yogthos / Config

yogthos/config

A library for managing configuration using environment variables and EDN configuration files.

The configuration is resolved in the following order, the variables found in later configurations will replace those declared earlier:

1. config.edn on the classpath
2. .lein-env file in the project directory
3. .boot-env file in the project directory
4. EDN file specified using the config environment variable
5. Environment variables
6. Java System properties

The library parses configuration keys into Clojure keywords with names lowercased, then _ and . characters converted to dashes, e.g:

• foo_bar -> foo-bar
• Foo_bar -> foo-bar
• Foo.BAR -> foo-bar

The values are parsed using the following strategy:

1. [0-9]+ -> number
2. ^(true|false)$ -> boolean
3. \w+ -> string
4. try parse as EDN, and return the original value as the default

following environment variables:

* BOOL=true
* text="true"
* number=15
* quoted-number="12"
* edn_string="{:foo :bar :baz [1 2 \"foo\"]}"
* unparsed.text="some text here"

are translated as:

* :bool          true,
* :text          "true",
* :number        15,
* :quoted-number "12",
* :edn-string    {:foo :bar, :baz [1 2 "foo"]},
* :unparsed-text "some text here"

Installation

Include the following dependency in your project.clj file:

Usage

external configuration

In most cases you'll likely want to specify the configuration file using the config environment variable. We will add the dependency to our project.clj file and specify the configuration file location using :jvm-opts:

(defproject edn-config-test "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.10.0"]
                 [yogthos/config <VERSION>]]
  ;; configuration will be read from the dev-config.edn file               
  :jvm-opts ["-Dconfig=dev-config.edn"]               
  :main edn-config-test.core)

embedded configuration

In some cases you may wish to package configuration in the jar along with the application. In this case the config.edn file must be present on the classpath.

Let's take a look at setting up separate configurations for development and production by adding profiles to project.clj. We'll create dev and prod profiles each pointing to a different resource path containing the desired configuration.

First, we'll need to create a config folder in the root of the project. Under the config we will create dev and prod folders. Each of this will contain a file called config.edn.

We'll create a development configuration in config/dev/config.edn:

{:db "jdbc:sqlite:dev.db"}

and a production configuration in config/prod/config.edn:

{:db "jdbc:sqlite:prod.db"}

Next, we will add the dependency and the profiles to our project.clj:

(defproject edn-config-test "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.10.0"]
                 [yogthos/config <VERSION>]]
  :profiles {:prod {:resource-paths ["config/prod"]}
             :dev  {:resource-paths ["config/dev"]}}
  :main edn-config-test.core)

Accessing the configuration

We can now access the config variables the config.edn found under the resource path specified in the profile. There are two ways of doing this. We can load a version of config defined as config.core/env:

(ns edn-config-test.core
  (:require [config.core :refer [env]])
  (:gen-class))

(defn -main []
  (println (:db env)))

The config in env can be reloaded at runtime by calling the reload-env function.

Alternatively, we can call the config.core/load-env explicitly to manage the state of the config in the app. For example, if we use the mount library, we could write the following:

(ns edn-config-test.core
  (:require [mount.core :refer [defstate]]
            [config.core :refer [load-env]])
  (:gen-class))

(defstate env
  :start (load-env))

  (defn -main []
    (mount.core/start)
    (println (:db env)))    

Packaging for release

The application can be packaged using a specific profile by using the Leiningen with-profile option. For example, if we wanted to package with the prod profile then we'd run the following:

lein with-profile prod uberjar

The resulting jar will contain the config found in config/prod/config.edn in case an embedded configuration was used:

java -jar target/edn-config-test.jar
=> jdbc:sqlite:prod.db

Alternatively, we can create a file called custom-config.edn that looks as follows:

{:db "jdbc:sqlite:prod-custom.db"}

Then we can start the app and pass it the config environment variable pointing to the location of the file:

java -Dconfig="custom-config.edn" -jar target/edn-config-test.jar
=> jdbc:sqlite:prod-custom.db

Attributions

The yogthos/config project is based on the environ library.

License

Distributed under the Eclipse Public License, the same as Clojure.