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:

ps -aux | grep ksql

Your output should resemble:

jim       2540  5.2  2.3 8923244 387388 tty2   Sl   07:48   0:33 /usr/lib/jvm/java-8-oracle/bin/java -cp /home/jim/confluent-0.29.0/share/java/monitoring-interceptors/* ...

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.

For more information, see Introspect server status.

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>.

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.

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.