Manage only a section of a config file with Puppet (multiline file_line)

Question

There is a config file e.g. /etc/network/interfaces. I want to manage only a certain section of that file using Puppet.

Example:

# At the beginning at least is some dynamic content that can be different
# from machine to machine and changed by an admin manually
auto eth0
iface eth0 inet static
    address 192.168.108.5
    netmask 255.255.255.0

# BEGIN PUPPET WLAN0
allow-hotplug wlan0
iface wlan0 inet static
    address 192.168.109.5
    netmask 255.255.255.0
# END PUPPET WLAN0

# Potentially more stuff that I do not want to touch through Puppet
# But could be static if it makes it more easy. E.g. simply force sections to end of file.

The stdlib file_line resource is very close to what I need. A regex and content to replace a match with. However, unfortunately, there is no way to make file_line match over multiple lines and replace with new content.

Alternative 1: create a bash script: ugly Exec resources and temp files.

Alternaitve 2: Use Augeas: seems overkill for a simple search & replace.

Is there another module than stdlib that allows me to do a regex match & replace over multiple lines?

Any other handcraft solutions better than juggling temp bash script and Exec resource?

Answer 1

You can simply use a single line match as the placeholder for a multi-line value:

$wlan_address = [...]
$wlan_netmask = [...]
$wlan_string = "allow-hotplug wlan0
iface wlan0 inet static
    address ${wlan_address}
    netmask ${wlan_netmask}"

file_line { 'wlan0':
  path  => '/etc/network/interfaces',
  line  => $wlan_string,
  match => '^# PUPPET WLAN0$',
}

Answer 2

Managing part of a file is a configuration management anti pattern that should be discouraged as much as possible.

You have already identified the various tools that can do this.

• Augeas
• stdlib/file_line
• exec + sed

You can alternatively manage the whole file, and do an 'onlyif' so the file isn't overwritten every time.

As you have found, file_line only really works on init style config files, that are single line.

Your best bet will be to do an exec on that file with a sed insert.

Answer 3

There is a module in puppet already installed by default called:puppetlabs-stdlib and within this module a defined type called file_line which does the trick :) Here is my case scenario under the /manifests/node.pp:

node elk.ershandc.org {
...
file_line { 'backup_authorized_key' :
    ensure => 'present',
    path   => '/root/.ssh/authorized_keys',
    line   =>'ssh-rsaAAAAB3NzaC1yc2EAAAADAQABAAABAQC1ZCi/K0hlffi9ZUmveJ05l301RE6u/TzrCK+i54edzN5stR/tTjd28vFIup10HTYoZxbqBgRMrxVGDnfwtaSsCZH31g2/flZBxSZGzjySKeUqnf/YyGJP6my/IjA4xcKVcPDPx2FF/u1Sd07y7wnLizjAhtIOwq1daiCcRbXkIxfpobQt/RtJLAyDA1CwACr9NWmAezS0rnaYXRBQrmrkCBx91fMhKsarvxB3z4mTG8wVNwXvE9g2Hps6bRzff0hIXaIoVFYHwqmyIkN+4xCDGcjt3TjZp0zvTK20RR7DNOHxOGs8GBhcvitEkGY/JXgA4AJ26ncfXaspaUgEM/Rt root@devop-testbed'
 }

...
}

Answer 4

If you can guarantee the other file contents are static, you can just make that file into a template and keep the static sections unchanged. Example:

auto eth0
iface eth0 inet static
address 192.168.108.5
netmask 255.255.255.0

# BEGIN PUPPET WLAN0
allow-hotplug wlan0
iface wlan0 inet static
    address <%= wlan0_address %>
    netmask <%= wlan0_netmask %>
# END PUPPET WLAN0

# More stuff that I do not want to touch through Puppet
# Static content here

This example assumes that you have defined the variables $wlan0_address and $wlan0_netmask elsewhere.

You then deploy with a file resource:

file{'interfaces':
        ensure  => file,
        path    => '/etc/network/interfaces',
        content => template('/path/to/template'),
}