# Health Check
ScyllaDB Manager automatically adds three health check tasks when the cluster is added to the ScyllaDB Manager and to existing clusters
during the upgrade procedure. You can see the tasks created by the healthcheck when you run
the [sctool tasks](https://manager.docs.scylladb.com/branch-3.9/sctool/task.md#task-list) command.
For example:
```none
sctool tasks -c prod-cluster
```
returns:
```none
sctool tasks -c prod-cluster
╭────────────────────────┬──────────────┬────────┬──────────────────┬─────────┬───────┬──────────────┬────────────┬─────────┬────────────────╮
│ Task │ Schedule │ Window │ Timezone │ Success │ Error │ Last Success │ Last Error │ Status │ Next │
├────────────────────────┼──────────────┼────────┼──────────────────┼─────────┼───────┼──────────────┼────────────┼─────────┼────────────────┤
│ healthcheck/cql │ @every 15s │ │ America/New_York │ 4 │ 0 │ 1s ago │ │ DONE │ in 13s │
│ healthcheck/alternator │ @every 15s │ │ America/New_York │ 3 │ 0 │ 14s ago │ │ RUNNING │ │
│ healthcheck/rest │ @every 1m0s │ │ America/New_York │ 1 │ 0 │ 1s ago │ │ DONE │ in 58s │
│ repair/all-weekly │ 0 23 * * SAT │ │ America/New_York │ 0 │ 0 │ │ │ NEW │ in 2d13h30m55s │
╰────────────────────────┴──────────────┴────────┴──────────────────┴─────────┴───────┴──────────────┴────────────┴─────────┴────────────────╯
```
We can see three healthcheck related tasks:
* Healthcheck - which checks the ScyllaDB CQL, repeating every 15 seconds.
* Healthcheck Alternator - which checks the ScyllaDB Alternator API, repeating every 15 seconds.
* Healthcheck REST - which checks the ScyllaDB REST API, repeating every minute.
## ScyllaDB Health Check
The ScyllaDB health check task ensures that CQL native port is accessible on all the nodes.
ScyllaDB Manager reads CQL IP address and port from the node configuration, and can automatically detect TLS/SSL connection.
There are two types of CQL health check [Credentials agnostic health check](#credentials-agnostic-health-check) and [CQL query health check](#cql-query-health-check).
The results are available using the [sctool status](https://manager.docs.scylladb.com/branch-3.9/sctool/status.md#id1) command.
For example:
```none
sctool status -c prod-cluster
Datacenter: eu-west
╭────┬────────────┬───────────┬───────────┬───────────────┬──────────┬──────┬──────────┬────────┬──────────┬──────────────────────────────────────╮
│ │ Alternator │ CQL │ REST │ Address │ Uptime │ CPUs │ Memory │ Scylla │ Agent │ Host ID │
├────┼────────────┼───────────┼───────────┼───────────────┼──────────┼──────┼──────────┼────────┼──────────┼──────────────────────────────────────┤
│ UN │ UP (4ms) │ UP (3ms) │ UP (2ms) │ 34.203.122.52 │ 237h2m1s │ 4 │ 15.43GiB │ 4.1.0 │ 2.2.0 │ 8bfd18f1-ac3b-4694-bcba-30bc272554df │
│ UN │ UP (15ms) │ UP (11ms) │ UP (12ms) │ 10.0.138.46 │ 237h2m1s │ 4 │ 15.43GiB │ 4.1.0 │ 2.2.0 │ 238acd01-813c-4c55-bd65-5219bb19bc20 │
│ UN │ UP (17ms) │ UP (5ms) │ UP (7ms) │ 10.0.196.204 │ 237h2m1s │ 4 │ 15.43GiB │ 4.1.0 │ 2.2.0 │ bde4581a-b25e-49fc-8cd9-1651d7683f80 │
│ UN │ UP (10ms) │ UP (4ms) │ UP (5ms) │ 10.0.66.115 │ 237h2m1s │ 4 │ 15.43GiB │ 4.1.0 │ 2.2.0 │ 918a52aa-cc42-43a4-a499-f7b1ccb53b18 │
╰────┴────────────┴───────────┴───────────┴───────────────┴──────────┴──────┴──────────┴────────┴──────────┴──────────────────────────────────────╯
```
The status information is also available as a metric in ScyllaDB Monitoring Manager dashboard.
The healthcheck task checks nodes every 15 seconds, the interval can be changed using `task-update` command.
The CQL column shows the CQL status, SSL indicator if SSL is enabled on a node, and time the check took.
Available statuses are:
* UP - Situation normal
* DOWN - Failed to connect to host or CQL error
* ERROR - Precondition failure, no request was sent
* UNAUTHORISED - Wrong username or password - only if `username` is specified for cluster
* TIMEOUT - Timeout
The REST column shows the status of ScyllaDB Manager Server to ScyllaDB API communication, and time the check took.
