Horovod in Docker

https://horovod.readthedocs.io/en/stable/docker.html

Step1 构建镜像

GPU

$ mkdir horovod-docker-gpu
$ wget -O horovod-docker-gpu/Dockerfile https://raw.githubusercontent.com/horovod/horovod/master/Dockerfile.gpu
$ docker build -t horovod:latest horovod-docker-gpu

CPU

$ mkdir horovod-docker-gpu
$ wget -O horovod-docker-gpu/Dockerfile https://raw.githubusercontent.com/horovod/horovod/master/Dockerfile.cpu
$ docker build -t horovod:latest horovod-docker-cpu

在单机上运行

GPU 的机器，可以使用 nvidia-docker.

$ nvidia-docker run -it horovod:latest
root@c278c88dd552:/examples# horovodrun -np 4 -H localhost:4 python keras_mnist_advanced.py

在多机上运行

(一)多机运行的条件：ssh免密登陆

http://www.linuxproblem.org/art_9.html

1. First log in on A as user a and generate a pair of authentication keys. Do not enter a passphrase:

a@A:~> ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/a/.ssh/id_rsa): 
Created directory '/home/a/.ssh'.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/a/.ssh/id_rsa.
Your public key has been saved in /home/a/.ssh/id_rsa.pub.
The key fingerprint is:
3e:4f:05:79:3a:9f:96:7c:3b:ad:e9:58:37:bc:37:e4 a@A

2. Now use ssh to create a directory ~/.ssh as user b on B. (The directory may already exist, which is fine):

a@A:~> ssh b@B mkdir -p .ssh
b@B's password: 

3. Finally append a's new public key to b@B:.ssh/authorized_keys and enter b's password one last time:

a@A:~> cat .ssh/id_rsa.pub | ssh b@B 'cat >> .ssh/authorized_keys'
b@B's password: 

4. From now on you can log into B as b from A as a without password:

a@A:~> ssh b@B

（二）主worker

host1$ nvidia-docker run -it --network=host -v /mnt/share/ssh:/root/.ssh horovod:latest
root@c278c88dd552:/examples# horovodrun -np 16 -H host1:4,host2:4,host3:4,host4:4 -p 12345 python keras_mnist_advanced.py

（三）从 workers:

host2$ nvidia-docker run -it --network=host -v /mnt/share/ssh:/root/.ssh horovod:latest 
    bash -c "/usr/sbin/sshd -p 12345; sleep infinity"

host3$ nvidia-docker run -it --network=host -v /mnt/share/ssh:/root/.ssh horovod:latest 
    bash -c "/usr/sbin/sshd -p 12345; sleep infinity"

host4$ nvidia-docker run -it --network=host -v /mnt/share/ssh:/root/.ssh horovod:latest 
    bash -c "/usr/sbin/sshd -p 12345; sleep infinity"

支持远程直接数据存储

$ nvidia-docker run -it --network=host -v /mnt/share/ssh:/root/.ssh --cap-add=IPC_LOCK --device=/dev/infiniband horovod:latest
root@c278c88dd552:/examples# ...