Consider launching dockerized cljdoc from jar

[lread]

Currently

Cljdoc is launched in production within its docker container via clojure.

Idea

Instead, launch cljdoc from a stand alone jar via java.

Why?

Faster startup time in production, but perhaps more interesting, faster times when using running cljdoc locally via docker.

I did a wee adhoc test from the command line (not involving docker).
I wait about 15s until first log line output when launching via:

clojure -M -m cljdoc.server.system

Versus about 5s to first log line output when launching via a prebuilt stand-alone jar which in my local test was via:

java -jar target/cljdoc-1.2.3-leetest-standalone.jar

This jar was built via the following quickly-hacked-together build.clj:

(ns build
  (:require [clojure.tools.build.api :as b]))

(def lib 'cljdoc/cljdoc)
(def version "1.2.3-leetest")
(def class-dir "target/classes")
(def basis (b/create-basis {:project "deps.edn" :aliases [:cli]}))
(def uber-file (format "target/%s-%s-standalone.jar" (name lib) version))

(defn clean [_]
  (b/delete {:path "target"}))

(defn uber [_]
  (clean nil)
  (b/copy-dir {:src-dirs ["src" "resources" "resources-compiled"]
               :target-dir class-dir})
  (b/compile-clj {:basis basis
                  :src-dirs ["src"]
                  :class-dir class-dir})
  (b/uber {:class-dir class-dir
           :uber-file uber-file
           :basis basis
           :main 'cljdoc.server.system}))

Impacts

We currently support running cljdoc locally via the production cljdoc docker image.

This can use a different main entry point than the production server launch does, for example for ingesting local docs.

As far I understand things, a jar only easily supports a single main entry point.

So, if we entertained this change, we'd likely move to a single main entry point.

Whatcha think?

I'm sure I haven't thought of a thing or two, happy to hear what you, dear reader, think.

[lread]

Or... maybe look at jlink and CDS for launch speed.

This would add some complexity to the docker build so we'd have to measure the benefit.

[lread]

Of interest, you can invoke multiple different mains from a jar by using -cp instead of -jar.

Nic example from @seancorfield on slack:

(~/clojure/mains)-(!2016)-> cat src/multi/another.clj
(ns multi.another
  (:gen-class))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (println "I'm another main!"))

Thu Feb 09 11:18:09
(~/clojure/mains)-(!2017)-> cat src/multi/mains.clj
(ns multi.mains
  (:gen-class))

(defn greet
  "Callable entry point to the application."
  [data]
  (println (str "Hello, " (or (:name data) "World") "!")))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (greet {:name (first args)}))

Thu Feb 09 11:18:12
(~/clojure/mains)-(!2018)-> java -jar target/net.clojars.multi/mains-0.1.0-SNAPSHOT.jar
Hello, World!

Thu Feb 09 11:18:22
(~/clojure/mains)-(!2019)-> java -jar target/net.clojars.multi/mains-0.1.0-SNAPSHOT.jar argument
Hello, argument!

Thu Feb 09 11:18:28
(~/clojure/mains)-(!2020)-> java -cp target/net.clojars.multi/mains-0.1.0-SNAPSHOT.jar multi.mains
Hello, World!

Thu Feb 09 11:18:48
(~/clojure/mains)-(!2021)-> java -cp target/net.clojars.multi/mains-0.1.0-SNAPSHOT.jar multi.mains argument
Hello, argument!

Thu Feb 09 11:18:52
(~/clojure/mains)-(!2022)-> java -cp target/net.clojars.multi/mains-0.1.0-SNAPSHOT.jar multi.another
I'm another main!

Thu Feb 09 11:19:02
(~/clojure/mains)-(!2023)->