Available statuses are:
* UP - Situation normal
* DOWN - Failed to connect to host
* ERROR - Precondition failure, no request was sent
* HTTP XXX - HTTP failure and its status code
* UNAUTHORISED - Missing or Incorrect [Authentication Token](https://manager.docs.scylladb.com/branch-3.9/install-scylla-manager-agent.md#configure-auth-token) was used
* TIMEOUT - Timeout
## Error information
#### Versionadded
Added in version 2.5: ScyllaDB Manager
In case of error (status ERROR or DOWN) there is additional error section below the table describing the errors.
```none
sctool status -c test-cluster
Datacenter: eu-west
╭────┬────────────┬────────────┬──────────┬────────────────┬──────────┬──────┬──────────┬────────┬──────────┬──────────────────────────────────────╮
│ │ Alternator │ CQL │ REST │ Address │ Uptime │ CPUs │ Memory │ Scylla │ Agent │ Host ID │
├────┼────────────┼────────────┼──────────┼────────────────┼──────────┼──────┼──────────┼────────┼──────────┼──────────────────────────────────────┤
│ UN │ UP (12ms) │ DOWN (0ms) │ UP (3ms) │ 192.168.100.11 │ 1h32m35s │ 4 │ 31.11GiB │ 4.2.1 │ 2.5.0 │ 1edbfd5b-4b1c-4bb0-afab-d69fd25db6af │
│ UN │ UP (8ms) │ UP (3ms) │ UP (5ms) │ 192.168.100.12 │ 1h32m35s │ 4 │ 31.11GiB │ 4.2.1 │ 2.5.0 │ 0c0999a2-c879-4e69-9924-1641c8487bd5 │
│ UN │ UP (10ms) │ UP (8ms) │ UP (1ms) │ 192.168.100.13 │ 1h32m35s │ 4 │ 31.11GiB │ 4.2.1 │ 2.5.0 │ 73e9818e-ed8d-4ea8-89e4-cf485dfd4ebe │
╰────┴────────────┴────────────┴──────────┴────────────────┴──────────┴──────┴──────────┴────────┴──────────┴──────────────────────────────────────╯
Errors:
- 192.168.100.11 CQL: dial tcp 192.168.100.11:9042: connect: connection refused
```
## Node information
#### Versionadded
Added in version 2.2: ScyllaDB Manager
Node status check also provides additional columns that show properties of the available nodes. Those are:
- CPUs - Total OS CPU count
- Memory - Total OS memory available
- Uptime - How long the system has been running without restarts
- ScyllaDB - Version of ScyllaDB server running on the node
- Agent - Version of ScyllaDB Manager Agent running on the node
- Host - UUID of the node
- Address - IP address of the node
## ScyllaDB Monitoring
If you have enabled the ScyllaDB Monitoring stack, ScyllaDB Manager dashboard includes the same cluster status report.
In addition, the Prometheus Alert Manager has an alert to report when a ScyllaDB node health check fails.
## Credentials agnostic health check
ScyllaDB Manager does not require database credentials to work.
CQL health check is based on sending [CQL OPTIONS frame](https://github.com/apache/cassandra/blob/trunk/doc/native_protocol_v4.spec#L302) 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 :ref: \`.
## CQL query health check
#### Versionadded
Added in version 2.2: ScyllaDB Manager
You may specify CQL `username` and `password` flags when adding cluster to ScyllaDB Manager using [sctool cluster add](https://manager.docs.scylladb.com/branch-3.9/sctool/cluster.md#cluster-add) command.
It’s also possible to add or change that using [sctool cluster update](https://manager.docs.scylladb.com/branch-3.9/sctool/cluster.md#cluster-update) command.
Once ScyllaDB 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 WHERE key='local'` query.
## ScyllaDB Alternator Health Check
#### Versionadded
Added in version 2.2: ScyllaDB Manager
If Alternator is enabled it will check the ScyllaDB Alternator API connectivity for all nodes in parallel. In ScyllaDB 4.0, it uses simplified ping checking if the socket is open and if it’s responding. In ScyllaDB 4.1+, it queries the system table.
Please check the ScyllaDB Manager [ScyllaDB Manager Config](https://manager.docs.scylladb.com/branch-3.9/config/scylla-manager-config.md#configuration-file) to adjust timeouts for your cluster.
## ScyllaDB REST API Health Check
Checks ScyllaDB REST API connectivity by performing single HTTP request-response cycle between ScyllaDB Manager Server and all ScyllaDB nodes in parallel.
Please check the ScyllaDB Manager [ScyllaDB Manager Config](https://manager.docs.scylladb.com/branch-3.9/config/scylla-manager-config.md#configuration-file) to adjust timeouts for your cluster.