updated documentation

Author: Claudio Fahey

README.md

@@ -0,0 +1,94 @@
+
+===================================
+DevOps Scripts
+===================================
+
+[email protected]
+
+This repository contains various Python scripts that can be used to automate various devops tasks.
+
+- configue-ssh.py: configure password-less SSH to remote hosts
+
+- mount-nfs.py: permanently mount an NFS export
+
+- prepare-data-disks.py: partition, format, and mount each of the specified disks.
+
+See the help in each script for usage and examples.
+
+
+Simple Command Execution on Multiple Hosts using Xargs
+------------------------------------------------------
+
+There are many tools for executing commands on multiple hosts. However most such tools require
+additional packages to be installed. For quick and dirty tasks, xargs can easily be used and shown below.
+
+Setup is extremely easily. Create a text file where each line is the FQDN (fully qualified domain name),
+hostname without domain, or the IP address
+of each host in your cluster. If you have different groups of nodes, then you may want to create
+a different file for each group. For instance, the file master.txt may contain the following:
+
+.. parsed-literal::
+
+  mycluster1-master-1.example.com
+  mycluster1-master-2.example.com
+  mycluster1-master-3.example.com
+
+You would then create another file named worker.txt with the FQDN of your worker hosts.
+Now you are ready to automate some tasks as shown in the below examples.
+
+First a quick test. We'll just print the name of each FQDN prefixed with "Hello".
+The **-n 1** option tells xargs to run the supplied command on each line instead of grouping
+them into batches. The **-i** option tells xargs to replace the string **{}** with the
+contents of the line which is our FQDN.
+
+.. parsed-literal::
+
+  $ cat master.txt worker.txt | xargs -n 1 -i echo Hello {}.
+  Hello mycluster1-master-1.example.com.
+  Hello mycluster1-master-2.example.com.
+  Hello mycluster1-master-3.example.com.
+  Hello mycluster1-worker-1.example.com.
+  ...
+
+To run a command on each host using SSH, use this command.
+Note that you'll need password-less SSH configured or you will be prompted for a password on each connection.
+If you haven't configured password-less SSH, see the script configure-ssh.py in this repository.
+
+.. parsed-literal::
+
+  $ cat master.txt worker.txt | xargs -n 1 -i ssh root@{} free -m
+
+To run a compound command on each host:
+
+.. parsed-literal::
+
+  $ cat master.txt worker.txt | xargs -n 1 -i ssh root@{} "hostname ; swapon -s ; free -m"
+
+You can easily filter the list of hosts to run commands on. This is useful for testing on one host before
+running on all hosts.
+
+.. parsed-literal::
+
+  $ cat worker.txt | head -1 | xargs -n 1 -i ssh root@{} free -m
+
+By default, xargs will run the commands sequentially, one host at a time.
+If any command returns an error, xargs will stop and will not run additional commands.
+You can run all commands concurrently with the **-P 0** option. This will also effectively
+ignore any errors.
+
+.. parsed-literal::
+
+  $ cat worker.txt | head -1 | xargs -n 1 -i ssh root@{} yum install -y big_package
+
+You can also use SCP to copy files between the local host and the remote hosts.
+
+.. parsed-literal::
+
+  $ cat master.txt worker.txt | xargs -n 1 -i scp /etc/hosts root@{}:/etc/hosts
+
+Sometimes, you will need to execute sudo on the remote host. When sudo executes on certain
+versions of CentOS or RedHat, it requires a TTY. This can be faked with the ssh **-tt** option.
+
+.. parsed-literal::
+
+  $ cat master.txt worker.txt | xargs -n 1 -i ssh -tt centos@{} sudo mount -a

README.rst

@@ -13,6 +13,9 @@
   %prog -u root host1 host2
     Same as above but it will repeat for host1 and host2.
 
+  %prog -u root $(cat master.txt worker.txt)
+    Same as above but it will repeat for each host listed in the files master.txt and worker.txt.
+
   %prog -u root -p mysecretpassword host1 host2
     To avoid being prompted for a password, specify it with the -p option.
     You must have sshpass installed for this to work.