puppet Hiera

 先看automatical parameter lookup，
init.pp

1. class auto (
   
2. $servers,
   
3. $autook,
   
4. ){
   
5. 
   
6. file {'/tmp/foo':
   
7.    content =>template("auto/foo.erb"),
   
8. }
   
9. }

foo.erb

1. some config snippet
   
2. <%= @autook %>
   
3. <%# comment -%>
   
4. <%% print a %%>
   
5. <% @servers.each do |s| -%>
   
6. <%= "ntpserver: #{s}" %>
   
7. <%- end -%>

# yaml

1. ---
   
2. auto::autook: "ok"
   
3. auto::servers:
   
4.   - www.example.com
   
5.   - 0.us.pool.ntp.org
   
6.   - 1.us.pool.ntp.org
   
7.   - 2.us.pool.ntp.org

结果：
some config snippet
ok......

ntpserver: www.example.com
ntpserver: 0.us.pool.ntp.org
ntpserver: 1.us.pool.ntp.org
ntpserver: 2.us.pool.ntp.org

1. puppet config print |grep data_binding
   
2. data_binding_terminus = hiera

If you need to disable this feature, then you can set data_binding_terminus = none in your master’s puppet.conf

然后 :merge_behavior 在hiera.yaml里面，默认是native(在key重复的情况下，取第一个出现的）, 还有个deep(不用看，官方不推荐），deeper（需要 sudo puppetserver gem install deep_merge --no-ri --no-rdoc来安装） 而deeper的行为是merge recursively; in the event of a conflict, allow higher priority values to win.
# common.yaml
---
site_users:
  bob:
    uid: 501
    shell: /bin/bash
  ash:
    uid: 502
    shell: /bin/zsh
    group: common
# %{::trusted.certname}

---
site_users:
  jen:
    uid: 503
    shell: /bin/zsh
    group: deglitch
  bob:
    uid: 1000
    group: deglitch

hierarchy里面common在最后，在deeper的行为下：

{
  "bob"=>{
    group=>"deglitch", #取第一次出现的
    uid=>1000,  # 取第一次出现的
    shell=>"/bin/bash"  # merge过来的
  },
  "jen"=>{
    group=>"deglitch",
    uid=>503
    shell=>"/bin/zsh",
  },
  "ash"=>{
    group=>"common",
    uid=>502,
    shell=>"/bin/zsh"
  }
}

还有几个函数，hiera，hiera_array, hiera_hash, 第一个可以查任意的数据类型，string/array/hash，但对于hash/array不做merge, 后2个顾名思义。hiera_include来查询class,有人把其当做ENC来用，但我不推荐。
# site.pp
hiera_include('classes') 然后在yaml写自己的名字。

smtpserver: "mail.%{scope('::domain')}"   # 用%来调用
wordpress::database_server: "%{hiera('instances::mysql::public_hostname')}" 

he literal lookup function allows you to escape ‘%{}’ in Hiera data. This is useful when you have data containing this literal string, as with some Apache variables like %{SERVER_NAME} or %{QUERY_STRING}.