Appendix A. Template writing reference

Embedded Ruby (ERB) is a tool for generating text files based on templates that combine plain text with Ruby code. Red Hat Satellite uses ERB syntax in the following cases:

Provisioning templates: For more information, see Creating Provisioning Templates in Provisioning hosts.
Remote execution job templates: For more information, see Chapter 13, Configuring and setting up remote jobs.
Report templates: For more information, see Chapter 11, Using report templates to monitor hosts.
Templates for partition tables: For more information, see Creating Partition Tables in Provisioning hosts.
Smart Class Parameters: For more information, see Configuring Puppet Smart Class Parameters in Managing configurations by using Puppet integration.

This section provides an overview of Satellite-specific macros and variables that can be used in ERB templates along with some usage examples. Note that the default templates provided by Red Hat Satellite (Hosts > Templates > Provisioning Templates, Hosts > Templates > Job templates, Monitor > Reports > Report Templates ) also provide a good source of ERB syntax examples.

When provisioning a host or running a remote job, the code in the ERB is executed and the variables are replaced with the host specific values. This process is referred to as rendering. Satellite Server has the safemode rendering option enabled by default, which prevents any harmful code being executed from templates.

A.1. Accessing the template writing reference in the Satellite web UI

You can access the template writing reference document in the Satellite web UI.

Procedure

Log in to the Satellite web UI.
In the Satellite web UI, navigate to Administer > About.
Click the Templates DSL link in the Support section.

A.2. Using autocompletion in templates

You can access a list of available macros and usage information in the template editor with the autocompletion option. This works for all templates within Satellite.

Procedure

In the Satellite web UI, navigate to either Hosts > Templates > Partition tables, Hosts > Templates > Provisioning Templates, or Hosts > Templates > Job templates.
Click the settings icon at the top right corner of the template editor and select Autocompletion.
Press Ctrl + Space in the template editor to access a list of all available macros. You can narrow down the list of macros by typing in more information about what you are looking for. For example, if you are looking for a method to list the ID of the content source for a host, you can type host and check the list of available macros for content source.
A window next to the dropdown provides a description of the macro, its usage, and the value it will return.
When you find the method you are looking for, hit Enter to input the method.

You can also enable Live Autocompletion in the settings menu to view a list of macros that match the pattern whenever you type something. However, this might input macros in unintended places, like package names in a provisioning template.

A.3. Writing ERB templates

The following tags are the most important and commonly used in ERB templates:

<% %>

All Ruby code is enclosed within <% %> in an ERB template. The code is executed when the template is rendered. It can contain Ruby control flow structures as well as Satellite-specific macros and variables. For example:

<% if @host.operatingsystem.family == "Redhat" && @host.operatingsystem.major.to_i > 6 -%>
systemctl <%= input("action") %> <%= input("service") %>
<% else -%>
service <%= input("service") %> <%= input("action") %>
<% end -%>

Note that this template silently performs an action with a service and returns nothing at the output.

<%= %>

This provides the same functionality as <% %> but when the template is executed, the code output is inserted into the template. This is useful for variable substitution, for example:

Example input:

echo <%= @host.name %>

Example rendering:

host.example.com

Example input:

<% server_name = @host.fqdn %>
<%= server_name %>

Example rendering:

host.example.com

Note that if you enter an incorrect variable, no output is returned. However, if you try to call a method on an incorrect variable, the following error message returns:

Example input:

<%= @example_incorrect_variable.fqdn -%>

Example rendering:

undefined method `fqdn' for nil:NilClass

<% -%>, <%= -%>

By default, a newline character is inserted after a Ruby block if it is closed at the end of a line:

Example input:

<%= "line1" %>
<%= "line2" %>

Example rendering:

line1
line2

To change the default behavior, modify the enclosing mark with -%>:

Example input:

<%= "line1" -%>
<%= "line2" %>

Example rendering:

line1line2

This is used to reduce the number of lines, where Ruby syntax permits, in rendered templates. White spaces in ERB tags are ignored.

An example of how this would be used in a report template to remove unnecessary newlines between a FQDN and IP address:

Example input:

<%= @host.fqdn -%>
<%= @host.ip -%>

Example rendering:

host.example.com10.10.181.216

<%# %>

Encloses a comment that is ignored during template rendering:

Example input:

<%# A comment %>

This generates no output.

