genericize dockerfile writer

To maximize the benefit of caching, we need to allow the Dockerfile to be generated dynamically to minimize the number of file dependencies per step. Prepare to do this
by allowing dockerfile_writer.rb to accept arguments.

refs DE-183

Test Plan:
1. Ensure that ubuntu.development.Dockerfile doesn’t have any changes when run locally
2. Ensure that ubuntu.production.Dockerfile doesn’t have any changes when run locally

Change-Id: I8b4ba10b5929c2ee60c5c3537b70f606c8ea1d52
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/244604
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: James Butters <jbutters@instructure.com>
QA-Review: Aaron Ogata <aogata@instructure.com>
Product-Review: Aaron Ogata <aogata@instructure.com>

build/dockerfile_writer.rb

@@ -17,14 +17,17 @@
 # with this program. If not, see <http://www.gnu.org/licenses/>.
 
 require "erubi"
+require "optparse"
 require_relative "./docker_utils"
 
 class DockerfileWriter
-  attr_reader :env, :compose_files
+  attr_reader :env, :compose_files, :in_file, :out_file
 
-  def initialize(env:, compose_files:)
+  def initialize(env:, compose_files:, in_file:, out_file:)
     @env = env
     @compose_files = compose_files
+    @in_file = in_file
+    @out_file = out_file
   end
 
   def production?
@@ -39,13 +42,13 @@ class DockerfileWriter
     <<~STR
       # GENERATED FILE, DO NOT MODIFY!
       # To update this file please edit the relevant template and run the generation
-      # task `build/dockerfile_writer.rb`
+      # task `build/dockerfile_writer.rb --env #{env} --compose-file #{compose_files.join(',')} --in #{in_file} --out #{out_file}`
     STR
   end
 
-  def run(filename)
-    File.open(filename, "w") do |f|
-      f.write eval(Erubi::Engine.new(File.read("build/ubuntu.Dockerfile.template")).src, nil, "build/ubuntu.Dockerfile.template")
+  def run()
+    File.open(out_file, "w") do |f|
+      f.write eval(Erubi::Engine.new(File.read(in_file)).src, nil, in_file)
     end
   end
 
@@ -63,12 +66,26 @@ class DockerfileWriter
   end
 end
 
-DockerfileWriter.new(
-  env: "development",
-  compose_files: ["docker-compose.yml", "docker-compose.override.yml"]
-).run("ubuntu.development.Dockerfile")
+options = {}
 
-DockerfileWriter.new(
-  env: "production",
-  compose_files: ["docker-compose.yml"]
-).run("ubuntu.production.Dockerfile")
+OptionParser.new do |opts|
+  opts.banner = "Usage: dockerfile_writer.rb [options]"
+
+  opts.on("--env [ENVIRONMENT]", String, "Dockerfile Environment") do |v|
+    options[:env] = v
+  end
+
+  opts.on("--compose-file x,y,z", Array, "List of compose files") do |v|
+    options[:compose_files] = v
+  end
+
+  opts.on("--in [FILENAME]", String, "Input Template File") do |v|
+    options[:in_file] = v
+  end
+
+  opts.on("--out [FILENAME]", String, "Output File") do |v|
+    options[:out_file] = v
+  end
+end.parse!
+
+DockerfileWriter.new(**options).run()

ubuntu.development.Dockerfile

@@ -1,6 +1,6 @@
 # GENERATED FILE, DO NOT MODIFY!
 # To update this file please edit the relevant template and run the generation
-# task `build/dockerfile_writer.rb`
+# task `build/dockerfile_writer.rb --env development --compose-file docker-compose.yml,docker-compose.override.yml --in build/ubuntu.Dockerfile.template --out ubuntu.development.Dockerfile`
 
 # For documentation, please check doc/docker/README.md in
 # this local repo which is also published at:

ubuntu.production.Dockerfile

@@ -1,6 +1,6 @@
 # GENERATED FILE, DO NOT MODIFY!
 # To update this file please edit the relevant template and run the generation
-# task `build/dockerfile_writer.rb`
+# task `build/dockerfile_writer.rb --env production --compose-file docker-compose.yml --in build/ubuntu.Dockerfile.template --out ubuntu.production.Dockerfile`
 
 # For documentation, please check doc/docker/README.md in
 # this local repo which is also published at: