Rudder techniques

file_from_template_mustache

Build a file from a mustache template.

⚙️ Compatible targets: Linux, Windows

Parameters

Outcome conditions

You need to replace ${path} with its actual canonified value.

• ✅ Ok: file_from_template_${path}_ok
  • ☑️ Already compliant: file_from_template_${path}_kept
  • 🟨 Repaired: file_from_template_${path}_repaired
• ❌ Error: file_from_template_${path}_error

Example

method: file_from_template_mustache
params:
  path: VALUE
  source_template: VALUE

Documentation

See file_from_template_type for general documentation about templates usage.

Syntax

Mustache is a logic-less templating language, available in a lot of languages, and used for file templating in Rudder. The mustache syntax reference is https://mustache.github.io/mustache.5.html. The Windows implementation follows the standard, the Unix one is a bit richer as describe below.

We will here describe the way to get agent data into a template. Ass explained in the general templating documentation, we can access various data in a mustache template.

The main specificity compared to standard mustache syntax of prefixes in all expanded values:

• classes to access conditions
• vars to access all variables

Classes

Here is how to display content depending on conditions definition:

{{#classes.my_condition}}
   content when my_condition is defined
{{/classes.my_condition}}

{{^classes.my_condition}}
   content when my_condition is *not* defined
{{/classes.my_condition}}

Note: You cannot use condition expressions here.

Scalar variable

Here is how to display a scalar variable value (integer, string, ...), if you have defined variable_string("variable_prefix", "my_variable", "my_value"):

{{{vars.variable_prefix.my_variable}}}

We use the triple {{{ }}} to avoid escaping html entities.

Iteration

Iteration is done using a syntax similar to scalar variables, but applied on container variables.

• Use {{#vars.container}} content {{/vars.container}} to iterate
• Use {{{.}}} for the current element value in iteration
• Use {{{key}}} for the key value in current element
• Use {{{.key}}} for the key value in current element (Linux only)
• Use {{{@}}} for the current element key in iteration (Linux only)

To iterate over a list, for example defined with:

variable_iterator("variable_prefix", "iterator_name", "a,b,c", ",")

Use the following file:

{{#vars.variable_prefix.iterator_name}}
{{{.}}} is the current iterator_name value
{{/vars.variable_prefix.iterator_name}}

Which will be expanded as:

a is the current iterator_name value
b is the current iterator_name value
c is the current iterator_name value

To iterate over a container defined by the following json file, loaded with variable_dict_from_file("variable_prefix", "dict_name", "path"):

{
   "hosts": [
       "host1",
       "host2"
   ],
   "files": [
       {"name": "file1", "path": "/path1", "users": [ "user1", "user11" ] },
       {"name": "file2", "path": "/path2", "users": [ "user2" ] }
   ],
   "properties": {
       "prop1": "value1",
       "prop2": "value2"
   }
}

Use the following template:

{{#vars.variable_prefix.dict_name.hosts}}
{{{.}}} is the current hosts value
{{/vars.variable_prefix.dict_name.hosts}}

# will display the name and path of the current file
{{#vars.variable_prefix.dict_name.files}}
{{{name}}}: {{{path}}}
{{/vars.variable_prefix.dict_name.files}}
# Lines below will only be properly rendered in unix Nodes
# will display the users list of each file
{{#vars.variable_prefix.dict_name.files}}
{{{name}}}:{{#users}} {{{.}}}{{/users}}
{{/vars.variable_prefix.dict_name.files}}


# will display the current properties key/value pair
{{#vars.variable_prefix.dict_name.properties}}
{{{@}}} -> {{{.}}}
{{/vars.variable_prefix.dict_name.properties}}

Which will be expanded as:

host1 is the current hosts value
host2 is the current hosts value

# will display the name and path of the current file
file1: /path1
file2: /path2

# Lines below will only be properly rendered in unix Nodes
# will display the users list of each file
file1: user1 user11
file2: user2

# will display the current properties key/value pair
prop1 -> value1
prop2 -> value2

Note: You can use {{#-top-}} ... {{/-top-}} to iterate over the top level container.

System variables

Some sys dict variables (like sys.ipv4) are also accessible as string, for example:

• ${sys.ipv4} gives 54.32.12.4
• $[sys.ipv4[ethO]} gives 54.32.12.4
• $[sys.ipv4[eth1]} gives 10.45.3.2

These variables are not accessible as dict in the templating data, but are represented as string:

• ipv4 is a string variable in the sys dict with value 54.32.12.4
• ipv4[ethO] is a string variable in the sys dict with value 54.32.12.4
• ipv4 is not accessible as a dict in the template

To access these value, use the following syntax in your mustache templates:

{{{vars.sys.ipv4[eth0]}}}