This is a text-only version of the following page on https://raymii.org:
---
Title : Chef: search in recipe based on roles or recipes
Author : Remy van Elst
Date : 08-10-2013
URL : https://raymii.org/s/tutorials/Chef_search_in_recipe_on_roles_or_recipes.html
Format : Markdown/HTML
---
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][2]. 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
end
service "collectd" do
supports :start =>true, :restart => true, :stop => true
action [:enable, :start]
end
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]"
variables(
:graphite_servers => graphite_servers
)
end
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| -%>
<Carbon>
Host "<%= graphite_server['ipaddress'] -%>"
Port "2003"
EscapeCharacter "_"
SeparateInstances true
StoreRates false
AlwaysAppendDS false
</Carbon>
<% end -%>
</Plugin>
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.
[1]: https://www.digitalocean.com/?refcode=7435ae6b8212
[2]: https://github.com/hw-cookbooks/graphite
---
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