Manage Nodes with Chef Client - Learning Chef - page 122

NOTE
The string variant node['virtualization']['system'] tends to be the most commonly
used node attribute form. However, because attribute expressions are evaluated as a Mash ,
you'll encounter Chef code that uses the other possible Mash variants:
▪ node[:virtualization][:system]
▪ node['virtualization']['system']
▪ node.virtualization.system
Use a form that makes the most sense to you.
Let's make these examples more concrete by using them in a Chef recipe.
Accessing Node Information
As we discussed in the last section, chef-client collects a lot of information about the state
of a node using ohai . Collecting this information is necessary so that Chef can intelligently
reason how to put the node into the desired configuration specified in a recipe. Chef does not
keep this information to itself. It makes this information available to your Chef code as a
node attribute. An attribute is a variable maintained by Chef.
Let's use the log resource that you just used in Your First Chef-Client Run to print out some
node information. Create a new file called info.rb on the node with the following sequence of
commands:
[vagrant@default-centos65 ~]$ cat << EOF > info.rb
> log "IP Address: #{node['ipaddress']}"
> log "MAC Address: #{node['macaddress']}"
> log "OS Platform: #{node['platform']} #{node['platform_version']}"
> log "Running on a #{node['virtualization']['system']} \
> #{node['virtualization']['role']}"
> log "Hostname: #{node['hostname']}"
> EOF
This command will produce the source file seen in Example 6-3 .