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Chef: search in recipe based on roles or recipes

Published: 08-10-2013 | Author: Remy van Elst | Text only version of this article

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Chef supports a very powerfull search syntax which allows you for example to search all nodes with the graphite-server role and get their IP addresses. This tutorial shows you how to search based on a role a node has or a recipe a node has, plus an example config file with erb syntax. It has an example cookbook which sets up collectd as client and graphite as server. It shows you how to use the search function of Chef to get the IP addresses of the graphite servers and place those in the collectd config files. This technique is applicable to all kinds of services that use a client-server model, for example, munin, haproxy, zabbix and many more.

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Lets say you want to build a graphite server which gets data from a lot of collectd clients. You can hard code it in the collectd.conf file, but this is not preferred, what if your graphite server changes? What if you want to add a graphite server and have all your clients automagically also send data to that server? Here is where the following comes in handy.

You can use this graphite cookbook. If you add the graphite recipe to a node, it will install everything needed for a graphite server, including the web ui. Now, you can also create a role graphite_server and add the recipe to that, then add the role to a node. This way you have a graphite server running.

collectd 5.1 or higher is required for graphite support. My environment currently runs mostly on Ubuntu 12.04 LTS, which has collectd 4 in the repositories. Therefore I build a package myself, but there are also PPA's available. I also run my own repositories, so I can just use the collectd-core package, if you don't have a collectd 5.1 or higher package then the following example won't work for you.

This very simple cookbook installs the collectd package and sets the config file. Take a look at it:

package "collectd-core" do
    action :install

service "collectd" do
  supports :start =>true, :restart => true, :stop => true
  action [:enable, :start]

node.set[:collectd][:client] = true

graphite_servers = search(:node, 'recipes:"graphite"')

template "/etc/collectd/collectd.conf" do
    source "collectd.conf.erb"
    owner "root"
    group "root"
    mode 0644
    notifies :restart, "service[collectd]"
        :graphite_servers => graphite_servers

The following line does the search magic:

graphite_servers = search(:node, 'recipes:"graphite"')

It searches the Chef server for all nodes with the graphite recipe and makes that available in this cookbook. Then it passes it on to the template, which we will discuss below. If you don't want to search on recipes but for example on roles, you can use the following code:

graphite_servers = search(:node, 'role:graphite-server')

or on an attribute set in the node:

graphite_servers = search(:node, 'graphite_server:true')

Now the template (collectd.conf.erb) is a standard collectd template with some erb to enumerate the information in the graphite_servers variable. Skip to the bottom to see it:

# Managed by Chef for node <%= node['fqdn'] -%>.
# Do not edit manually, your changes will be overwritten.
Hostname <%= node['fqdn'] -%>
FQDNLookup false
Interval 30
ReadThreads 1
LoadPlugin syslog
LogLevel info
LoadPlugin cpu
LoadPlugin df
LoadPlugin disk
LoadPlugin entropy
LoadPlugin interface
LoadPlugin irq
LoadPlugin load
LoadPlugin memory
LoadPlugin processes
LoadPlugin rrdtool
LoadPlugin swap
LoadPlugin users
LoadPlugin network
LoadPlugin iptables
LoadPlugin uptime
LoadPlugin "write_graphite"
<Plugin "write_graphite">
<% @graphite_servers.each do |graphite_server| -%>
   Host "<%= graphite_server['ipaddress'] -%>"
   Port "2003"
   EscapeCharacter "_"
   SeparateInstances true
   StoreRates false
   AlwaysAppendDS false
 <% end -%>

This part starts a loop, which will loop trough all the values in the array it got from the cookbook:

<% @graphite_servers.each do |graphite_server| -%>

Then this part does another lookup to get the node's IP address:

Host "<%= graphite_server['ipaddress'] -%>"

You can change that to get any other attribute from a node, in this example we need the IP address.

This last part ends the loop:

 <% end -%>

This will result in a config file with all the graphite servers you have in your Chef environment. One of the big plus points is that you can add or remove graphite servers whenever you want without the nodes having issues. Need to scale up a few servers? Just deploy some new nodes and all the clients will use them. Scaling down? No issue, all the clients will stop using them without manual action.

This technique is very applicable to other client-server models, like Munin. Or, any other setup like this.

Tags: chef , collectd , cookbooks , deployment , devops , graphite , roles , ruby , tutorials