I have a Ruby on Rails application deployed in DigitalOcean ubuntu image.

My versions are:

ruby 2.6.0
rails 5.1.5.rc1
puma 4.3.6

I deploy my application using Capistrano

deploy.rb

# config valid for current version and patch releases of Capistrano
lock "~> 3.14.1"

set :application, "ricsonwin"
set :repo_url, "git@github.com:XXX/XXX.git"
set :deploy_user, "deploy"

set :pty, true
set :linked_files, %w{config/database.yml config/secrets.yml}
set :linked_dirs, %w{log tmp/pids tmp/cache tmp/sockets vendor/bundle public/system public/uploads}

set :keep_releases, 5
set :rvm_ruby_version, '2.6.0' # Edit this depends on the rvm ruby version installed in the server
set :bundle_binstubs, nil

set :puma_role, :app
set :puma_threads, [0, 8]
set :puma_workers, 0
set :puma_worker_timeout, nil
set :puma_init_active_record, true
set :puma_preload_app, false

# Creates database
before 'deploy:migrate', 'deploy:db:create'

after 'deploy:symlink:release', 'puma:config'

namespace :puma do
  Rake::Task[:restart].clear_actions

  desc "Overwritten puma:restart task"
  task :restart do
    puts "Overwriting puma:restart to ensure that puma is running. Effectively, we are just starting Puma."
    puts "A solution to this should be found."
    invoke 'puma:stop'
    invoke 'puma:start'
  end
end

deploy/production.log

server 'XXX.XXX.XXX.XXX', user: 'deploy', roles: %w{web app db}, primary: true

set :location, 'XXX.XXX.XXX.XXX'
role :db, fetch(:location), primary: true
set :branch, :master

set :full_app_name, "#{fetch(:application)}_#{fetch(:stage)}"
set :deploy_to, "/srv/www/apps/#{fetch(:full_app_name)}"

set :stage, :production
set :rails_env, :production
set :console_env, :production
set :environment, :production

set :rvm_type, :user

set :puma_env, fetch(:rack_env, fetch(:rails_env, 'production'))
set :puma_rackup, -> { File.join(current_path, 'config.ru') }
set :puma_state, "#{shared_path}/tmp/pids/puma.state"
set :puma_pid, "#{shared_path}/tmp/pids/puma.pid"
set :puma_bind, ["tcp://0.0.0.0:9292"]
set :puma_conf, "#{shared_path}/puma.rb"
set :puma_access_log, "#{shared_path}/log/puma_error.log"
set :puma_error_log, "#{shared_path}/log/puma_access.log"

config/puma.rb

if Rails.env.production?

  directory = "/srv/www/apps/myapp_production/current"
  rackup "/srv/www/apps/myapp_production/current/config.ru"
  environment Rails.env

  pidfile "/srv/www/apps/myapp_production/shared/tmp/pids/puma.pid"
  state_path "/srv/www/apps/myapp_production/shared/tmp/pids/puma.state"
  stdout_redirect "/srv/www/apps/myapp_production/shared/log/puma_access.log", "/srv/www/apps/myapp_production/shared/log/puma_error.log", true

  threads 4, 16
  workers 1

  bind "unix:///srv/www/apps/myapp_production/shared/tmp/sockets/puma.sock"

  preload_app!

  on_worker_boot do
    ActiveSupport.on_load(:active_record) do
    ActiveRecord::Base.establish_connection
    end
  end

else
  workers Integer(ENV['WEB_CONCURRENCY'] || 2)
  threads_count = Integer(ENV['RAILS_MAX_THREADS'] || 5)
  threads threads_count, threads_count

  preload_app!

  rackup      DefaultRackup
  port        ENV['PORT']     || 3000
  environment ENV['RACK_ENV'] || 'development'

  on_worker_boot do
    # Worker specific setup for Rails 4.1+
    # See: https://devcenter.heroku.com/articles/deploying-rails-applications-with-the-puma-web-server#on-worker-boot
    ActiveRecord::Base.establish_connection
  end
end

When I check the logs
production.log

Item Load (0.3ms)  SELECT  "items".* FROM "items" WHERE "items"."id" = $1 LIMIT $2  [["id", 208], ["LIMIT", 1]]
  CACHE Unit Load (0.0ms)  SELECT  "units".* FROM "units" WHERE "units"."id" = $1 LIMIT $2  [["id", 4], ["LIMIT", 1]]
  Item Load (0.3ms)  SELECT  "items".* FROM "items" WHERE "items"."id" = $1 LIMIT $2  [["id", 215], ["LIMIT", 1]]
  CACHE Unit Load (0.0ms)  SELECT  "units".* FROM "units" WHERE "units"."id" = $1 LIMIT $2  [["id", 4], ["LIMIT", 1]]
  Item Load (0.2ms)  SELECT  "items".* FROM "items" WHERE "items"."id" = $1 LIMIT $2  [["id", 198], ["LIMIT", 1]]
  CACHE Unit Load (0.0ms)  SELECT  "units".* FROM "units" WHERE "units"."id" = $1 LIMIT $2  [["id", 10], ["LIMIT", 1]]
  Rendering text template
  Rendered text template (0.0ms)
Sent data Delivery Receipt 12-2020-001.pdf (0.5ms)
Completed 200 OK in 4326ms (Views: 0.3ms | ActiveRecord: 37.4ms)

puma_access.log

=== puma startup: 2020-12-01 01:07:13 +0000 ===

puma_error.log

Puma starting in single mode...
* Version 4.3.1 (ruby 2.6.0-p0), codename: Mysterious Traveller
* Min threads: 0, max threads: 8
* Environment: production
* Daemonizing...
=== puma startup: 2020-09-21 05:16:28 +0000 ===
=== puma startup: 2020-09-21 05:17:39 +0000 ===
* Listening on tcp://0.0.0.0:9292
=== puma startup: 2020-09-21 06:11:35 +0000 ===
- Gracefully stopping, waiting for requests to finish
=== puma shutdown: 2020-09-21 06:11:35 +0000 ===

My application is running but after a while it will stop, I’m not sure what’s causing the error.