add sample apps under some supervisor tools

unicorn+daemontools/Dockerfile

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+FROM ruby:2.7.4
+
+RUN apt-get update -qq && apt-get install wget && apt-get install psmisc
+
+WORKDIR /sample
+COPY ["./src/Gemfile", "./"]
+
+RUN gem install bundler --version 1.17.2
+
+# See: http://cr.yp.to/daemontools/install.html
+# See: http://cr.yp.to/daemontools/start.html
+# See: http://thedjbway.b0llix.net/daemontools/installation.html
+RUN mkdir -p /package && chmod 1755 /package && cd /package && \
+    wget http://cr.yp.to/daemontools/daemontools-0.76.tar.gz && gunzip daemontools-0.76.tar && tar -xpf daemontools-0.76.tar && rm -f daemontools-0.76.tar && \
+    cd admin/daemontools-0.76 && \
+    wget http://thedjbway.b0llix.net/patches/daemontools-0.76.sigq12.patch && patch -t -p1 < ./daemontools-0.76.sigq12.patch && \
+    wget http://qmail.org/moni.csi.hu/pub/glibc-2.3.1/daemontools-0.76.errno.patch && patch -t -p1 < ./daemontools-0.76.errno.patch && \
+    package/install && \
+    mkdir -p /service && chmod 755 /service
+
+COPY ["./run", "/service/sample_server/run"]
+
+RUN mkdir -p /service/sample_server/log && echo "#!/bin/sh\\nexec multilog t ./main" >> /service/sample_server/log/run && chmod 755 /service/sample_server/log/run && \
+    chmod +t /service/sample_server
+
+COPY . /sample

unicorn+daemontools/README.md

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+# Playground: Unicorn Graceful Restart under daemontools
+
+```sh
+docker image build --file ./Dockerfile --tag sample_unicorn_daemontools:t01 --rm .
+docker container run -it --rm sample_unicorn_daemontools:t01 /bin/bash
+```
+
+```bash
+/command/svscanboot &
+
+pstree --show-pids
+ps -f -o user,pid,ppid,start,command --forest
+
+svstat /service/sample_server/
+
+curl localhost:8080 -w "\n"
+
+# Graceful Restart
+svc -2 /service/sample_server # SIGUSR2 + QUIT to old master. See unicorn.conf.rb
+pstree --show-pids
+ps -f -o user,pid,ppid,start,command --forest
+
+svstat /service/sample_server/
+svstat /service/sample_server/
+svstat /service/sample_server/ # => pid が毎回変わってることが確認できる
+
+cat unicorn_stderr.log # => エラーで永遠に失敗してるのがわかる
+
+tai64nlocal < /service/sample_server/log/main/current
+```

unicorn+daemontools/run

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+#!/bin/sh
+
+exec 2>&1 \
+sh -c '
+  cd /sample
+  bundle install
+  exec bundle exec unicorn ./src/config.ru --config-file ./src/unicorn.conf_with_fork_hook.rb
+'
+

unicorn+daemontools/src/Gemfile

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+source 'https://rubygems.org'
+
+gem 'unicorn', '~> 6.0'
+gem 'rack', '~> 2.2', '>= 2.2.3'

unicorn+daemontools/src/config.ru

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+# coding: utf-8
+
+require_relative 'sample.rb'
+run Sample.new

unicorn+daemontools/src/sample.rb

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+class Sample
+  def call(env)
+     [
+      200,
+      { 'Content-Type' => 'text/html' },
+      ['ok'],
+    ]
+  end
+end

