# Fettle
Runs health-check functions periodically, and aggregates health status reports.
(AKA Elixir implementation of FT Health-Check standard).
[](http://inch-ci.org/github/Financial-Times/fettle) [](https://travis-ci.org/Financial-Times/fettle)
> **fettle**
*noun* - "his best players were in fine fettle": shape, trim, fitness, physical fitness, health, state of health; condition, form, repair, state of repair, state, order, working order, way; informal: kilter; British informal: nick.
This library implents an asynchronous periodic check mechanism, and defines a way of configuring checks, and getting reports in a particular format. It is intended for use with monitoring and dashboards.
Ships with the [FT Health Check V1](FTHealthcheckstandard.pdf) schema format for report generation, but the schema is configurable.
## See also
* [`fettle_plug`](https://github.com/Financial-Times/fettle_plug) - integration with [Plug](https://github.com/elixir-lang/plug) to expose to HTTP.
* [`fettle_checks`](https://github.com/Financial-Times/fettle_checks) - a small library of commonly useful checks.
## Getting Started
### Installation
Add a dependency in your `mix.exs` config:
For the bleeding edge:
```elixir
def deps do
[{:fettle, github: "Financial-Times/fettle"}]
end
```
Fettle is an OTP application, and in Elixir 1.4+, will be started with other applications through Elixir's auto-detection of OTP apps in dependencies.
### Defining checks
The [`fettle_checks`](https://github.com/Financial-Times/fettle_checks) module provides pre-canned checks, but to write your own, implement a module with the `Fettle.Checker` `@behaviour` that runs a check, and returns a `Fettle.Check.Result` struct:
```elixir
defmodule MyCheck do
@behaviour Fettle.Checker
def check(args) do
case do_check(args) do # assume do_check/1 does something useful!
:ok ->
{Fettle.Check.Result.ok(), args}
{:error, message} ->
{Fettle.Check.Result.error(message), args}
end
end
end
```
Then configure this check, with some required metadata, in the `:fettle` configuration:
```elixir
config :fettle,
system_code: "my_app", # required (for reports)
checks: [
%{
name: "my-check",
panic_guide_url: "https://...",
business_impact: "...",
technical_summary: "..."
checker: MyCheck, # name of our check module
args: "url_or_something" # arguments to the checker module (optional)
},
...
]
```
On application start-up, Fettle will start running your check, by default every 30 seconds, and you can retrieve the results using `Fettle.report/1`.
[`fettle_plug`](https://github.com/Financial-Times/fettle_plug) can then be used to expose the results over an HTTP end-point.
See module docs for full details.
