open-nomad/.circleci/README.md

# How to use CircleCI multi-file config

This README and the Makefile should be in your `.circleci` directory,
in the root of your repository.
All path references in this README assume we are in this `.circleci` directory.

The `Makefile` in this directory generates `./config.yml` in CircleCI 2.0 syntax,
from the tree rooted at `./config/`, which contains files in CircleCI 2.0 or 2.1 syntax.


## Quickstart

The basic workflow is:

- Edit source files in `./config/`
- When you are done, run `make ci-config` to update `./config.yml`
- Commit this entire `.circleci` directory, including that generated file together.
- Run `make ci-verify` to ensure the current `./config.yml` is up to date with the source.

When merging this `.circleci` directory:

- Do not merge the generated `./config.yml` file, instead:
- Merge the source files under `./config/`, and then
- Run `make ci-config` to re-generate the merged `./config.yml`

And that's it, for more detail, read on!


## How does it work, roughly?

CircleCI supports [generating a single config file from many],
using the `$ circleci config pack` command.
It also supports [expanding 2.1 syntax to 2.0 syntax]
using the `$ circleci config process` command.
We use these two commands, stitched together using the `Makefile`
to implement the workflow.

[generating a single config file from many]: https://circleci.com/docs/2.0/local-cli/#packing-a-config
[expanding 2.1 syntax to 2.0 syntax]: https://circleci.com/docs/2.0/local-cli/#processing-a-config


## Prerequisites

You will need the [CircleCI CLI tool] installed and working,
at least version `0.1.5607`.
You can [download this tool directly from GitHub Releases].

```
$ circleci version
0.1.5607+f705856
```

[CircleCI CLI tool]: https://circleci.com/docs/2.0/local-cli/
[download this tool directly from GitHub Releases]: https://github.com/CircleCI-Public/circleci-cli/releases


## Updating the config source

Before making changes, be sure to understand the layout
of the `./config/` file tree, as well as circleci 2.1 syntax.
See the [Syntax and layout] section below.

To update the config, you should edit, add or remove files
in the `./config/` directory,
and then run `make ci-config`.
If that's successful,
you should then commit every `*.yml` file in the tree rooted in this directory.
That is: you should commit both the source under `./config/`
and the generated file `./config.yml` at the same time, in the same commit.
The included git pre-commit hook will help with this.
Do not edit the `./config.yml` file directly, as you will lose your changes
next time `make ci-config` is run.

[Syntax and layout]: #syntax-and-layout


### Verifying `./config.yml`

To check whether or not the current `./config.yml` is up to date with the source
and valid, run `$ make ci-verify`.
Note that `$ make ci-verify` should be run in CI,
in case not everyone has the git pre-commit hook set up correctly.


#### Example shell session

```sh
$ make ci-config
config.yml updated 
$ git add -A . # The -A makes sure to include deletions/renames etc.
$ git commit -m "ci: blah blah blah"
Changes detected in .circleci/, running 'make -C .circleci ci-verify'
--> Generated config.yml is up to date!
--> Config file at config.yml is valid.
```


### Syntax and layout

It is important to understand the layout of the config directory.
Read the documentation on [packing a config] for a full understanding
of how multiple YAML files are merged by the circleci CLI tool.

[packing a config]: https://circleci.com/docs/2.0/local-cli/#packing-a-config

Here is an example file tree (with comments added afterwards):

```sh
$ tree . 
.
├── Makefile
├── README.md # This file.
├── config    # The source code for config.yml is rooted here.
│   ├── @config.yml # Files beginning with @ are treated specially by `circleci config pack`
│   ├── commands    # Subdirectories of config become top-level keys.
│   │   └── go_test.yml  # Filenames (minus .yml) become top-level keys under
│   │   └── go_build.yml # their parent (in this case "commands").
│   │                    # The contents of go_test.yml therefore are placed at: .commands.go_test:
│   └── jobs             # jobs also becomes a top-level key under config...
│       ├── build.yml    # ...and likewise filenames become keys under their parent.
│       └── test.yml
└── config.yml # The generated file in 2.0 syntax.
```

About those `@` files... Preceding a filename with `@`
indicates to `$ circleci config pack` that the contents of this YAML file
should be at the top-level, rather than underneath a key named after their filename.
This naming convention is unfortunate as it breaks autocompletion in bash,
but there we go.