Do you know about Kubelet’s “syncFrequency”?

FoxuTech
3 min readDec 9, 2023

When a ConfigMap or Secret is updated, the Kubelet receives the most up-to-date contents of the object, but there is no mechanism to inform the Volume reconciliation logic to re-run when these resources are updated. Instead, the mounted volumes are only updated based on the Kubelet’s --sync-frequency flag or syncFrequency flag, which are set when starting the Kubelet. The default interval is one minute, which can cause delays when updates need to be reflected immediately.

Why kubelet checks ConfigMaps

Kubelet periodically checks ConfigMaps that are used by containers in Pods to ensure that the containers are running with the latest configuration data. This helps to keep your Kubernetes cluster healthy and stable.

Analogy:

Imagine driving a car. Before you start driving, it’s important to check the petrol/gas level to make sure you have enough fuel to reach your destination. Similarly, kubelet checks ConfigMaps to ensure that containers have the latest configuration data before they start running.

How often kubelet checks ConfigMaps

The frequency with which kubelet checks ConfigMaps is determined by the syncFrequency field in the KubeletConfiguration file. By default, syncFrequency is set to 1 minute, which means that kubelet checks ConfigMaps every 1 minute. If new changes are found to a ConfigMap, kubelet updates the running containers with the new changes.

When to change syncFrequency

The default value of syncFrequency is usually sufficient for most workloads. However, for workloads that change frequently, you may need to set syncFrequency to a lower value to ensure that containers are always running with the latest configuration data.

How to change syncFrequency

To change the syncFrequency value, follow these steps:

  • Edit the Kubelet Configuration file.

Add the following line to the file:

syncFrequency: 30s

Save the file and restart the kubelet service for the changes to take effect.

Additional considerations

Changing syncFrequency can impact kubelet performance. If you are not sure what value to use, it is best to consult with a Kubernetes expert.

If you are using ConfigMaps to store sensitive data, you should make sure that the data is encrypted and that the ConfigMap is mounted to Pods with appropriate permissions.

What are the benefits of checking ConfigMaps frequently?

Checking ConfigMaps frequently can help to ensure that your containers are always running with the latest configuration data. This can help to prevent problems such as:

  • Applications that are not running with the correct configuration
  • Applications that are not able to access the correct data.
  • Applications that are not able to communicate with each other properly.

What are the risks of checking ConfigMaps too frequently?

Checking ConfigMaps too frequently can put a strain on the kubelet and the API server. This can lead to performance problems, especially for large clusters.

In general, it is best to use the default syncFrequency value of one minute unless you have a specific need to change it.

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FoxuTech

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