Indentation in ERB templates

Because of the varying lengths of the ERB tags, indenting the ERB syntax might seem messy. ERB syntax ignore white space. One method of handling the indentation is to declare the ERB tag at the beginning of each new line and then use white space within the ERB tag to outline the relationships within the syntax, for example:

<%- load_hosts.each do |host| -%>
<%-   if host.build? %>
<%=     host.name %> build is in progress
<%-   end %>
<%- end %>

A.4. Troubleshooting ERB templates

The Satellite web UI provides two ways to verify the template rendering for a specific host:

Directly in the template editor – when editing a template (under Hosts > Templates > Partition tables, Hosts > Templates > Provisioning Templates, or Hosts > Templates > Job templates), on the Template tab click Preview and select a host from the list. The template then renders in the text field using the selected host’s parameters. Preview failures can help to identify issues in your template.
At the host’s details page – select a host at Hosts > All Hosts and click the Templates tab to list templates associated with the host. Select Review from the list next to the selected template to view it’s rendered version.

A.5. Generic Satellite-specific macros

This section lists Satellite-specific macros for ERB templates. You can use the macros listed in the following table across all kinds of templates.

Table A.1. Generic macros
Name	Description
indent(n)	Indents the block of code by n spaces, useful when using a snippet template that is not indented.
foreman_url(kind)	Returns the full URL to host-rendered templates of the given kind. For example, templates of the "provision" type usually reside at `http://HOST/unattended/provision`.
snippet(name)	Renders the specified snippet template. Useful for nesting provisioning templates.
snippets(file)	Renders the specified snippet found in the Foreman database, attempts to load it from the `unattended/snippets/` directory if it is not found in the database.
snippet_if_exists(name)	Renders the specified snippet, skips if no snippet with the specified name is found.

A.6. Template macros

If you want to write custom templates, you can use some of the following macros. Depending on the template type, some of the following macros have different requirements.

For more information about the available macros for report templates, in the Satellite web UI, navigate to Monitor > Reports > Report Templates, and click Create Template. In the Create Template window, click the Help tab.

For more information about the available macros for job templates, in the Satellite web UI, navigate to Hosts > Templates > Job templates, and click the New Job Template. In the New Job Template window, click the Help tab.

input

Using the input macro, you can customize the input data that the template can work with. You can define the input name, type, and the options that are available for users. For report templates, you can only use user inputs. When you define a new input and save the template, you can then reference the input in the ERB syntax of the template body.

<%= input('cpus') %>

This loads the value from user input cpus.

load_hosts

Using the load_hosts macro, you can generate a complete list of hosts.

<%- load_hosts().each_record do |host| -%>
<%=     host.name %>

Use the load_hosts macro with the each_record macro to load records in batches of 1000 to reduce memory consumption.

If you want to filter the list of hosts for the report, you can add the option search: input(‘Example_Host’):

<% load_hosts(search: input('Example_Host')).each_record do |host| -%>
<%=  host.name %>
<% end -%>

In this example, you first create an input that you then use to refine the search criteria that the load_hosts macro retrieves.

report_row

Using the report_row macro, you can create a formatted report for ease of analysis. The report_row macro requires the report_render macro to generate the output.

Example input:

<%- load_hosts(search: input('Example_Host')).each_record do |host| -%>
<%-   report_row(
        'Server FQDN': host.name
      ) -%>
<%- end -%>
<%= report_render -%>

Example rendering:

Server FQDN
host1.example.com
host2.example.com
host3.example.com
host4.example.com
host5.example.com
host6.example.com

You can add extra columns to the report by adding another header. The following example adds IP addresses to the report:

Example input:

<%- load_hosts(search: input('host')).each_record do |host| -%>
<%-   report_row(
      'Server FQDN': host.name,
           'IP': host.ip
      ) -%>
<%- end -%>
<%= report_render -%>

Example rendering:

Server FQDN,IP
host1.example.com,10.8.30.228
host2.example.com,10.8.30.227
host3.example.com,10.8.30.226
host4.example.com,10.8.30.225
host5.example.com,10.8.30.224
host6.example.com,10.8.30.223

report_render

This macro is available only for report templates.

