Before restarting Kafka servers, ensure the process is smooth to avoid data loss or service interruptions. Below are the steps for restarting Kafka servers:
1. Plan the Restart Time
First, choose a period with low traffic for the restart to minimize impact on business operations. Notify relevant teams and service users about the scheduled restart time and expected maintenance window.
2. Verify Cluster Status
Before restarting, verify the status of the Kafka cluster. Use command-line tools such as kafka-topics --describe to check the status of all replicas and ensure all replicas are in sync.
kafka-topics --zookeeper zookeeper-server:port --describe --topic your-topic-name
Ensure the ISR (In-Sync Replicas) list includes all replicas.
3. Perform Safe Backups
Although Kafka is designed with high availability in mind, it is still a good practice to back up data before performing a restart. This can be done through physical backups (e.g., using disk snapshots) or by using tools like MirrorMaker to back up data to another cluster.
4. Gradually Stop Producers and Consumers
Before restarting, gradually scale down the number of producers sending messages to Kafka while also gradually stopping consumers. This can be achieved by progressively reducing client traffic or directly stopping client services.
5. Stop Kafka Service
On a single server, use the appropriate command to stop the Kafka service. For example, if using systemd, the command might be:
sudo systemctl stop kafka
If using a custom script, it might be:
/path/to/kafka/bin/kafka-server-stop.sh
6. Restart the Server
Restart the physical server or virtual machine. This is typically done using the standard reboot command of the operating system:
sudo reboot
7. Start Kafka Service
After the server restarts, restart the Kafka service. Similarly, if using systemd:
sudo systemctl start kafka
Or use the Kafka-provided startup script:
/path/to/kafka/bin/kafka-server-start.sh /path/to/kafka/config/server.properties
8. Verify Service Status
After the restart is complete, check the Kafka log files to ensure there are no error messages. Use the command-line tools mentioned earlier to verify that all replicas have recovered and are in sync.
9. Gradually Resume Producers and Consumers
Once confirmed that Kafka is running normally, gradually resume producers and consumers to normal operation.
Example
For example, in a Kafka cluster with three nodes, if we need to restart Node 1, we will follow the above steps to stop the service on Node 1, restart the machine, and then restart the service. During this process, we monitor the cluster status to ensure the remaining two nodes can handle all requests until Node 1 fully recovers and rejoins the cluster.
By following these steps, we can ensure that the Kafka server restart process is both safe and effective, minimizing the impact on business operations.