unicorn+daemontools/src/unicorn.conf_with_fork_hook.rb

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+# See: https://github.com/defunkt/unicorn/blob/master/examples/unicorn.conf.minimal.rb
+# See: https://github.com/defunkt/unicorn/blob/master/examples/unicorn.conf.rb
+
+worker_processes 2
+
+stderr_path './unicorn_stderr.log'
+stdout_path './unicorn_stdout.log'
+
+pid 'unicorn.pid'
+
+listen 8080, :tcp_nopush => true
+
+# See: https://github.com/defunkt/unicorn/blob/93e154e16b87f943a20fa720e002c67c9d17c30b/examples/unicorn.conf.rb#L71
+before_fork do |server, worker|
+  # The following is only recommended for memory/DB-constrained
+  # installations.  It is not needed if your system can house
+  # twice as many worker_processes as you have configured.
+
+  # This allows a new master process to incrementally
+  # phase out the old master process with SIGTTOU to avoid a
+  # thundering herd (especially in the "preload_app false" case)
+  # when doing a transparent upgrade.  The last worker spawned
+  # will then kill off the old master process with a SIGQUIT.
+  old_pid = "#{server.config[:pid]}.oldbin"
+  if old_pid != server.pid
+    begin
+      sig = (worker.nr + 1) >= server.worker_processes ? :QUIT : :TTOU
+      Process.kill(sig, File.read(old_pid).to_i)
+    rescue Errno::ENOENT, Errno::ESRCH
+    end
+  end
+
+  # Throttle the master from forking too quickly by sleeping.  Due
+  # to the implementation of standard Unix signal handlers, this
+  # helps (but does not completely) prevent identical, repeated signals
+  # from being lost when the receiving process is busy.
+  sleep 1
+end

unicorn+server-starter+daemontools/Dockerfile

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+FROM ruby:2.6.2
+
+WORKDIR /sample
+
+RUN apt-get update -qq && apt-get install -y wget psmisc gcc perlbrew
+
+# See: http://cr.yp.to/daemontools/install.html
+# See: http://cr.yp.to/daemontools/start.html
+# See: http://thedjbway.b0llix.net/daemontools/installation.html
+RUN mkdir -p /package && chmod 1755 /package && cd /package && \
+    wget http://cr.yp.to/daemontools/daemontools-0.76.tar.gz && gunzip daemontools-0.76.tar && tar -xpf daemontools-0.76.tar && rm -f daemontools-0.76.tar && \
+    cd admin/daemontools-0.76 && \
+    wget http://thedjbway.b0llix.net/patches/daemontools-0.76.sigq12.patch && patch -t -p1 < ./daemontools-0.76.sigq12.patch && \
+    wget http://qmail.org/moni.csi.hu/pub/glibc-2.3.1/daemontools-0.76.errno.patch && patch -t -p1 < ./daemontools-0.76.errno.patch && \
+    package/install && \
+    mkdir -p /service && chmod 755 /service
+
+RUN mkdir -p /service/sample_server/log && echo "#!/bin/sh\\nexec multilog t ./main" >> /service/sample_server/log/run && chmod 755 /service/sample_server/log/run && \
+    chmod +t /service/sample_server
+
+ENV PERLBREW_ROOT=/perl5
+RUN perlbrew available && perlbrew init && \
+    echo ". ${PERLBREW_ROOT}/etc/bashrc" >> ~/.bashrc && \
+    mkdir -p ${PERLBREW_ROOT}/perl-5.16.1 && mkdir -p ${PERLBREW_ROOT}/dists && mkdir -p ${PERLBREW_ROOT}/build/perl-5.16.1 && \
+    perlbrew install perl-5.16.1 --notest && \
+    echo ". ${PERLBREW_ROOT}/perls/perl-5.16.1/bin" >> /.bashrc && \
+    echo ". ${PERLBREW_ROOT}/bin" >> /.bashrc && \
+    perlbrew switch perl-5.16.1 && \
+    perlbrew install-cpanm && \
+    /perl5/bin/cpanm KAZUHO/Server-Starter-0.35.tar.gz --notest
+
+COPY ["./src/Gemfile", "./"]
+COPY ["./src/Gemfile.lock", "./"]
+RUN gem install bundler --version 1.17.3 && bundle install
+
+COPY ["./run", "/service/sample_server/run"]
+
+COPY . /sample