Using the report_render macro, you create the output for the report. During the template rendering process, you can select the format that you want for the report. YAML, JSON, HTML, and CSV formats are supported.

<%= report_render -%>

render_template()

This macro is available only for job templates.

Using this macro, you can render a specific template. You can also enable and define arguments that you want to pass to the template.

truthy

Using the truthy macro, you can declare if the value passed is true or false, regardless of whether the value is an integer or boolean or string.

This macro helps to avoid confusion when your template contains multiple value types. For example, the boolean value true is not the same as the string value "true". With this macro, you can declare how you want the template to interpret the value and avoid confusion.

You can use truthy to declare values as follows:

truthy?("true") => true
truthy?(1) => true
truthy?("false") => false
truthy?(0) => false

falsy

The falsy macro serves the same purpose as the truthy macro.

Using the falsy macro, you can declare if the value passed in is true or false, regardless of whether the value is an integer or boolean or string.

You can use falsy to declare values as follows:

falsy?("true") => false
falsy?(1) => false
falsy?("false") => true
falsy?(0) => true

A.7. Host-specific variables

The following variables enable using host data within templates. Note that job templates accept only @host variables.

Table A.2. Host-specific variables and macros
Name	Description
@host.architecture	The architecture of the host.
@host.bond_interfaces	Returns an array of all bonded interfaces. See Section A.10, “Parsing arrays”.
@host.capabilities	The method of system provisioning, can be either build (for example kickstart) or image.
@host.certname	The SSL certificate name of the host.
@host.diskLayout	The disk layout of the host. Can be inherited from the operating system.
@host.domain	The domain of the host.
@host.environment Deprecated Use the `host_puppet_environment` variable instead.	The Puppet environment of the host.
@host.facts	Returns a Ruby hash of facts from Facter. For example to access the 'ipaddress' fact from the output, specify @host.facts['ipaddress'].
@host.grub_pass	Returns the host’s bootloader password.
@host.hostgroup	The host group of the host.
host_enc['parameters']	Returns a Ruby hash containing information on host parameters. For example, use host_enc['parameters']['lifecycle_environment'] to get the lifecycle environment of a host.
@host.image_build?	Returns `true` if the host is provisioned using an image.
@host.interfaces	Contains an array of all available host interfaces including the primary interface. See Section A.10, “Parsing arrays”.
@host.interfaces_with_identifier('IDs')	Returns array of interfaces with given identifier. You can pass an array of multiple identifiers as an input, for example @host.interfaces_with_identifier(['eth0', 'eth1']). See Section A.10, “Parsing arrays”.
@host.ip	The IP address of the host.
@host.location	The location of the host.
@host.mac	The MAC address of the host.
@host.managed_interfaces	Returns an array of managed interfaces (excluding BMC and bonded interfaces). See Section A.10, “Parsing arrays”.
@host.medium	The assigned operating system installation medium.
@host.name	The full name of the host.
@host.operatingsystem.family	The operating system family.
@host.operatingsystem.major	The major version number of the assigned operating system.
@host.operatingsystem.minor	The minor version number of the assigned operating system.
@host.operatingsystem.name	The assigned operating system name.
@host.operatingsystem.boot_files_uri(medium_provider)	Full path to the kernel and initrd, returns an array.
@host.os.medium_uri(@host)	The URI used for provisioning (path configured in installation media).
host_param('parameter_name')	Returns the value of the specified host parameter.
host_param_false?('parameter_name')	Returns `false` if the specified host parameter evaluates to false.
host_param_true?('parameter_name')	Returns `true` if the specified host parameter evaluates to true.
@host.primary_interface	Returns the primary interface of the host.
@host.provider	The compute resource provider.
@host.provision_interface	Returns the provisioning interface of the host. Returns an interface object.
@host.ptable	The partition table name.
@host.puppet_ca_server Deprecated Use the `host_puppet_ca_server` variable instead.	The Puppet CA server the host must use.
@host.puppetmaster Deprecated Use the `host_puppet_server` variable instead.	The Puppet server the host must use.
@host.pxe_build?	Returns `true` if the host is provisioned using the network or PXE.
@host.shortname	The short name of the host.
@host.sp_ip	The IP address of the BMC interface.
@host.sp_mac	The MAC address of the BMC interface.
@host.sp_name	The name of the BMC interface.
@host.sp_subnet	The subnet of the BMC network.
@host.subnet.dhcp	Returns `true` if a DHCP proxy is configured for this host.
@host.subnet.dns_primary	The primary DNS server of the host.
@host.subnet.dns_secondary	The secondary DNS server of the host.
@host.subnet.gateway	The gateway of the host.
@host.subnet.mask	The subnet mask of the host.
@host.url_for_boot(:initrd)	Full path to the initrd image associated with this host. Not recommended, as it does not interpolate variables.
@host.url_for_boot(:kernel)	Full path to the kernel associated with this host. Not recommended, as it does not interpolate variables, prefer boot_files_uri.
@provisioning_type	Equals to 'host' or 'hostgroup' depending on type of provisioning.
@static	Returns `true` if the network configuration is static.
@template_name	Name of the template being rendered.
grub_pass	Returns a bootloader argument to set the encrypted bootloader password, such as --md5pass=#{@host.grub_pass}.
ks_console	Returns a string assembled using the port and the baud rate of the host which can be added to a kernel line. For example console=ttyS1,9600.
root_pass	Returns the root password configured for the system.

