Configuration

Environment Variables

The configuration is represented by a map. the map is constructed by aggregating variables from multiple sources in the environment. The default sources include EDN configuration and shell variables.

EDN Based Configuration

The library will first look for a config.edn file on the resource path. This will be used as the base configuration for the application. An external configuration file can be specified using the conf environment variable at runtime, e.g: export CONF="prod-config.edn".

The configuration placed in the configuration file should consist of a map such as the following:

{:port 4000
 :host "127.0.0.1"}

This configuration will be merged on top of the configuration found in the environment. The library uses a deep merge strategy, so any nested structures will be merged intelligently.

Managing Environment Variables

Environment variable names are converted into Clojure style keywords. These variables are parsed using the following strategy:

  • PORT=3000 -> {:port 3000}
  • NREPL_PORT=7000 - {:nrepl-port 7000}
  • DATABASE_URL="jdbc:h2:./guestbook_dev.db" -> {:database-url "jdbc:h2:./guestbook_dev.db"}
  • IO__HTTP_MAX_CONNECTIONS="{:value 10}" -> {:io {:http-max-connections {:value 10}}}

Note that the _ is converted to -, while __ is used to indicate nesting for shell variables. These conventions can be mixed as seen with IO__HTTP_MAX_CONNECTIONS.

The library will attempt to parse variables in the following order:

  • attempt to parse numeric value
  • attempt to parse boolean
  • variables that start with a letter are treated as strings
  • any other variables are parsed as EDN

Configuration Order

The environment configuration will be read as the default.

Next, the library will look for the conf environment variable. When present, it will attempt to read configuration from the file pointed to by this variable.

When the conf environment variable is not present, the library will look for a file called config.edn at the location where the app was run.

When a configuration file is found, it will be deep merged on top of the configuration read from the envrionment.

Documentation