Kubernetes Default Ephemeral Storage

Kubernetes has become the de facto standard for container orchestration in modern cloud - native applications. One of the key aspects of running applications in Kubernetes is storage management. Ephemeral storage in Kubernetes plays a crucial role in providing a short - lived and local storage space for containers. This blog post will delve into the details of Kubernetes default ephemeral storage, including its core concepts, typical usage examples, common practices, and best practices.

Table of Contents

  1. Core Concepts
  2. Typical Usage Example
  3. Common Practices
  4. Best Practices
  5. Conclusion
  6. References

Core Concepts

What is Ephemeral Storage?

Ephemeral storage in Kubernetes is a type of storage that is local to a node and is associated with a pod. It is designed to store non - persistent data such as scratch space, caching, and logs. Unlike persistent volumes, ephemeral storage does not survive the deletion of a pod.

Default Ephemeral Storage

Kubernetes provides a default ephemeral storage for each pod. This storage is allocated from the node’s local storage. The amount of default ephemeral storage available to a pod can be configured using resource requests and limits.

Resource Requests and Limits

  • Requests: A pod can request a certain amount of default ephemeral storage. This is a guarantee that the scheduler will use to ensure that the node has enough available storage when scheduling the pod. For example, if a pod requests 100Mi of default ephemeral storage, the scheduler will only place the pod on a node that has at least 100Mi of available ephemeral storage.
  • Limits: A limit can be set on the amount of default ephemeral storage a pod can use. If a pod tries to use more storage than its limit, it may be evicted by the kubelet.

Typical Usage Example

Pod Definition with Ephemeral Storage

apiVersion: v1
kind: Pod
metadata:
  name: ephemeral - storage - example
spec:
  containers:
  - name: main - container
    image: nginx
    resources:
      requests:
        ephemeral - storage: "200Mi"
      limits:
        ephemeral - storage: "500Mi"

In this example, the main - container in the ephemeral - storage - example pod requests 200Mi of default ephemeral storage and has a limit of 500Mi.

How the Container Uses Ephemeral Storage

Inside the container, the default ephemeral storage is typically available at the /var/lib/kubelet/pods/<pod - uid>/volumes/kubernetes.io~empty-dir/default - ephemeral - storage directory. The container can use this directory to store temporary files, logs, or cache data.

Common Practices

Monitoring Ephemeral Storage Usage

It is important to monitor the ephemeral storage usage of pods. Tools like Prometheus and Grafana can be used to collect and visualize ephemeral storage metrics. You can use the container_fs_usage_bytes metric to monitor the actual storage usage of containers.

Handling Logs

Since logs are a common use case for ephemeral storage, it is important to manage them properly. You can configure log rotation in your containers to prevent logs from consuming too much ephemeral storage. For example, in a Node.js application, you can use a library like winston to implement log rotation.

Cleaning Up Temporary Files

Containers should be designed to clean up temporary files regularly. This can be done by implementing a script that runs periodically to delete old files from the ephemeral storage directory.

Best Practices

Set Appropriate Requests and Limits

Carefully estimate the amount of ephemeral storage your application needs and set appropriate requests and limits. Setting a too - low limit may cause pods to be evicted frequently, while setting a too - high limit may waste node resources.

Use Ephemeral Volumes for Specific Needs

If your application has specific ephemeral storage requirements, consider using ephemeral volumes like emptyDir or projected instead of relying solely on the default ephemeral storage. emptyDir volumes can be customized for each pod, allowing you to have more control over the storage space.

Plan for Node Storage Capacity

When deploying pods with ephemeral storage requirements, consider the overall storage capacity of the nodes. Ensure that your cluster has enough nodes with sufficient storage to accommodate the ephemeral storage needs of all pods.

Conclusion

Kubernetes default ephemeral storage is a valuable resource for storing non - persistent data in pods. By understanding its core concepts, using it in typical scenarios, following common practices, and adhering to best practices, intermediate - to - advanced software engineers can effectively manage ephemeral storage in their Kubernetes clusters. This not only ensures the smooth running of applications but also optimizes the use of node resources.

References