<a id="ksqldb-install-check-server-health"></a>

# Check the Health of a ksqlDB Server in ksqlDB for Confluent Platform

## Check a ksqlDB Server from the ksqlDB CLI

Check the streams, tables, and queries on the ksqlDB Server that you’re
connected to by using the DESCRIBE EXTENDED and EXPLAIN statements in
the ksqlDB CLI.

- Run SHOW STREAMS or SHOW TABLES, then run
  `DESCRIBE <stream|table> EXTENDED`.
- Run SHOW QUERIES, then run `EXPLAIN <query-name>`.

## Check a ksqlDB Server running in a native deployment

If you installed ksqlDB server by using a package manager, like a DEB or
RPM, or from an archive, like a TAR or ZIP file, you can check the
health of your ksqlDB Server instances by using shell commands.

### Check the ksqlDB Server process status

Use the `ps` command to check whether the ksqlDB Server process is
running:

```bash
ps -aux | grep ksql
```

Your output should resemble:

```text
jim       2540  5.2  2.3 8923244 387388 tty2   Sl   07:48   0:33 /usr/lib/jvm/java-8-oracle/bin/java -cp ...
```

If the process status of the JVM isn’t `Sl` or `Ssl`, the ksqlDB
server may be down.

## Check a ksqlDB Server by using the REST API

The ksqlDB REST API supports a “server info” request, which you access
with a URL like `http://<ksqldb-server-host>/info`. The `/info`
endpoint returns the ksqlDB Server version, the Apache Kafka® cluster
ID, and the service ID of the ksqlDB Server.

Also, the ksqlDB REST API supports a basic health check endpoint at
`/healthcheck`.

#### IMPORTANT
This approach doesn’t work for non-interactive, or *headless*, deployments
of ksqlDB Server, because a headless deployment doesn’t have a REST API
server. Instead, check the
[JMX metrics port](#ksqldb-install-check-server-health-jmx-metrics-port).

For more information, see
[Introspect server status](../../developer-guide/ksqldb-rest-api/info-endpoint.md#ksqldb-rest-api-info-endpoint).

## Check a ksqlDB Server running in a Docker container

If you’re running ksqlDB server in a Docker container, run the
`docker ps` or `docker-compose ps` command, and check that the
status of the `ksql-server` container is `Up`. Check the health of
the process in the container by running
`docker logs <ksql-server-container-id>`.

<a id="ksqldb-install-check-server-health-jmx-metrics-port"></a>

## Check the JMX metrics port

In addition to the previous health checks, you can query the Java
Management Extensions (JMX) port on a host that runs ksqlDB Server.

This is useful when you need to check a headless ksqlDB Server that’s
running natively or in a Docker container, because headless deployments
of ksqlDB Server don’t have a REST server that you can query for health.
Instead, you can probe the JMX port for liveness. A JMX probe is the
most reliable way to determine readiness of a headless deployment.

#### NOTE
JMX indicates that the JVM is up and responsive. This test is similar to
confirming if the ksqlDB process is running, but a successful response
doesn’t necessarily mean that the ksqlDB service is fully operational.
To get better exposure, you can monitor the nodes from Confluent Control Center or JMX.

The following command probes the JMX port by using the Netcat utility.

```bash
nc -z <ksql-node>:1099
```

An exit code of 0 for an open port tells you that the container and
ksqlDB JVM are running. This confirmation has a level of confidence
that’s similar to the REST health check.

The general responsiveness on the port should be sufficient as a
high-level health check. For a list of the available metrics you can
collect, see [JMX Metrics](../../reference/metrics.md#ksqldb-reference-metrics).