Kubernetes storage solutions integrate with Kubernetes to enable stateful storage. Kubernetes is an open source container orchestrator. It is highly dynamic, creating and deleting containers and pods as needed. This level of scalability is possible because containers and pods are ephemeral. However, you cannot tie stateful storage to ephemeral resources.
Kubernetes storage architecture utilizes volumes as a central abstraction. The platform lets you use persistent and non-persistent, letting containers request storage resources dynamically through volume claims. This basic mechanism does not allow easy storage management. Open source Kubernetes storage solutions, like OpenEBS, Rook, GlusterFS, and LongHorn, provide the capabilities needed to effectively manage persistent storage for Kubernetes applications.
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Why Is Storage on Kubernetes So Complex?
Kubernetes offers scalability, efficient management, and portability but does not support storing state. Kubernetes is highly dynamic, constantly creating and destroying containers according to the load and predefined specifications. Additionally, containers and pods are ephemeral and can replicate and self-heal.
Since most production applications are stateful, they require external storage. However, persistent storage solutions cannot work with Kubernetes’s dynamic behavior that dynamically creates and destroys pods and containers. As a result, stateful applications need to handle portability challenges, for example, deciding when deploying the application on another infrastructure, such as clouds, on-premises, or hybrid environments.
While you can tie persistent storage solutions to specific cloud providers, the cloud native application storage landscape can be difficult to navigate. Kubernetes storage terms are often confusing, with many terms including intricate meanings or subtle changes. There are also many options, such as native Kubernetes, managed or paid services, and open-source frameworks that further complicate storage decisions.
Related content: Read our guide to Kubernetes multi tenancy
Top Open Source Kubernetes Storage Solutions
1. OpenEBS
License: Apache License
GitHub Repo: https://github.com/openebs/openebs
OpenEBS is an open source project that provides cloud native storage solutions for Kubernetes. Unlike other solutions, OpenEBS easily integrates with Kubernetes, making it a popular solution. It offers container-native storage employing Kubernetes to store and manage data, using container-attached storage (CAS) architecture.
The CAS architecture ensures every storage volume has its own dedicated pod and set of replica pods deployed and managed like other containers or microservices in Kubernetes. You can also deploy OpenEBS as a container to easily assign storage services on the container, application, or cluster level.
The project supports synchronous replication to allow replicating data volumes across different availability zones to achieve high availability. You can use this feature to build a highly available stateful application that uses local disks on cloud services like Google Kubernetes Engine (GKE).
A key advantage of OpenEBS is that it helps avoid vendor lock-in issues that occur due to the differences in storage architecture implementations by each cloud provider. OpenEBS solves this by defining a layer of abstraction between the applications and the supporting cloud service provider. It makes migrating data across multiple providers easier—there’s no need to handle the underlying architecture.
2. Rook
License: Apache License
GitHub Repo: https://github.com/rook/rook
Rook is an open source project supported by the Cloud Native Computing Foundation (CNCF). This cloud native solution is a community-driven endeavor to help manage block, object, and file storage. It lets you choose from various storage providers while providing a framework, platform, and user support.
Ceph Rook is considered the most stable version, providing highly-scalable distributed storage. Rook lets you use YAML files to declare the desired number of variables needed in the cluster. Next, it spins up clusters and checks in as an admin controller to ensure the defined config file runs as intended.
Rook lets you introduce storage providers on Kubernetes using the kubectl command. Once deployed, the solution lets you easily manage your application’s shared file systems or storage operations. It stores data as block objects built using a StorageClass and automatically mounts storage units onto pods using CephBlockPool.
Rook lets you scale, secure, and manage cluster resources from one place. It provides a dashboard for storage clusters that lets you check cluster health and resource status. Additionally, it supports monitoring through third-party tools like Grafana and Prometheus so that you can manage advanced metrics, graphs, and alerts for storage containers.
3. GlusterFS
License: GPLV2 and LGPLV3+
GitHub Repo: https://github.com/gluster/glusterfs
GlusterFS is an open source network filesystem solution backed by RedHat that offers an open source (community) version and a commercial version. The solution aggregates data storage from various sources into scalable, distributed file systems.
It provides a RESTful interface to manage volumes, called Heketi, that lets you automate Kubernetes volume provisioning. This feature eliminates the overhead of manually mapping and creating GlusterFS volumes to Kubernetes persistent volumes.
GlusterFS is not a Kubernetes-native storage solution. Rather, it provides a storage solution that can work with Kubernetes. The Heketi interface supports Kubernetes integration but is a relatively new addition and only updated after users encounter significant bugs.
4. Longhorn
License: Apache License
GitHub Repo: https://github.com/longhorn/longhorn
LongHorn is an open source framework that offers distributed lightweight block storage for Kubernetes. It works by separating block storage into multiple LongHorn volumes to enable using Kubernetes volumes separately or with a cloud provider. It uses containers and microservices to implement distributed block storage.
LongHorn can replicate block storage over several data centers and nodes to help improve availability. It also supports non-disruptive, automated upgrades to ensure you can upgrade the whole LongHorn stack without disrupting the running volumes.
You can use LongHorn to schedule automated recurring backups to secondary or external locations like AWS S3 or NFS. It also lets you recover data from your primary Kubernetes cluster using cross-cluster recovery volumes in other Kubernetes clusters.
LongHorn features include RWX storage with high availability, storage networking support, and an advanced API. The last version release introduced support for volume and backup encryption, backup policy rules, automatic rebalancing of replicas, and volume cloning.
What Should You Look for in a Kubernetes Storage Provider?
Kubernetes enables you to avoid vendor lock-in. All major cloud providers support Kubernetes, and you can also manage clusters across multi-cloud environments. However, this setup requires a highly portable storage solution that supports deployment on local hardware and in the cloud.
Scaling is also a crucial aspect to consider in a Kubernetes storage solution. Ideally, the storage solution should be highly available and performant, with the ability to scale up or down to meet the changing demands of your highly dynamic system. This way, if a node needs an update or is lost, it can recover thoroughly and quickly.
Additionally, your Kubernetes storage solution must integrate smoothly with the existing monitoring solutions. Observing the environment’s performance is a core component of any system, and a storage solution works as an integral part of the system.
Scalable Kubernetes Storage with Cloudian
Containerized applications require storage that’s agile and scalable. The Cloudian Kubernetes S3 Operator lets you access exabyte-scalable Cloudian storage from your Kubernetes-based applications. Built on the S3 API, Cloudian lets you dynamically or statically provision object storage with this lightweight Operator using S3 APIs. You get cloud-like storage access in your own data center.
Cloudian’s key features for Kubernetes storage include:
- S3 API for Application Portability—eliminates lock-in and enhances application portability. Provides fast, self-serve storage access using the standard Kubernetes Persistent Volume (PV) and Persistent Volume Claim (PVC) methodology to provision assets.
- Multi-tenancy for Shared Storage—lets you create separate namespaces and self-serve management environments for development and production users. Each tenant’s environment is isolated, with data invisible to other tenants. Performance can be managed with integrated quality of services (QoS) controls.
- Hybrid Cloud-Enabled—males it easy to replicate or migrate data to AWS, GCP, or Azure. Data stored to the cloud is always stored in that cloud’s native format, meaning it’s directly accessible to cloud-based applications, with no lock-in.