Prerequisites
AxonOps Server requires a primary datastore: Elasticsearch or
OpenSearch. This is the main datastore for AxonOps — it holds logs,
configuration, events, alerts, dashboards, and, by default, the metrics collected
from monitored Apache Cassandra and Apache Kafka clusters. It is configured via
elastic_hosts / search_db in axon-server.yml and is always required.
For larger deployments, a dedicated Apache Cassandra cluster can be added as
the metrics storage engine. Cassandra then stores only the high-volume
metrics (configured via cql_hosts), while Elasticsearch or OpenSearch continues
to store everything else.
In summary:
- Elasticsearch or OpenSearch — always required (the primary datastore).
- Apache Cassandra — optional, stores only metrics, for larger deployments.
Where to store metrics
Section titled “Where to store metrics”By default, metrics are stored in the Elasticsearch/OpenSearch primary datastore. Whether to offload them to a dedicated Cassandra cluster depends on the size of the deployment being monitored:
| Monitored nodes | Metrics storage |
|---|---|
| Up to 8 | Elasticsearch / OpenSearch (the primary datastore) — no separate metrics database needed |
| More than 8 | A dedicated Apache Cassandra cluster, in addition to Elasticsearch / OpenSearch |
- For small deployments (up to 8 monitored nodes), storing metrics in Elasticsearch or OpenSearch is sufficient — a single node is adequate and no separate Cassandra cluster is required.
- For larger deployments (more than 8 monitored nodes), a dedicated Apache Cassandra cluster should be added to store the metrics. Cassandra scales horizontally and sustains the higher write throughput and retention that larger fleets generate. Elasticsearch or OpenSearch is still required for logs, configuration, and everything else.
Note
The threshold is a guideline, not a hard limit. Retention period, metrics resolution, and the number of monitored tables/topics also affect storage load. Deployments near the boundary, or with long retention requirements, should add Cassandra for metrics.
Database requirements
Section titled “Database requirements”Elasticsearch or OpenSearch (required)
Section titled “Elasticsearch or OpenSearch (required)”- The primary datastore: logs, configuration, events, dashboards, and metrics.
- A single node is sufficient for small deployments.
- Requires tuning of heap size, memory maps, file descriptors, and the bulk queue (covered on the install pages).
- Basic authentication (Elasticsearch) or the security plugin (OpenSearch) is recommended; AxonOps connects with a dedicated user and role.
Apache Cassandra (optional — metrics only, at scale)
Section titled “Apache Cassandra (optional — metrics only, at scale)”- A dedicated cluster, separate from any monitored cluster.
- At least 3 nodes are recommended.
- Stores only metrics; Elasticsearch or OpenSearch is still required.
- AxonOps Server creates the required keyspace and tables by default.
Next steps
Section titled “Next steps”Install the Elasticsearch or OpenSearch primary datastore, optionally add Cassandra for metrics, then continue with the AxonOps Server installation: