exvar

Local repository specific application configuration management framework.

Motivation (Background)

Some configurations depend on the environment where their application runs so it is diffcult to manage them by version control system(vcs).

For example, the port number application uses depends on the environment. To hardcode the port number in the configuration file has trouble when the port number is used by another process.

One of the approaches to deal with this problem are to use environment variables. There are some useful tools to manage the environment variables (such as direnv).

But unfortunately some configuration files can't refer the environment variables. In addition, many such tools doesn't provide the template file manages the environment specific configurations and their default values and description about them.

Especially for developers who have joined your project newly, it is important to know the list of the environment specific configurations and their default values and descriptions about them.

By exvar you can manage them as code.

Note that we refer to the environment variable management tools in the above, but exvar doesn't conflict with them at all. Rather exvar can complement them.

Why do we call exvar a "framework"?

exvar provides the consistent and generic way to manage the environment specific configurations in the project using vcs. You don't need to be worried about how to manage them, and don't need to develop your own rules and tools any more.

Terms

There are some exvar specific terms.

• base file (.exvar.base.yml)
• user file (.exvar.yml)
• variable (placeholder)
• source file (template)
• destination file

base file (.exvar.base.yml)

This file should be managed by vcs. This file is required.

---
config:
  # (default source file name) = default_prefix + (destination filename) + default_suffix
  default_prefix: .
  default_suffix:
files:
  # relative path from the directory where the base file exists
  <destination file path>:
    [src: source file's relative path from the parent directory of the base file]
    [comment: comment about the destination file]
    vars:
      # variable name format is free
      <variable name>:
        [comment: comment about the variable]
        # If the "value" field doesn't exist, the value must be set in the user file.
        # If it is null, it is treated as the empty string
        [value: the variable value]

user file (.exvar.yml)

This file should not be managed by vcs. This file is not required if all variables have default values in the base file.

---
files:
  <destination file path>:
    <variable name>:
      [comment: description about the variable's value]
      # If the "value" field doesn't exist,
      # the value must be set in the base file.
      # If the value of it is null, it is treated as the empty string
      [value: null]

variable

variable name

The format of variable name is free. It is important that exvar doesn't a template engine. exvar simply replace variable names to variable values.

variable value

The type of the variable value is string. If the type of the value of the "value" field in the base file and user file is not scalar (such as list or dict etc), the error will have occured. If the type of it is int, the value is coverted to str. If it is null, it is treated as the empty string.

source file

This file should be managed by vcs. The format of source files is free. It is important that exvar doesn't a template engine. exvar simply replace your defined placeholders(arbitary strings) to actual values.

destination file

This file shouldn't be managed by vcs. This is generated automatically by exvar run command, so you shouldn't edit this directly.

Use case 1. Vagrantfile and ssh config file

We describe how to use exvar using a concrete use case.

Assume that you use vagrant and vagrant's private network and manage ssh config as follow.

# Vagrantfile
Vagrant.configure("2") do |config|
  config.vm.network "private_network", ip: "192.168.50.4"
end

# ssh_config
Host vm
  Hostname 192.168.50.4
  User vagrant

Then let's manage the private ip address by exvar.

$ mv ssh_config .tmpl.ssh_config
$ mv Vagrantfile .tmpl.Vagrantfile
$ exvar init
$ vi .tmpl.ssh_config
$ vi .tmpl.Vagrantfile
$ vi .exvar.base.yml

# .tmpl.Vagrantfile
Vagrant.configure("2") do |config|
  config.vm.network "private_network", ip: "$[vm ip]"
end

# .tmpl.ssh_config
Host vm
  Hostname $[vm ip]
  User vagrant

# .exvar.base.yml
config:
  default_prefix: .tmpl.
  default_suffix:
files:
  ssh_config:
    vars:
      $[vm ip]:
        value: 192.168.50.4
  Vagrantfile:
    vars:
      $[vm ip]:
        value: 192.168.50.4

You can validate the base file and user file and source file by exvar check command.

$ exvar check

Finally, you can create the destination file (in this case "Vagrantfile" and "ssh_config") by exvar run command.

$ exvar run

In the above the default private ip address is "192.168.50.4". If you want to change the private ip address in your local repository, set the value in the .exvar.yml and run exvar run again.

# .exvar.yml
files:
  ssh_config:
    vars:
      $[vm ip]:
        value: 192.168.30.1
  Vagrantfile:
    vars:
      $[vm ip]:
        value: 192.168.30.1

$ exvar check
$ exvar run

You should add destination files and user file to .gitignore.

# .gitignore
Vagrantfile
ssh_config
.exvar.yml

Requirements

• Python 3

Install

$ pip install exvar

Usage

$ exvar -v, --version         Print the exvar version number and exit.
$ exvar --help                Show the help message and exit.
$ exvar init                  Create .exvar.base.yml and .exvar.yml if they don't exist.
$ exvar check [--check-dest]  Validate the base file and user file and source files and destination files.
$ exvar run                   Create or update dest files.
$ exvar ls-dest               List destination file paths.
$ exvar root-path             Print the absolute path of the parent directory of the base file.

Comparison with similar softwares

Unfortunately we can't find similar softwares. Please issue if you find them.

Contributing

1. Fork (https://github.com/suzuki-shunsuke/exvar.py/fork)
2. Create a feature branch
3. Commit your changes
4. Rebase your local changes against the master branch
5. Run test suite with the pytest command and confirm that it passes
6. Create a new Pull Request

License

MIT

Author

Suzuki Shunsuke