Health Check

The health check ensures that CQL and Scylla API work across the cluster. The health check results are available using the sctool status command.

sctool status
Cluster: prod-cluster (c1bbabf3-cad1-4a59-ab8f-84e2a73b623f)
Datacenter: eu-west
╭────┬───────────────┬────────────┬──────────────┬──────────────────────────────────────╮
│    │ CQL           │ REST       │ Host         │ Host ID                              │
├────┼───────────────┼────────────┼──────────────┼──────────────────────────────────────┤
│ UN │ UP SSL (42ms) │ UP (52ms)  │ 10.0.114.68  │ 45a7390d-d162-4daa-8bff-6469c9956f8b │
│ UN │ UP SSL (38ms) │ UP (88ms)  │ 10.0.138.46  │ 8dad7fc7-5a82-4fbb-8901-f6f60c12342a │
│ UN │ UP SSL (38ms) │ UP (298ms) │ 10.0.196.204 │ 44eebe5b-e0cb-4e45-961f-4ad175592977 │
│ UN │ UP SSL (43ms) │ UP (159ms) │ 10.0.66.115  │ 918a52aa-cc42-43a4-a499-f7b1ccb53b18 │
╰────┴───────────────┴────────────┴──────────────┴──────────────────────────────────────╯

If you have enabled the Scylla Monitoring stack, Scylla Manager dashboard includes the same cluster status report. In addition, the Prometheus Alert Manager has an alert to report when a Scylla node health check fails.

Scylla Manager just works! It reads CQL IP address and port from node configuration, and can automatically detect TLS/SSL connection. There are two types of CQL health check Credentials agnostic health check and CQL query health check.

Credentials agnostic health check

Scylla Manager does not require database credentials to work. CQL health check is based on sending CQL OPTIONS frame and does not start a CQL session. This is simple and effective but does not test CQL all the way down. For that you may consider upgrading to CQL query health check.

CQL query health check

You may specify CQL username and password flags when adding cluster to Scylla Manager using sctool cluster add command. It’s also possible to add or change that using sctool cluster update command. Once Scylla Manager has CQL credential to the cluster, when performing a health check, it would try to connect to each node and execute SELECT now() FROM system.local query.