Does your configuration code smell?

Does Your Conﬁguration Code
Smell?
Tushar Sharma

“Smells”
Code Smell
…certain structures in the code
that suggest (sometimes they
scream for) the possibility of
refactoring.

“Smells”
Design Smells
“Design smells are certain
structures in the design that
indicate violation of fundamental
design principles and negatively
impact design quality.”

“Smells”
Configuration Smells

“Infrastructure as Code” (IaC)

Puppet example
package { 'apache2':
require => Exec['apt-update'],
ensure => installed,
}
service { 'apache2':
ensure => running,
}
user { 'tushar':
ensure => present,
uid => '1000',
gid => '1000',
shell => '/bin/bash',
home => '/home/tushar'
}
Configuration management tools:
Ansible, Chef, CFEngine, Puppet

Software System
IaC and Traditional SE
Production code
Infrastructure,
configuration
code, tools and
services
Apply
traditional
software
engineering
practices

Configuration smells
“Configuration smells are the characteristics of a
configuration program or script that violate the
recommended best practices and potentially
affect the program’s quality in a negative way.”

Implementation configuration smells

import 'classes/*'
# TODO: fix deprecated statement
class app-studio (String $version = ‘latest')
{
$primary_config_file = 'config'
$source_config = 'config.source'
if $version == ’44’ or $version == ‘4.2’ or $version != ‘4.5’ or $version ==
‘4.9’{
case $::operatingsystem {
'debian': {
apt::source { 'packages.dotdeb.org-repo.app':
location => 'http://repo.app.com/dotdeb/',
release => $::lsbdistcodename,
repos => 'all',
include_src => true
include_src => true
}
}
Deprecated Statement Usage

import 'classes/*'
{
‘4.9’{
'debian': {
repos => 'all',
include_src => true
include_src => true
}
}
Incomplete Task

import 'classes/*'
{
‘4.9’{
'debian': {
repos => 'all',
include_src => true
include_src => true
}
}
Long Statement
Complex Expression

import 'classes/*'
{
‘4.9’{
'debian': {
repos => 'all',
include_src => true
include_src => true
}
}
Missing Default Case

import 'classes/*'
{
‘4.9’{
'debian': {
repos => 'all',
include_src => true
include_src => true
}
}
Duplicate Entity

elsif $version in ['33', '3.3'] {
}
if $::kernelversion =~ /^(2.2)/ {
$appversion = '3.5'
} elsif $::kernelversion =~ /^(2.1)/ {
exec {"download_app_studio":
command => "wget $url",
timeout => 0,
}
}
$version = '3.4' ? {undef => $primary_config_file, default => $source_config}
file { "/root/.app":
mode => '644',
ensure => present
}
}
Missing Conditional

}
$appversion = '3.5'
timeout => 0,
}
}
mode => '644',
ensure => present
}
}
Improper Quote Usage

}
$appversion = '3.5'
timeout => 0,
}
}
mode => '644',
ensure => present
}
}
Unguarded Variable

}
$appversion = '3.5'
timeout => 0,
}
}
mode => '644',
ensure => present
}
}
Improper Alignment

}
$appversion = '3.5'
timeout => 0,
}
}
mode => '644',
ensure => present
}
}
Invalid Property Value

}
$appversion = '3.5'
timeout => 0,
}
}
mode => '644',
ensure => present
}
}
Misplaced Attribute

class package::web {
…
}
class package::mail {
…
}
class package::environment {
…
}
class package::user {
…
}
package.pp

class apache {
…
}
…
}
service { 'mysql':
…
}
package { 'php5':
…
}
file { ‘/etc/apache2/ports.conf':
…
}
user { ‘mitchell':
…
}
}
apache.pp

Multifaceted Abstraction
•  
Each abstraction should be designed to specify the properties of a
single piece of software.

Unnecessary Abstraction
A class, ‘define’, or module must contain declarations or
statements specifying the properties of a desired system.

class web {
exec { ‘hadoop-yarn’:
…
}
exec { ‘apache-util-set’:
…
}
exec { ‘smail-invoke’:
…
}
exec { ‘postfix-set’:
…
}
}
init.pp

Imperative Abstraction
An abstraction containing numerous imperative
statements suffers from imperative abstraction smell.

…
}
…
}
service { 'mysql':
…
}
package { 'php5':
…
}
…
}
…
}
init.pp

Missing Abstraction
A module suffers from the missing abstraction smell when
resources and language elements are declared and used
without encapsulating them in an abstraction.

class apache {
…
}
…
}
…
}
…
}
web.pp
class apache {
…
}
…
}
…
}
…
}
server.pp

Duplicate Block
A duplicate block of statements more than a threshold
indicates that probably a suitable abstraction definition is
missing.

…
}
…
}
service { 'mysql':
…
}
package { 'php5':
…
}
…
}
…
}
…
}
…
}
service { 'mysql':
…
}
package { 'php5':
…
}
…
}
…
}
…
}
…
}
service { 'mysql':
…
}
package { 'php5':
…
}
…
}
…
}
init.pp

Insufficient Modularisation
An abstraction suffers from this smell when it is large or
complex and thus can be modularized further.

Unstructured Module
Each module in a configuration repository must have a
well-defined and consistent module structure.
RepoName
Manifests
Modules
README
…
Apache
Adobe
…
files
lib
manifests
spec
templates
tests
README
…

Dense Structure
This smell arises when a configuration code repository
has excessive and dense dependencies.

Weekend Modularity
This smell arises when a module exhibits high
coupling and low cohesion.
Modularity ratio (A) =
Cohesion(A)
Coupling(A)

Implications of smells
The straw that broke the camel's back

Detecting configuration smells
• Puppet-lint [1]
• Additional custom rules in Puppeteer
Design configuration smells
• Puppeteer [2] — an open source tool
1. http://puppet-lint.com/
2. https://github.com/tushartushar/Puppeteer

Mining GitHub Repositories
Repositories 4,621
Puppet files 142,662
Class declarations 132,323
Define declarations 39,263
File resources 117,286
Package resources 49,841
Service resources 18,737
Exec declarations 43,468
Lines of code (Puppet only) 8,948,611
http://www.tusharma.in/research/does-your-configuration-code-smell-msr-2016/

Let us summarize
M
E
L
S
U
P
E
E
R
II
P
T
U
I NM Y
I
IA A BN
C

Let us summarize
M
E
L
S
U
P
E
E
R
II
P
T
U
IA NM Y
I
IA A BN
C

Let us summarize
S
M
E
L
S
U
P
E
E
R
L II
P
T
U
IA NM Y
I
IA A BN
C

Let us summarize
S
M
E
L
S
U
P
P
E
E
R
L II
P
T
U
IA NM Y
I
IT A A BN
C

Thank you!!
Courtesy: spikedmath.com
Tushar Sharma
tusharsharma@ieee.org
@Sharma__Tushar

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