railsの環境構築ができない

Question

Docker + wsl2でrails6の環境構築を行っております。コンテナにログインし、rails new を実行しようとすると謎のエラーにはまってしまいました、、、

Traceback (most recent call last):
        33: from /usr/local/bundle/bin/rails:23:in `<main>'
        32: from /usr/local/bundle/bin/rails:23:in `load'
        31: from /usr/local/bundle/gems/railties-6.0.3.1/exe/rails:10:in `<top (required)>'
        30: from /usr/local/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        29: from /usr/local/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in `require'
        28: from /usr/local/bundle/gems/railties-6.0.3.1/lib/rails/cli.rb:18:in `<top (required)>'
        27: from /usr/local/bundle/gems/railties-6.0.3.1/lib/rails/command.rb:46:in `invoke'
        26: from /usr/local/bundle/gems/railties-6.0.3.1/lib/rails/command/base.rb:69:in `perform'
        25: from /usr/local/bundle/gems/thor-1.0.1/lib/thor.rb:392:in `dispatch'
        24: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:127:in `invoke_command'
        23: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/command.rb:27:in `run'
        22: from /usr/local/bundle/gems/railties-6.0.3.1/lib/rails/commands/application/application_command.rb:26:in `perform'
        21: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/base.rb:485:in `start'
        20: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/group.rb:232:in `dispatch'
        19: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:134:in `invoke_all'
        18: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:134:in `map'
        17: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:134:in `each'
        16: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:134:in `block in invoke_all'
        15: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/invocation.rb:127:in `invoke_command'
        14: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/command.rb:27:in `run'
        13: from (eval):1:in `create_root'
        12: from /usr/local/bundle/gems/railties-6.0.3.1/lib/rails/generators/app_base.rb:161:in `create_root'
        11: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/actions/empty_directory.rb:14:in `empty_directory'
        10: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/actions.rb:93:in `action'
         9: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/actions/empty_directory.rb:50:in `invoke!'
         8: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/actions/empty_directory.rb:117:in `invoke_with_conflict_check'
         7: from /usr/local/bundle/gems/thor-1.0.1/lib/thor/actions/empty_directory.rb:52:in `block in invoke!'
         6: from /usr/local/lib/ruby/2.6.0/fileutils.rb:200:in `mkdir_p'
         5: from /usr/local/lib/ruby/2.6.0/fileutils.rb:200:in `each'
         4: from /usr/local/lib/ruby/2.6.0/fileutils.rb:215:in `block in mkdir_p'
         3: from /usr/local/lib/ruby/2.6.0/fileutils.rb:215:in `reverse_each'
         2: from /usr/local/lib/ruby/2.6.0/fileutils.rb:217:in `block (2 levels) in mkdir_p'
         1: from /usr/local/lib/ruby/2.6.0/fileutils.rb:239:in `fu_mkdir'
/usr/local/lib/ruby/2.6.0/fileutils.rb:239:in `mkdir': Permission denied @ dir_s_mkdir - /apps/myapp (Errno::EACCES)

Dokerfile

FROM oiax/rails6-deps:latest

ARG UID=1000
ARG GID=1000

RUN mkdir /var/mail
RUN groupadd -g $GID devel
RUN useradd -u $UID -g devel -m devel
RUN echo "devel ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers

WORKDIR /tmp
COPY init/Gemfile /tmp/Gemfile
COPY init/Gemfile.lock /tmp/Gemfile.lock
RUN bundle install

COPY ./apps /apps

RUN apk add --no-cache openssl

USER devel

RUN openssl rand -hex 64 > /home/devel/.secret_key_base
RUN echo $'export SECRET_KEY_BASE=$(cat /home/devel/.secret_key_base)' \
  >> /home/devel/.bashrc

WORKDIR /apps

Gemfile

source 'https://rubygems.org'
gem 'rails', '~> 6.0.3.1'

.gitignore

/apps/*
!/apps/.keep
/tmp/*
!/tmp/.keep
docker-compose.override.yml

試したこと

ruby, railsのバージョンを確認
local のRubyの確認

Answer 1

エラーとは、こちらですね。

/usr/local/lib/ruby/2.6.0/fileutils.rb:239:in `mkdir': Permission denied @ dir_s_mkdir - /apps/myapp (Errno::EACCES)

これは、コンテナ内の「/apps/myapp」ディレクトリを作成しようとしても、権限が無いので拒否（Permission denied）されています。

Dockerfile では、USER devel の指定がありました。

つまり、このユーザ devel で mkdir /app/myapp しようとして、権限が無い状態です。

コンテナ実行時に、権限の設定（例： RUN chown -R devel:devel /myapp ）を入れておけば回避できるでしょう。