Expose phx.new dev.exs to host if we're in a docker env

installer/lib/mix/tasks/phx.new.ex

@@ -53,7 +53,7 @@ defmodule Mix.Tasks.Phx.New do
 
     * `--no-html` - do not generate HTML views
 
-    * `--no-live` - comment out LiveView socket setup in your Endpoint 
+    * `--no-live` - comment out LiveView socket setup in your Endpoint
       and assets/js/app.js. Automatically disabled if --no-html is given
 
     * `--no-mailer` - do not generate Swoosh mailer files
@@ -142,6 +142,7 @@ defmodule Mix.Tasks.Phx.New do
     mailer: :boolean,
     adapter: :string,
     from_elixir_install: :boolean,
+    inside_docker_env: :boolean
   ]
 
   @impl true

installer/lib/phx_new/generator.ex

@@ -182,6 +182,17 @@ defmodule Phx.New.Generator do
     phoenix_path = phoenix_path(project, dev, false)
     phoenix_path_umbrella_root = phoenix_path(project, dev, true)
 
+    # detect if we're inside a docker env, but if we're in github actions,
+    # we want to treat it like regular env for end-user testing purposes
+    inside_docker_env? =
+      Keyword.get_lazy(opts, :inside_docker_env, fn ->
+        if System.get_env("GITHUB_ACTIONS") do
+          false
+        else
+          File.exists?("/.dockerenv")
+        end
+      end)
+
     # We lowercase the database name because according to the
     # SQL spec, they are case insensitive unless quoted, which
     # means creating a database like FoO is the same as foo in
@@ -243,7 +254,8 @@ defmodule Phx.New.Generator do
       dev: dev,
       from_elixir_install: from_elixir_install,
       elixir_install_otp_bin_path: from_elixir_install && elixir_install_otp_bin_path(),
-      elixir_install_bin_path: from_elixir_install && elixir_install_bin_path()
+      elixir_install_bin_path: from_elixir_install && elixir_install_bin_path(),
+      inside_docker_env?: inside_docker_env?
     ]
 
     %Project{project | binding: binding}

installer/templates/phx_single/config/dev.exs

@@ -6,10 +6,13 @@ import Config
 # The watchers configuration can be used to run external
 # watchers to your application. For example, we can use it
 # to bundle .js and .css sources.
-config :<%= @app_name %>, <%= @endpoint_module %>,
-  # Binding to loopback ipv4 address prevents access from other machines.
+config :<%= @app_name %>, <%= @endpoint_module %>,<%= if @inside_docker_env? do %>
+  # Bind to 0.0.0.0 to expose the server to the docker host machine.
+  # This makes make the service accessible from any network interface.
+  # Change to `ip: {127, 0, 0, 1}` to allow access only from the server machine.
+  http: [ip: {0, 0, 0, 0}, port: 4000],<% else %># Binding to loopback ipv4 address prevents access from other machines.
   # Change to `ip: {0, 0, 0, 0}` to allow access from other machines.
-  http: [ip: {127, 0, 0, 1}, port: 4000],
+  http: [ip: {127, 0, 0, 1}, port: 4000],<% end %>
   check_origin: false,
   code_reloader: true,
   debug_errors: true,

installer/templates/phx_umbrella/apps/app_name_web/config/dev.exs

@@ -6,10 +6,13 @@ import Config
 # The watchers configuration can be used to run external
 # watchers to your application. For example, we can use it
 # to bundle .js and .css sources.
-config :<%= @web_app_name %>, <%= @endpoint_module %>,
-  # Binding to loopback ipv4 address prevents access from other machines.
+config :<%= @web_app_name %>, <%= @endpoint_module %>,<%= if @inside_docker_env? do %>
+  # Bind to 0.0.0.0 to expose the server to the docker host machine.
+  # This makes make the service accessible from any network interface.
+  # Change to `ip: {127, 0, 0, 1}` to allow access only from the server machine.
+  http: [ip: {0, 0, 0, 0}, port: 4000],<% else %># Binding to loopback ipv4 address prevents access from other machines.
   # Change to `ip: {0, 0, 0, 0}` to allow access from other machines.
-  http: [ip: {127, 0, 0, 1}, port: 4000],
+  http: [ip: {127, 0, 0, 1}, port: 4000],<% end %>
   check_origin: false,
   code_reloader: true,
   debug_errors: true,

installer/test/phx_new_test.exs

@@ -149,6 +149,7 @@ defmodule Mix.Tasks.Phx.NewTest do
       assert_file("phx_blog/config/dev.exs", fn file ->
         assert file =~ "esbuild: {Esbuild,"
         assert file =~ "lib/phx_blog_web/(controllers|live|components)/.*(ex|heex)"
+        assert file =~ "http: [ip: {127, 0, 0, 1}, port: 4000]"
       end)
 
       # tailwind
@@ -829,4 +830,13 @@ defmodule Mix.Tasks.Phx.NewTest do
                "Creates a new Phoenix project."
     end)
   end
+
+  test "new from inside docker machine (simulated)" do
+    in_tmp("new without defaults", fn ->
+      Mix.Tasks.Phx.New.run([@app_name, "--inside-docker-env"])
+      assert_file("phx_blog/config/dev.exs", fn file ->
+        assert file =~ "http: [ip: {0, 0, 0, 0}, port: 4000]"
+      end)
+    end)
+  end
 end