Re: I have 100 servers which need a new backup server added to a text file, and then the backup agent restarted.
- From: "cmdrrickhunter@xxxxxxxx" <conrad.ammon@xxxxxxxxx>
- Date: 3 Jul 2006 01:37:35 -0700
Hehe, yeah, it does feel like swearing =)
That solution works, as long as the network behaves PERFECTLY and
you've allready configured the server to use your SSH key instead of a
password. Expect, by its nature, waits until the right time to say
things
Sample pexpect code:
------------- Code -------------
# assumes hosts is a list of hostnames
for host in hosts:
child = pexpect.spawn("ssh root@%s" % host)
child.expect ('Password:')
child.sendline ("the correct root password")
child.expect ('#') # root prompt
child.sendline("echo 'the new line' >> /etc/config.file")
child.expect('#')
child.sendline("/etc/init.d/myservice restart")
child.expect("#")
child.sendline("logout")
-----------------------------
Or if you prefer a stronger split between data and code you can use
this code. If you need even more functionality than that (such as
pausing for a few seconds after a command), you can start using
callable objects instead of tuples of text.
------------- Code ---------------
# commands is a list of (text-to-wait-for, response-to-send) pairs
commands = [ \
("Password:", "the correct root password"), \
("#", "echo 'the new line' >> /etc/config.file"), \
("#", "/etc/init.d/myservice restart"), \
("#", "logout") ]
for host in hosts:
child = pexpect.spawn("ssh root@%s" % host)
for cmd in commands:
child.expect(cmd[0])
child.sendline(cmd[1])
-------------------------------------------------
You can also tell pexpect to have a timeout on any expect() call.
Shell has its uses. My personal experiance is shell's use is when you
dont expect the client to have a more powerful language installed, or
when a scripts duties are very limited. If ANYTHING involves a space,
dont bother with shells, handling spaces will take more debugging than
the actual code. For example, your quickly written code wouldn't work
because you have " inside ", when you needed single quotes. And if any
of the commands issued have difficult parameters, properly escaping
shell strings is an utter nightmare. A shell solution may work here,
but if the task gets any more complicated, then a new language is
needed.
I'm a toolkit programmer - I keep as many language as I can in my
toolkit. Pexpect was 100% designed for this specific task, so why not
use it. If I was parsing a text file, 9 times out of 10 I'll pull up
PERL, its ment for it.
Ove Pettersen wrote:
I wouldn't use python at all (like swearing on this list???) .... simple
shell-command is more than sufficient.
for server in "server1 server2 server3 .... server100"
do
ssh root@$server "(echo "new line" >> config.file; stop-command ;
sleep 5 ; start-command)"
done
I would however have extended the procedure with a few more checks...
Like:
* only add new line to config-file if it isn't present
* only do restart if config-file was modified
Regards,
.
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