The majority of common Ruby methods can be applied on host-specific variables. For example, to extract the last segment of the host’s IP address, you can use:

<% @host.ip.split('.').last %>

A.8. Kickstart-specific variables

The following variables are designed to be used within Kickstart provisioning templates.

Table A.3. Kickstart-specific variables
Name	Description
@arch	The host architecture name, same as @host.architecture.name.
@dynamic	Returns `true` if the partition table being used is a %pre script (has the #Dynamic option as the first line of the table).
@epel	A command which will automatically install the correct version of the epel-release RPM. Use in a %post script.
@mediapath	The full Kickstart line to provide the URL command.
@osver	The operating system major version number, same as @host.operatingsystem.major.

A.9. Conditional statements

In your templates, you might perform different actions depending on which value exists. To achieve this, you can use conditional statements in your ERB syntax.

In the following example, the ERB syntax searches for a specific host name and returns an output depending on the value it finds:

Example input

<% load_hosts().each_record do |host| -%>
<% if @host.name == "host1.example.com" -%>
<%      result="positive" -%>
<%  else -%>
<%      result="negative" -%>
<%  end -%>
<%= result -%>

Example rendering

host1.example.com
positive

A.10. Parsing arrays

While writing or modifying templates, you might encounter variables that return arrays. For example, host variables related to network interfaces, such as @host.interfaces or @host.bond_interfaces, return interface data grouped in an array. To extract a parameter value of a specific interface, use Ruby methods to parse the array.

Finding the correct method to parse an array

The following procedure is an example that you can use to find the relevant methods to parse arrays in your template. In this example, a report template is used, but the steps are applicable to other templates.

To retrieve the NIC of a content host, in this example, using the @host.interfaces variable returns class values that you can then use to find methods to parse the array.
Example input:
```
<%= @host.interfaces -%>
```
Example rendering:
```
<Nic::Base::ActiveRecord_Associations_CollectionProxy:0x00007f734036fbe0>
```
In the Create Template window, click the Help tab and search for the ActiveRecord_Associations_CollectionProxy and Nic::Base classes.
For ActiveRecord_Associations_CollectionProxy, in the Allowed methods or members column, you can view the following methods to parse the array:
```
[] each find_in_batches first map size to_a
```

For Nic::Base, in the Allowed methods or members column, you can view the following method to parse the array:

alias? attached_devices attached_devices_identifiers attached_to bond_options children_mac_addresses domain fqdn identifier inheriting_mac ip ip6 link mac managed? mode mtu nic_delay physical? primary provision shortname subnet subnet6 tag virtual? vlanid

To iterate through an interface array, add the relevant methods to the ERB syntax:

Example input:

