Configuration

Most of your app's configuration is stored in the resources/config.edn file:

{:biff/base-url #profile {:prod #join ["https://" #biff/env DOMAIN]
                          :default "http://localhost:8080"}
 :biff/host     #profile {:dev "0.0.0.0"
                          :default "localhost"}
 :biff/port     8080

 :biff.xtdb/dir      "storage/xtdb"
 :biff.xtdb/topology #keyword #or [#profile {:prod #biff/env "PROD_XTDB_TOPOLOGY"
                                             :default #biff/env "XTDB_TOPOLOGY"}
                                   "standalone"]
 :biff.xtdb.jdbc/jdbcUrl #biff/secret "XTDB_JDBC_URL"
...

This file is parsed with Aero. The biff/use-aero-config component sets the profile to the value of the BIFF_PROFILE environment variable. In production, BIFF_PROFILE is set to prod; during development, it's set to dev. You can add new profiles if needed, like a :ci profile for running automated tests.

biff/use-aero-config merges your config into the system map. Since the system map is in turn merged with incoming requests, you can read config values in your request handlers like so:

(defn hello [{:keys [biff/base-url] :as ctx}]
  [:html
   [:body
    [:p "This website is located at " base-url]]])

(def module
  {:routes [["/hello" {:get hello}]]})

Configuration is only read by biff/use-aero-config during app startup, so if you modify resources/config.edn or config.env during development, you'll need to call com.example/refresh for the changes to take effect.

Secrets

Secrets should always be kept in the config.env file, which isn't checked into git:

MAILERSEND_API_KEY=abc123
...

The biff/use-aero-secrets component sets the :biff/secret key in the system map to a function. That function takes a keyword and returns the associated secret. For example, if your config and secrets files have the following contents:

# config.env
MAILERSEND_API_KEY=abc123

;; config.edn
{:mailersend/api-key #biff/secret MAILERSEND_API_KEY ...

then the following handler would print abc123 to the console:

(defn hello [{:keys [biff/secret] :as ctx}]
  (println (secret :mailersend/api-key))
  ...)

(def module
  {:routes [["/hello" {:get hello}]]})

This is done so that your secrets won't be exposed if you serialize your system map (e.g. by printing it to your logs).

If you need to provide different values for a secret in different environments, you can specify separate environment variable names in resources/config.edn:

:stripe/api-key #profile {:prod "STRIPE_API_KEY_PROD"
                          :dev "STRIPE_API_KEY_TEST"}

Customizing config

If you need to store your config and/or secrets in some other way, you can replace biff/use-aero-config with a custom component:

(defn use-custom-config [system]
  (let [config ...]
    (merge system config)))

(def components
  [use-custom-config
   biff/use-xtdb
   ...])

use-custom-config can load configuration in whatever way you'd like it to, as long as it satisfies two conditions:

:biff/secret is set to a 1-arg function that takes a keyword and returns the associated secret value.
Non-secret config is merged directly into the system map.