kube-arangodb/docs/scaling.md

Scaling your ArangoDB deployment

The ArangoDB Kubernetes Operator allows easily scale the number of DB-Servers and Coordinators up or down as needed.

The scale up or down, change the number of servers in the custom resource.

E.g., change spec.dbservers.count from 3 to 4.

Then apply the updated resource using:

kubectl apply -f {your-arango-deployment}.yaml

Inspect the status of the custom resource to monitor the progress of the scaling operation.

Note: It is not possible to change the number of Agency servers after creating a cluster. Make sure to specify the desired number when creating CR first time.

Overview

Scale-up

When increasing the count, operator will try to create missing pods. When scaling up, make sure that you have enough computational resources / nodes, otherwise pod will be stuck in Pending state.

Scale-down

Scaling down is always done one server at a time.

Scale down is possible only when all other actions on ArangoDeployment are finished.

The internal process followed by the ArangoDB operator when scaling down is as follows:

• It chooses a member to be evicted. First, it will try to remove unhealthy members or fall-back to the member with the highest deletion_priority (check Use deletion_priority to control scale-down order).
• Making an internal calls, it forces the server to resign leadership. In case of DB servers it means that all shard leaders will be switched to other servers.
• Wait until server is cleaned out from the cluster.
• Pod finalized.

Use deletion_priority to control scale-down order

You can use .spec.deletion_priority field in ArangoMember CR to control the order in which servers are scaled down. Refer to ArangoMember API Reference for more details.