Read Environment Variables

It might surprise you to learn that postgres is probably not going to be the password for your production database.

To have something that can work in development as well as where you deploy it, you should read your configuration using environment variables.

• Add dotenv-java to your deps.edn.

  There are more solutions to this - like direnv or bash profiles - but this is the one we are going with for the moment.

  {:paths ["src"]
   :deps {org.clojure/clojure {:mvn/version "1.12.0"}
          ring/ring {:mvn/version "1.13.0"}
          metosin/reitit-ring {:mvn/version "0.7.2"}
          org.clojure/tools.logging {:mvn/version "1.3.0"}
          org.slf4j/slf4j-simple {:mvn/version "2.0.16"}
          hiccup/hiccup {:mvn/version "2.0.0-RC3"}
          com.github.seancorfield/next.jdbc {:mvn/version "1.3.955"}
          org.postgresql/postgresql {:mvn/version "42.7.4"}
          com.zaxxer/HikariCP {:mvn/version "6.0.0"}
          io.github.cdimascio/dotenv-java {:mvn/version "3.0.2"}}
   :aliases {:dev {:extra-paths ["dev" "test"]
                   :extra-deps {nrepl/nrepl {:mvn/version "1.3.0"}
                                lambdaisland/kaocha {:mvn/version "1.91.1392"}}}
             :format {:deps {dev.weavejester/cljfmt {:mvn/version "0.13.0"}}}
             :lint   {:deps {clj-kondo/clj-kondo {:mvn/version "2024.09.27"}}}}}

• Add an env component to the system.

  This is all the other components will read from as they start up to access environment variables. In this way we can make whatever is in .env be available as if it was an environment variable in dev and use real environment variables when we deploy.

  (ns example.system
    (:require [example.routes :as routes]
              [next.jdbc.connection :as connection]
              [ring.adapter.jetty :as jetty])
    (:import (com.zaxxer.hikari HikariDataSource)
             (io.github.cdimascio.dotenv Dotenv)
             (org.eclipse.jetty.server Server)))
  
  (set! *warn-on-reflection* true)
  
  (defn start-env
    []
    (Dotenv/load))
  
  (defn start-db
    []
    (connection/->pool HikariDataSource
                       {:dbtype "postgres"
                        :dbname "postgres"
                        :username "postgres"
                        :password "postgres"}))
  
  (defn stop-db
    [db]
    (HikariDataSource/.close db))
  
  (defn start-server
    [system]
    (jetty/run-jetty
     (partial #'routes/root-handler system)
     {:port 9999
      :join? false}))
  
  (defn stop-server
    [server]
    (Server/.stop server))
  
  (defn start-system
    []
    (let [system-so-far {::env (start-env)}
          system-so-far (merge system-so-far {::db (start-db)})]
      (merge system-so-far {::server (start-server system-so-far)})))
  
  (defn stop-system
    [system]
    (stop-db (::db system))
    (stop-server (::server system)))

• Read the server PORT, POSTGRES_USERNAME, POSTGRES_PASSWORD from the environment

  First add those values to the .env file.

  POSTGRES_USERNAME=postgres
  POSTGRES_PASSWORD=postgres
  PORT=9999

  Then read values off the env component when making other components.

  (ns example.system
    (:require [example.routes :as routes]
              [next.jdbc.connection :as connection]
              [ring.adapter.jetty :as jetty])
    (:import (com.zaxxer.hikari HikariDataSource)
             (io.github.cdimascio.dotenv Dotenv)
             (org.eclipse.jetty.server Server)))
  
  (set! *warn-on-reflection* true)
  
  (defn start-env
    []
    (Dotenv/load))
  
  (defn start-db
    [{::keys [env]}]
    (connection/->pool HikariDataSource
                       {:dbtype "postgres"
                        :dbname "postgres"
                        :username (Dotenv/.get env "POSTGRES_USERNAME")
                        :password (Dotenv/.get env "POSTGRES_PASSWORD")}))
  
  (defn stop-db
    [db]
    (HikariDataSource/.close db))
  
  (defn start-server
    [{::keys [env] :as system}]
    (jetty/run-jetty
     (partial #'routes/root-handler system)
     {:port  (parse-long (Dotenv/.get env "PORT"))
      :join? false}))
  
  (defn stop-server
    [server]
    (Server/.stop server))
  
  (defn start-system
    []
    (let [system-so-far {::env (start-env)}
          system-so-far (merge system-so-far {::db (start-db system-so-far)})]
      (merge system-so-far {::server (start-server system-so-far)})))
  
  (defn stop-system
    [system]
    (stop-db (::db system))
    (stop-server (::server system)))

  I know, I can hear your Clojure senses tingling. Isn't env conceptually just a map? Why are we using a Java library for this?

  It boils down to two factors.

  1. dotenv-java is more well maintained than Clojure equivalents. Not that things can't be "done" and not require further maintenance. If you have a library you prefer, have at it.
  2. It's conceptually a map, but we only are going to be reading it here and it being an opaque Java object has the nice benefit of its toString implementation not leaking sensitive info by default.

• Add an env function to your user namespace

  (ns user
    (:require [example.system :as system]))
  
  (def system nil)
  
  (defn start-system!
    []
    (if system
      (println "Already Started")
      (alter-var-root #'system (constantly (system/start-system)))))
  
  (defn stop-system!
    []
    (when system
      (system/stop-system system)
      (alter-var-root #'system (constantly nil))))
  
  (defn restart-system!
    []
    (stop-system!)
    (start-system!))
  
  (defn server
    []
    (::system/server system))
  
  (defn db
    []
    (::system/db system))
  
  (defn env
    []
    (::system/env system))