Creating an application from a template

Template structure

Application templates are directories with files.

The main file of a template is its manifest. It defines how the applications are instantiated from this template.

A template manifest is a YAML file named MANIFEST.yaml. It can contain the following sections:

• description – the template description.
• vars – template variables.
• pre-hook and post-hook – paths to executables to run before and after the template instantiation.
• include – a list of files to keep in the application directory after instantiation. If this section is omitted, the application will contain all template files and directories.

All sections are optional.

Example:

description: Template description
vars:
  - prompt: User name
    name: user_name
    default: admin
    re: ^\w+$

  - prompt: Retry count
    default: "3"
    name: retry_count
    re: ^\d+$
pre-hook: ./hooks/pre-gen.sh
post-hook: ./hooks/post-gen.sh
include:
  - init.lua
  - instances.yml

Files and directories of a template are copied to the application directory according to the include section of the manifest (or its absence).

There is a special file type *.tt.template. The content of such files is adjusted for each application with the help of template variables. During the instantiation, the variables in these files are replaced with provided values and the *.tt.template extension is removed.

Variables

Templates variables are replaced with their values provided upon the instantiation.

All templates have the name variable. Its value is taken from the --name option.

To add other variables, define them in the vars section of the template manifest. A variable can have the following attributes:

• prompt: a line of text inviting to enter the variable value in the interactive mode. Required.
• name: the variable name. Required.
• default: the default value. Optional.
• re: a regular expression that the value must match. Optional.

Example:

vars:
  - prompt: Cluster cookie
    name: cluster_cookie
    default: cookie
    re: ^\w+$

Variables can be used in all file names and the content of *.tt template files.

To use a variable, enclose its name with a period in the beginning in double curly braces: {{.var_name}} (as in the Golang text templates syntax).

Examples:

• init.lua.tt.template file:

  local app_name = {{.name}}
  local login = {{.user_name}}
  

• A file name {{.user_name}}.txt

Variables receive their values during the template instantiation. By default, tt create asks you to provide the values interactively. You can use the -s (or --non-interactive) option to disable the interactive input. In this case, the values are searched in the following order:

• In the --var option. Pass a string of the var=value format after the --var option. You can pass multiple variables, each after a separate --var option:

  $ tt create template app --var user_name=admin
  

• In a file. Specify var=value pairs in a plain text file, each on a new line, and pass it as the value of the --vars-file option:

  $ tt create template app --vars-file variables.txt
  

  variables.txt can look like this:

  user_name=admin
  password=p4$$w0rd
  version=2
  

If a variable isn’t initialized in any of these ways, the default value from the manifest is used.

You can combine different ways of passing variables in a single call of tt create.