For example, if your running Neo4j instance has the following allocated resources:

# values.yaml
neo4j:
  resources:
    cpu: "1"
    memory: "3Gi"

# Neo4j Configuration (yaml format)
config:
  server.memory.heap.initial_size: "2G"
  server.memory.heap.initial_size: "2G"
  server.memory.pagecache.size: "500m"

And, you want to increase them to 2 CPUs and 4 GB of memory (allocating additional memory to the pagecache).

Modify the values.yaml file to set the desired resource usage:

# values.yaml
neo4j:
  resources:
    cpu: "2"
    memory: "4Gi"

# Neo4j Configuration (yaml format)
config:
  server.memory.heap.initial_size: "2G"
  server.memory.heap.initial_size: "2G"
  server.memory.pagecache.size: "1G"

Run helm upgrade with the modified deployment values.yaml file and the Neo4j Helm chart to apply the changes. For example:
```
helm upgrade <release-name> neo4j/neo4j -f values.yaml
```

Horizontal scaling

You can add a new server to the Neo4j cluster to scale out write or read workloads.

Example — add a new server to an existing cluster

The following example assumes that you have a cluster with 3 servers.

In the Kubernetes cluster, verify that you have a node that you can use for the new server, server4.
Install server4 using the same value for neo4j.name as your existing cluster:
```
helm install server4 neo4j --set neo4j.edition=enterprise --set neo4j.acceptLicenseAgreement=yes --set volumes.data.mode=defaultStorageClass --set neo4j.password="password" --set neo4j.minimumClusterSize=3 --set neo4j.name=my-cluster
```
Alternatively, you can use a values.yaml file to set the values for the new server and the neo4j/neo4j Helm chart to install the new server. For more information, see Create Helm deployment values files and Install Neo4j cluster servers.

When the new server joins the cluster, it will initially be in the Free state.

Enable server4 to be able to host databases by using cypher-shell (or Neo4j Browser) to connect to one of the existing servers:

Access the cypher-shell on server1:

kubectl exec -ti server1-0 -- cypher-shell -u neo4j -p password -d neo4j

When the cypher-shell prompt is ready, verify that server4 is in the Free state, and take a note of its name:

SHOW SERVERS;

+---------------------------------------------------------------------------------------------------------------------------------+
| name                                   | address                                | state     | health      | hosting             |
+---------------------------------------------------------------------------------------------------------------------------------+
| "0908819d-238a-473d-9877-5cc406050ea2" | "server4.neo4j.svc.cluster.local:7687" | "Free"    | "Available" | ["system"]          |
| "19817354-5cd1-4579-8c45-8b897808fdb4" | "server2.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
| "b3c91592-1806-41d0-9355-8fc6ba236043" | "server3.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
| "eefd7216-6096-46f5-9c41-a74f79684172" | "server1.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
+---------------------------------------------------------------------------------------------------------------------------------+

Using its name, enable server4 to use it in the cluster:
```
ENABLE SERVER "0908819d-238a-473d-9877-5cc406050ea2";
```

Run SHOW SERVERS; again to verify that server4 is enabled:

SHOW SERVERS;

+---------------------------------------------------------------------------------------------------------------------------------+
| name                                   | address                                | state     | health      | hosting             |
+---------------------------------------------------------------------------------------------------------------------------------+
| "0908819d-238a-473d-9877-5cc406050ea2" | "server4.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system"]          |
| "19817354-5cd1-4579-8c45-8b897808fdb4" | "server2.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
| "b3c91592-1806-41d0-9355-8fc6ba236043" | "server3.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
| "eefd7216-6096-46f5-9c41-a74f79684172" | "server1.neo4j.svc.cluster.local:7687" | "Enabled" | "Available" | ["system", "neo4j"] |
+---------------------------------------------------------------------------------------------------------------------------------+

Notice in the output that although server4 is now enabled, it is not hosting the neo4j database. You need to change the database topology to also use the new server.

Alter the neo4j database topology to be hosted on three primary and one secondary servers:
```
ALTER DATABASE neo4j SET TOPOLOGY 3 PRIMARIES 1 SECONDARY;
```

Now run the SHOW DATABASES; command to verify the new topology:

SHOW DATABASES;

+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| name     | type       | aliases | access       | address                                | role        | writer | requestedStatus | currentStatus | statusMessage | default | home  | constituents |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| "neo4j"  | "standard" | []      | "read-write" | "server2.neo4j.svc.cluster.local:7687" | "primary"   | TRUE   | "online"        | "online"      | ""            | TRUE    | TRUE  | []           |
| "neo4j"  | "standard" | []      | "read-write" | "server4.neo4j.svc.cluster.local:7687" | "secondary" | FALSE  | "online"        | "online"      | ""            | TRUE    | TRUE  | []           |
| "neo4j"  | "standard" | []      | "read-write" | "server3.neo4j.svc.cluster.local:7687" | "primary"   | FALSE  | "online"        | "online"      | ""            | TRUE    | TRUE  | []           |
| "neo4j"  | "standard" | []      | "read-write" | "server1.neo4j.svc.cluster.local:7687" | "primary"   | FALSE  | "online"        | "online"      | ""            | TRUE    | TRUE  | []           |
| "system" | "system"   | []      | "read-write" | "server2.neo4j.svc.cluster.local:7687" | "primary"   | FALSE  | "online"        | "online"      | ""            | FALSE   | FALSE | []           |
| "system" | "system"   | []      | "read-write" | "server4.neo4j.svc.cluster.local:7687" | "primary"   | FALSE  | "online"        | "online"      | ""            | FALSE   | FALSE | []           |
| "system" | "system"   | []      | "read-write" | "server3.neo4j.svc.cluster.local:7687" | "primary"   | TRUE   | "online"        | "online"      | ""            | FALSE   | FALSE | []           |
| "system" | "system"   | []      | "read-write" | "server1.neo4j.svc.cluster.local:7687" | "primary"   | FALSE  | "online"        | "online"      | ""            | FALSE   | FALSE | []           |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Note that server4 now hosts the neo4j database with the secondary role.

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