access nested node attributes in a chef recipe

If you use chef bookmark this page as you will need to access nested keys at some point.Chef uses ohai to build a hash of each host chef-client is installed on.In a recipe this is stored in a hash named node.If you want to access a value for a key its simple.

ip = node['ipaddress']

Also if you want to determine if a key exists before you try and access it you can use attribute?()

node.attribute?('ipaddress')

BTW in most cases you will want to make sure the key exists because if it doesn’t chef-client will throw an error.

For nested keys its a bit more difficult, first of all you should always make sure the keys exists. This involves using the has_key? method in nested if statements.Then you can just pull the value from the keys.Below is one way to do it in a recipe.In this example I am making sure the keys filesystem>/dev/sda6>mount exist in the node hash.Then once I’m sure the hash exists I pull out the value.

if node.has_key? "filesystem"     if node["filesystem"].has_key? "/dev/sda6"        if node["filesystem"]["/dev/sda6"].has_key? "mount"           if node['filesystem']['/dev/sda6']['mount'] == '/srv'                execute "foo" do                command "touch /tmp/nested_keys_exist!"                action :run              end           end       end     end  end
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riak cluster backup script with compression #riak

This script will create a compressed back up of a riak cluster and keep the previous days copy.I still have to add restoring as an option.

#!/usr/bin/env ruby  t = Time.new  f = t -86400  today = t.strftime("%Y-%m-%d")  yesterday = f.strftime("%Y-%m-%d")  def delete_old()    unless Dir.glob('/net/fs11/srv/posterous/nfs/riak/*-old').empty?      l = Dir.glob('/net/fs11/srv/posterous/nfs/riak/*-old')      puts "deleting oldeest backup"      File.delete(l[0])    end  end  def rotate_last(yesterday)    f = "/net/fs11/srv/posterous/nfs/riak/riak_backup-" + yesterday.chomp  + ".bz2"    t = f + "-old"    if  File.exists?(f)      puts "rotating old backup to old"      File.rename(f,t)    end  end  def run_backup(today)    puts "creating backup file"    dump = "/usr/sbin/riak-admin backup riak@172.27.0.113 riak       /net/fs11/srv/posterous/nfs/riak/riak_backup-" + today.chomp + " all"    `#{dump}`  end  def compress(today)    puts "compressing backup"    compress = "/usr/bin/pbzip2 /net/fs11/srv/posterous/nfs/riak/riak_backup-" + today.chomp    `#{compress}`  end  delete_old()  rotate_last(yesterday)  run_backup(today)  compress(today)