Stateful containers are becoming a hot topic these days so we thought it a good time to talk to the CNCF (Cloud Native Computing Foundation) Rook team about what they are doing to make storage easier to use for k8s container apps. CNCF put us into contact with Sébastien Han (@leseb_), Ceph Storage Architect and Travis Nielsen (@STravisNielsen), both Principal Software Engineers at Red Hat and active on the Rook project. Rook is a CNCF “graduated” open source project just like Kubernetes, Prometheus, ContainerD, etc., this means it’s mature enough to run production workloads.
Rook is used to configure, deploy and manage a Red Hat Ceph(r) Storage cluster under k8s. Rook creates all the k8s deployment scripts to set up a Ceph Storage cluster as containers, start it and monitor its activities. Rook monitoring of Ceph operations can restart any Ceph service container or scale any Ceph services up/down as needed by container apps using its storage. Rook is not in the Ceph data path, but rather provides a k8s based Ceph control or management plane for running Ceph storage under k8s.
Readers may recall we talked to SoftIron, an appliance provider, for Ceph Storage in the enterprise for our 120th episode. Rook has another take on using Ceph storage, only this time running it under k8s,. Listen to the podcast to learn more.
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The main problem Rook is solving is how to easily incorporate storage services and stateful container apps within k8s control. Containerized apps can scale up or down based on activity and storage these apps use needs the same capabilities. The other option is to have storage that stands apart or outside k8s cluster and control. But then tho container apps and their storage have 2 (maybe more) different control environments. Better to have everything under k8s control or nothing at all.
Red Hat Ceph storage has been available as a standalone storage solutions for a long time now and has quite the extensive customer list, many with multiple PB of storage. Rook-Ceph and all of its components run as containers underneath k8s.
Ceph supports replication (mirroring) of data 1 to N ways typically 3 way or erasure coding for data protection and also supports file, block and object protocols or access methods. Ceph normally consumes raw block DAS for it’s backend but Ceph can also support a file gateway to NFS storage behind it. Similarly, Ceph can offers an object storage gateway option. But with either of these approaches, the (NFS or object) storage exists outside k8s scaling and resiliency capabilities and Rook management.
Ceph uses storage pools that can be defined using storage performance levels, storage data protection levels, system affinity, or any combination of the above. Ceph storage pools are mapped to k8s storage classes using the Ceph CSI. Container apps that want to use storage would issue a persistent volume claim (PVC) request specifying a Ceph storage class which would allocate the Ceph storage from the pool to the container.
Besides configuring, deploying and monitoring/managing your Ceph storage cluster, Rook can also automatically upgrade your Ceph cluster for you.
We discussed the difference between running Rook-Ceph within k8s and running Ceph outside k8s. Both approaches depend on Ceph CSI but with Rook, Ceph and all its software is all running under k8s control as containers and Rook manages the Ceph cluster for you. When it’s run outside 1) you manage the Ceph cluster and 2) Ceph storage scaling and resilience are not automatic.
Sébastien Han, Principal Software Engineer, Ceph Architect, Red Hat
Sebastien Han currently serves as a Senior Principal Software Engineer, Storage Architect for Red Hat. He has been involved with Ceph Storage since 2011 and has built strong expertise around it.
Curious and passionate, he loves working on bleeding edge technologies and identifying opportunities where Ceph can enhance the user experience. He did that with various technology such as OpenStack, Docker.
Now on a daily basis, he rotates between Ceph, Kubernetes, and Rook in an effort to strengthen the integration between all three. He is one of the maintainers of Rook-Ceph.
Travis Nielson, Principal Software Engineer, Red Hat
Travis Nielsen is a Senior Principal Software Engineer at Red Hat with the Ceph distributed storage system team. Travis leads the Rook project and is one of the original maintainers, integrating Ceph storage with Kubernetes.
Prior to Rook, Travis was the storage platform tech lead at Symform, a P2P storage startup, and an engineering lead for the Windows Server group at Microsoft.