Systems Administration

Fabric

Fabric is a library for simplifying system administration tasks. While Chef and Puppet tend to focus on managing servers and system libraries, Fabric is more focused on application level tasks such as deployment.

Install Fabric:

$ pip install fabric

The following code will create two tasks that we can use: memory_usage and deploy. The former will output the memory usage on each machine. The latter will ssh into each server, cd to our project directory, activate the virtual environment, pull the newest codebase, and restart the application server.

from fabric.api import cd, env, prefix, run, task

env.hosts = ['my_server1', 'my_server2']

@task
def memory_usage():
    run('free -m')

@task
def deploy():
    with cd('/var/www/project-env/project'):
        with prefix('. ../bin/activate'):
            run('git pull')
            run('touch app.wsgi')

With the previous code saved in a file named fabfile.py, we can check memory usage with:

$ fab memory_usage
[my_server1] Executing task 'memory'
[my_server1] run: free -m
[my_server1] out:              total     used     free   shared  buffers   cached
[my_server1] out: Mem:          6964     1897     5067        0      166      222
[my_server1] out: -/+ buffers/cache:     1509     5455
[my_server1] out: Swap:            0        0        0

[my_server2] Executing task 'memory'
[my_server2] run: free -m
[my_server2] out:              total     used     free   shared  buffers   cached
[my_server2] out: Mem:          1666      902      764        0      180      572
[my_server2] out: -/+ buffers/cache:      148     1517
[my_server2] out: Swap:          895        1      894

and we can deploy with:

$ fab deploy

Additional features include parallel execution, interaction with remote programs, and host grouping.

Salt

Salt is an open source infrastructure management tool. It supports remote command execution from a central point (master host) to multiple hosts (minions). It also supports system states which can be used to configure multiple servers using simple template files.

Salt supports Python versions 2.6 and 2.7 and can be installed via pip:

$ pip install salt

After configuring a master server and any number of minion hosts, we can run arbitrary shell commands or use pre-built modules of complex commands on our minions.

The following command lists all available minion hosts, using the ping module.

$ salt '*' test.ping

The host filtering is accomplished by matching the minion id, or using the grains system. The grains system uses static host information like the operating system version or the CPU architecture to provide a host taxonomy for the Salt modules.

The following command lists all available minions running CentOS using the grains system:

$ salt -G 'os:CentOS' test.ping

Salt also provides a state system. States can be used to configure the minion hosts.

For example, when a minion host is ordered to read the following state file, it will install and start the Apache server:

apache:
  pkg:
    - installed
  service:
    - running
    - enable: True
    - require:
      - pkg: apache

State files can be written using YAML, the Jinja2 template system or pure Python.

Psutil

Psutil is an interface to different system information (e.g. CPU, memory, disks, network, users and processes).

Here is an example to be aware of some server overload. In case of some failed test (net, CPU) it send an email.

# Functions to get system values:
from psutil import cpu_percent, net_io_counters
# Functions to take a break:
from time import sleep
# Package for email services:
import smtplib
import string
MAX_NET_USAGE = 400000
MAX_ATTACKS = 4
attack = 0
counter = 0
while attack <= MAX_ATTACKS:
    sleep(4)
    counter = counter + 1
    # Check the cpu usage
    if cpu_percent(interval = 1) > 70:
        attack = attack + 1
    # Check the net usage
    neti1 = net_io_counters()[1]
    neto1 = net_io_counters()[0]
    sleep(1)
    neti2 = net_io_counters()[1]
    neto2 = net_io_counters()[0]
    # Calculate the bytes per second
    net = ((neti2+neto2) - (neti1+neto1))/2
    if net > MAX_NET_USAGE:
        attack = attack + 1
    if counter > 25:
        attack = 0
        counter = 0
# Write a very important email if attack is higher then 4
TO = "you@your_email.com"
FROM = "webmaster@your_domain.com"
SUBJECT = "Your domain is out of system resources!"
text = "Go and fix your server!"
BODY = string.join(("From: %s" %FROM,"To: %s" %TO,"Subject: %s" %SUBJECT, "",text), "\r\n")
server = smtplib.SMTP('127.0.0.1')
server.sendmail(FROM, [TO], BODY)
server.quit()

A full terminal application like a widely extended top which is based on psutil and with the ability of a client-server monitoring is glance.

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