Nginx rendering 502 error page - ruby-on-rails

Question

I'm trying to configure nginx with puma to server my Ruby on Rails application. Whenever I visit my page I get a 502 bad gateway error.
/etc/nginx/sites-enabled/puma-api
upstream puma_puma-api_production {
server unix:/home/deploy/apps/puma-api/shared/tmp/sockets/puma-api-puma.sock fail_timeout=0;
}
server {
listen 80 default;
client_max_body_size 4G;
keepalive_timeout 10;
error_page 500 502 504 /500.html;
error_page 503 #503;
root /home/deploy/apps/puma-api/current/public;
try_files $uri/index.html $uri #puma_puma-api_production;
location #puma_puma-api_production {
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_pass http://puma_puma-api_production;
# limit_req zone=one;
access_log /home/deploy/apps/puma-api/shared/log/nginx.access.log;
error_log /home/deploy/apps/puma-api/shared/log/nginx.error.log;
}
location ^~ /assets/ {
gzip_static on;
expires max;
add_header Cache-Control public;
}
location = /50x.html {
root html;
}
location = /404.html {
root html;
}
location #503 {
error_page 405 = /system/maintenance.html;
if (-f $document_root/system/maintenance.html) {
rewrite ^(.*)$ /system/maintenance.html break;
}
rewrite ^(.*)$ /503.html break;
}
if ($request_method !~ ^(GET|HEAD|PUT|PATCH|POST|DELETE|OPTIONS)$ ){
return 405;
}
if (-f $document_root/system/maintenance.html) {
return 503;
}
location ~ \.(php|html)$ {
return 405;
}
}
/etc/nginx/nginx.conf
user nginx;
worker_processes 1;
error_log /var/log/nginx/error.log;
pid /var/run/nginx.pid;
events {
worker_connections 1024;
}
http {
include /etc/nginx/mime.types;
default_type application/octet-stream;
access_log /var/log/nginx/access.log;
sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_requests 100;
keepalive_timeout 65;
gzip on;
gzip_http_version 1.0;
gzip_comp_level 2;
gzip_proxied any;
gzip_vary off;
gzip_types text/plain text/css application/x-javascript text/xml application/xml application/rss+xml application/atom+xml text/javascript application/javascript application/json text/mathml;
gzip_min_length 1000;
gzip_disable "MSIE [1-6]\.";
variables_hash_max_size 1024;
variables_hash_bucket_size 64;
server_names_hash_bucket_size 64;
types_hash_max_size 2048;
types_hash_bucket_size 64;
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}
app/config/puma.rb
workers Integer(ENV['WEB_CONCURRENCY'] || 2)
threads_count = Integer(ENV['MAX_THREADS'] || 5)
threads threads_count, threads_count
preload_app!
rackup DefaultRackup
port ENV['PORT'] || 5000
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
deploy.rb
# config valid only for current version of Capistrano
lock '3.4.0'
set :application, 'puma-api'
set :repo_url, 'git#github.com:chaione/puma-api.git'
set :user, 'deploy'
# set :nginx_domains, 'localhost'
# set :app_server_socket, "#{shared_path}/sockets/puma-#{fetch :application}.sock"
# Default branch is :master
ask :branch, `git rev-parse --abbrev-ref HEAD`.chomp
# Default deploy_to directory is /var/www/my_app_name
# set :deploy_to, '/var/www/my_app_name'
set :puma_threads, [4, 16]
set :puma_workers, 0
# Don't change these unless you know what you're doing
set :pty, true
set :use_sudo, false
set :stage, :production
set :deploy_via, :remote_cache
set :deploy_to, "/home/#{fetch(:user)}/apps/#{fetch(:application)}"
set :puma_bind, "unix://#{shared_path}/tmp/sockets/#{fetch(:application)}-puma.sock"
set :puma_state, "#{shared_path}/tmp/pids/puma.state"
set :puma_pid, "#{shared_path}/tmp/pids/puma.pid"
set :puma_access_log, "#{release_path}/log/puma.error.log"
set :puma_error_log, "#{release_path}/log/puma.access.log"
set :ssh_options, forward_agent: true, user: fetch(:user), keys: %w(~/.ssh/id_rsa.pub)
set :puma_preload_app, true
set :puma_worker_timeout, nil
set :puma_init_active_record, true
namespace :puma do
desc 'Create Directories for Puma Pids and Socket'
task :make_dirs do
on roles(:app) do
execute "mkdir #{shared_path}/tmp/sockets -p"
execute "mkdir #{shared_path}/tmp/pids -p"
end
end
before :start, :make_dirs
end
namespace :deploy do
desc 'Make sure local git is in sync with remote.'
task :check_revision do
on roles(:app) do
unless `git rev-parse HEAD` == `git rev-parse origin/master`
puts 'WARNING: HEAD is not the same as origin/master'
puts 'Run `git push` to sync changes.'
exit
end
end
end
desc 'Initial Deploy'
task :initial do
on roles(:app) do
before 'deploy:restart', 'puma:start'
invoke 'deploy'
end
end
desc 'Restart application'
task :restart do
on roles(:app), in: :sequence, wait: 5 do
invoke 'puma:restart'
end
end
# before :starting, :check_revision
after :finishing, :compile_assets
after :finishing, :cleanup
after :finishing, :restart
end
# # Default value for :linked_files is []
# set :linked_dirs, fetch(:linked_dirs, []).push('log', 'tmp/pids', 'tmp/cache', 'tmp/sockets', 'vendor/bundle', 'public/system', 'public/images')
# set :linked_files, fetch(:linked_files, []).push('config/database.yml', 'config/secrets.yml')
# Default value for default_env is {}
# set :default_env, { path: "/opt/ruby/bin:$PATH" }
namespace :deploy do
after :restart, :clear_cache do
on roles(:web), in: :groups, limit: 3, wait: 10 do
# Here we can do anything such as:
# within release_path do
# execute :rake, 'cache:clear'
# end
end
end
end
app recipe
# create www directory
directory '/var/www' do
user node['user']['name']
group node['group']
mode 0755
end
# create shared directory structure for app
path = "/var/www/#{node['app']}/shared/config"
execute "mkdir -p #{path}" do
user node['user']['name']
group node['group']
creates path
end
# create database.yml file
template "#{path}/database.yml" do
source 'database.yml.erb'
mode 0640
owner node['user']['name']
group node['group']
end

Answer 1

You have nginx communicating with your puma server via socket
/home/deploy/apps/puma-api/shared/tmp/sockets/puma-api-puma.sock
You have puma creating this socket at
set :puma_bind, "unix://#{shared_path}/tmp/sockets/#{fetch(:application)}-puma.sock"
I can't see shared_path defined anywhere in your code though. Make sure that these two match (or just hardcode the path to eliminate variables for now).
I would also first check if /home/deploy/apps/puma-api/shared/tmp/sockets/puma-api-puma.sock even exists.