This project implements a simple storage solution for kubernetes. it is based on DRBD (distribute replication block device) open source software, which is natively data redundancy and high performance.
We asumed that you have all your kubernetes nodes installed lvm-utils and at least DRBD 9.0 (userspace utils and kernel module). For more about DRBD, please refer to LINBIT.
Userspace Apps filesystem operations get replicated to another disk on the network node, the whole process is transparent and high performance. Apps can be migrated to that secondary node quickly and seamlessly with data already have been placed right there.
DRBD Primary DRBD Secondary
+-----------------------+ +----------------------+
| Userspace | | Userspace |
| | | |
| open/read/write/close | | |
+--------------|--------+ +----------------------+
| Kernel | | tcp/ip | Kernel |
| +----------->---->---->--------------+ |
| | | | | |
+--------------v--------+ +-----------v----------+
| Disk: /dev/drbd0 | | Disk: /dev/drbd0 |
+-----------------------+ +----------------------+
Kubernetes is good at stateless Pod migration, but this is not true as to satefull Pod. So here DRBD comes to play.
- Pod mysql runs on k8s-node-1
k8s-node-1 k8s-node-2
+--------------------------+ +---------------------------+
| Kubelet: drbd flexvolume | | Kubelete: drbd flexvolume |
|--------------------------| |---------------------------|
| Pod: mysql | | |
| | | | |
+--------v-----------------+ tcp/ip +---------------------------+
| Disk: /dev/drbd0 -->-->--|--->--->--->---| Disk: /dev/drbd0 |
+--------------------------+ +---------------------------+
DRBD Primary DRBD Secondary
- Pod mysql got killed and migrated to k8s-node-2
k8s-node-1 k8s-node-2
+--------------------------+ +---------------------------+
| Kubelet: drbd flexvolume | | Kubelete: drbd flexvolume |
|--------------------------| |---------------------------|
| | | Pod: mysql |
| | | | |
+--------------------------+ tcp/ip +--------v------------------+
| Disk: /dev/drbd0 --<--<--|---<---<---<---| Disk: /dev/drbd0 |
+--------------------------+ +---------------------------+
DRBD Secondary DRBD Primary
- Simple
- No extra storage cluster
- Data natively redundancy and high performance
- Easy to use (StorageClass, PersistentVolume, PersistentVolumeClaim)
- DRBD>=9.0 can be up to 16 nodes, but only at most one primary node simultaneously
- Pod must run as single replica instance (ReadWritOnce)
- PV is available only on resource placed nodes
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