RDMA device plugin for Kubernetes

Introduction

k8s-rdma-device-plugin is a device plugin for Kubernetes to manage RDMA device.

RDMA(remote direct memory access) is a high performance network protocol, which has the following major advantages:

• Zero-copy

  Applications can perform data transfer without the network software stack involvement and data is being send received directly to the buffers without being copied between the network layers.

• Kernel bypass

  Applications can perform data transfer directly from userspace without the need to perform context switches.

• No CPU involvement

  Applications can access remote memory without consuming any CPU in the remote machine. The remote memory machine will be read without any intervention of remote process (or processor). The caches in the remote CPU(s) won't be filled with the accessed memory content.

You can read this post to get more information about RDMA.

This plugin allow you to use RDMA device in container of Kubernetes cluster. And more, We can use this plugin work with sriov-cni to provide high perfmance network connection for distributed application, especially GPU distributed application, such as Tensorflow,Spark, etc.

Quick Start

Build

Install libibverbs package, for CentOS:

# yum install libibverbs-devel -y

Then run build:

# ./build 
# ls bin
k8s-rdma-device-plugin

Work with Kubernetes

• Preparing RDMA node

Install ibverbs libraries, then start kubelet with --feature-gates=DevicePlugins=true.

• Run device plugin daemon process

# bin/k8s-rdma-device-plugin -master eth1 -v 4
INFO[0000] Fetching devices.                            
DEBU[0000] RDMA device list: [{{mlx4_1 uverbs1 /sys/class/infiniband_verbs/uverbs1 /sys/class/infiniband/mlx4_1} eth2} {{mlx4_3 uverbs3 /sys/class/infiniband_verbs/uverbs3 /sys/class/infiniband/mlx4_3} eth4} {{mlx4_2 uverbs2 /sys/class/infiniband_verbs/uverbs2 /sys/class/infiniband/mlx4_2} eth3} {{mlx4_4 uverbs4 /sys/class/infiniband_verbs/uverbs4 /sys/class/infiniband/mlx4_4} eth5}] 
INFO[0000] Starting FS watcher.                         
INFO[0000] Starting OS watcher.                         
INFO[0000] Starting to serve on /var/lib/kubelet/device-plugins/rdma.sock 
INFO[0000] Registered device plugin with Kubelet
...

or deploy it as a daemonset:

# kubectl -n kube-system apply -f rdma-device-plugin.yml
# kubectl -n kube-system get pods
rdma-device-plugin-daemonset-2wbdv         1/1       Running   0          14m
rdma-device-plugin-daemonset-7pwf7         1/1       Running   0          14m

• Run RDMA container

apiVersion: v1
kind: Pod
metadata:
  name: rdma-pod
spec:
  containers:
    - name: rdma-container
      image: mellanox/mofed421_docker:noop
      securityContext:
        capabilities:
          add: ["ALL"]
      resources:
        limits:
          tencent.com/rdma: 1 # requesting 1 RDMA device

Dockerfile for mellanox/mofed421_docker:noop:

FROM mellanox/mofed421_docker:latest

CMD ["/bin/sleep", "360000"]

TODO

Share RDMA device for the containers in the same pod

Generally speaking, for RoCE with k8s, all containers in the same pod should share the same RDMA devices, this is unsupported by k8s now.

Work with sriov-cni plugin

Kubernetes call DP(device plugin) when Admit pod, and call CNI plugin when creating sandbox container. We need a way that pass RDMA device information from DP to CNI. Refer to the issue 32.

Work with NVIDIA GPU plugin

For high performance, we should coordinate the k8s-rdma-device-plugin and nvidia device plugin, and try to make RDMA devices and GPU devices allocated for the same container are located under the same PCIe switch.