Install , Configure and Use Clush

Clush is an open source tool that allows you to execute commands in parallel across the nodes in the cluster. This blog describes how to install clush, configure and use clush to run commands on multiple nodes in parallel.

The clush utility need to be only installed on one node, usually the primary node (10.10.72.200) in the cluster where we will run commands in parallel and gather stats .


Step 1: Install clustershell package
[root@VM200 ~]# yum --enablerepo=epel install clustershell

To get all cluster nodes and services on mapr cluster.

[root@VM200 ~]# maprcli node list -columns svc
service                                                                       hostname  ip
fileserver,historyserver,webserver,nodemanager,hoststats                      VM200     10.10.72.200
fileserver,hivemeta,webserver,nodemanager,hs2,hoststats                       VM201     10.10.72.201
nodemanager,spark-historyserver,cldb,fileserver,hoststats,hue                 VM202     10.10.72.202
tasktracker,nodemanager,cldb,fileserver,resourcemanager,hoststats,jobtracker  VM203     10.10.72.203


Step 2: Create a "groups" file under "/etc/clustershell/" and add all cluster nodes.
[root@VM200 ~]# vi /etc/clustershell/groups
all:10.10.72.200,10.10.72.201,10.10.72.202,10.10.72.203
[root@VM200 ~]#



[root@VM204 ~]# clush -a date
10.10.72.200: Host key verification failed.
clush: 10.10.72.200: exited with exit code 255
10.10.72.201: Host key verification failed.
clush: 10.10.72.201: exited with exit code 255
10.10.72.202: Host key verification failed.
clush: 10.10.72.202: exited with exit code 255
10.10.72.203: Host key verification failed.
clush: 10.10.72.203: exited with exit code 255

To avoid this "Host key verification failed." message , follow below host key verification steps.
########## Gnerate the key dont give any password on prompt

# ssh-keygen 


Example:

[root@VM204 ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
4a:a0:74:96:51:e2:fa:4f:9d:4d:80:20:1a:96:11:5a root@VM204.mapr.com
The key's randomart image is:
+--[ RSA 2048]----+
....
...


-----------------------------------------------------------------
#### Copy the key to all the nodes for activating password less ssh

# ssh-copy-id 10.10.72.200
# ssh-copy-id 10.10.72.201
# ssh-copy-id 10.10.72.202
# ssh-copy-id 10.10.72.203
# ssh-copy-id 10.10.72.204

Example:

[root@VM200 ~]# ssh-copy-id 10.10.72.200
The authenticity of host '10.10.72.200 (10.10.72.200)' can't be established.
RSA key fingerprint is 20:d4:f6:6e:d5:4b:af:80:bc:21:2b:f6:21:51:19:65.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '10.10.72.200' (RSA) to the list of known hosts.
root@10.10.72.200's password:
Now try logging into the machine, with "ssh '10.10.72.200'", and check in:

  .ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

[root@VM200 ~]# ssh-copy-id 10.10.72.201
[root@VM200 ~]# ssh-copy-id 10.10.72.202
[root@VM200 ~]# ssh-copy-id 10.10.72.203



[root@VM200 ~]# clush -a date
10.10.72.200: Wed Jun  7 17:16:58 IST 2017
10.10.72.201: Wed Jun  7 17:16:43 IST 2017
10.10.72.203: Wed Jun  7 17:18:07 IST 2017
10.10.72.202: Wed Jun  7 17:16:59 IST 2017
[root@VM200 ~]#