<% load_hosts().each_record do |host| -%>
<%    host.interfaces.each do |iface| -%>
  iface.alias?: <%= iface.alias? %>
  iface.attached_to: <%= iface.attached_to %>
  iface.bond_options: <%= iface.bond_options %>
  iface.children_mac_addresses: <%= iface.children_mac_addresses %>
  iface.domain: <%= iface.domain %>
  iface.fqdn: <%= iface.fqdn %>
  iface.identifier: <%= iface.identifier %>
  iface.inheriting_mac: <%= iface.inheriting_mac %>
  iface.ip: <%= iface.ip %>
  iface.ip6: <%= iface.ip6 %>
  iface.link: <%= iface.link %>
  iface.mac: <%= iface.mac %>
  iface.managed?: <%= iface.managed? %>
  iface.mode: <%= iface.mode %>
  iface.mtu: <%= iface.mtu %>
  iface.physical?: <%= iface.physical? %>
  iface.primary: <%= iface.primary %>
  iface.provision: <%= iface.provision %>
  iface.shortname: <%= iface.shortname %>
  iface.subnet: <%= iface.subnet %>
  iface.subnet6: <%= iface.subnet6 %>
  iface.tag: <%= iface.tag %>
  iface.virtual?: <%= iface.virtual? %>
  iface.vlanid: <%= iface.vlanid %>
<%- end -%>

Example rendering:

host1.example.com
  iface.alias?: false
  iface.attached_to:
  iface.bond_options:
  iface.children_mac_addresses: []
  iface.domain:
  iface.fqdn: host1.example.com
  iface.identifier: ens192
  iface.inheriting_mac: 00:50:56:8d:4c:cf
  iface.ip: 10.10.181.13
  iface.ip6:
  iface.link: true
  iface.mac: 00:50:56:8d:4c:cf
  iface.managed?: true
  iface.mode: balance-rr
  iface.mtu:
  iface.physical?: true
  iface.primary: true
  iface.provision: true
  iface.shortname: host1.example.com
  iface.subnet:
  iface.subnet6:
  iface.tag:
  iface.virtual?: false
  iface.vlanid:

A.11. Example template snippets

Checking if a host has Puppet and Puppetlabs enabled

The following example checks if the host has the Puppet and Puppetlabs repositories enabled:

<%
pm_set = @host.puppetmaster.empty? ? false : true
puppet_enabled = pm_set || host_param_true?('force-puppet')
puppetlabs_enabled = host_param_true?('enable-puppetlabs-repo')
%>

Capturing major and minor versions of a host’s operating system

The following example shows how to capture the minor and major version of the host’s operating system, which can be used for package related decisions:

<%
os_major = @host.operatingsystem.major.to_i
os_minor = @host.operatingsystem.minor.to_i
%>

<% if ((os_minor < 2) && (os_major < 14)) -%>
...
<% end -%>

Importing snippets to a template

The following example imports the subscription_manager_registration snippet to the template and indents it by four spaces:

<%= indent 4 do
snippet 'subscription_manager_registration'
end %>

Conditionally importing a Kickstart snippet

The following example imports the kickstart_networking_setup snippet if the host’s subnet has the DHCP boot mode enabled:

<% subnet = @host.subnet %>
<% if subnet.respond_to?(:dhcp_boot_mode?) -%>
<%= snippet 'kickstart_networking_setup' %>
<% end -%>

Parsing values from host custom facts

You can use the host.facts variable to parse values from a host’s facts and custom facts. In this example luks_stat is a custom fact that you can parse in the same manner as dmi::system::serial_number, which is a host fact:

'Serial': host.facts['dmi::system::serial_number'],
'Encrypted': host.facts['luks_stat'],

In this example, you can customize the Applicable Errata report template to parse for custom information about the kernel version of each host:

<%-     report_row(
          'Host': host.name,
          'Operating System': host.operatingsystem,
          'Kernel': host.facts['uname::release'],
          'Environment': host.single_lifecycle_environment ? host.single_lifecycle_environment.name : nil,
          'Erratum': erratum.errata_id,
          'Type': erratum.errata_type,
          'Published': erratum.issued,
          'Applicable since': erratum.created_at,
          'Severity': erratum.severity,
          'Packages': erratum.package_names,
          'CVEs': erratum.cves,
          'Reboot suggested': erratum.reboot_suggested,
        ) -%>

Appendix A. Template writing reference

A.1. Accessing the template writing reference in the Satellite web UI

A.2. Using autocompletion in templates

A.3. Writing ERB templates

A.4. Troubleshooting ERB templates

A.5. Generic Satellite-specific macros

A.6. Template macros

A.7. Host-specific variables

A.8. Kickstart-specific variables

A.9. Conditional statements

A.10. Parsing arrays

A.11. Example template snippets

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