Rails could not translate host name "postgres" to address: Name or service not known (PG::ConnectionBad)

Question

I'm working on a Rails 4.2.3 project with ruby 2.2.2 (Running ubuntu 16.04). It was working ok but after revisiting it after a while I can't serve. I've tried searching but all situations don't seem to be of help. Here's the error log:

bigzoo@bigzoo:~/Documents/projects/proj$ rs
=> Booting Puma
=> Rails 4.2.3 application starting in development on http://localhost:3000
=> Run `rails server -h` for more startup options
=> Ctrl-C to shutdown server
Exiting
/home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `initialize': could not translate host name "postgres" to address: Name or service not known (PG::ConnectionBad)
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `new'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:655:in `connect'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:242:in `initialize'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `new'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/postgresql_adapter.rb:44:in `postgresql_connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:438:in `new_connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:448:in `checkout_new_connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:422:in `acquire_connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:349:in `block in checkout'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:348:in `checkout'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:263:in `block in connection'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/monitor.rb:211:in `mon_synchronize'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:262:in `connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_adapters/abstract/connection_pool.rb:571:in `retrieve_connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_handling.rb:113:in `retrieve_connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/connection_handling.rb:87:in `connection'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/querying.rb:39:in `find_by_sql'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/relation.rb:638:in `exec_queries'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/relation.rb:514:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/relation.rb:243:in `to_a'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activerecord-4.2.3/lib/active_record/relation/delegation.rb:46:in `map'
    from /home/bigzoo/Documents/projects/proj/app/admin/product.rb:62:in `block in <top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/dsl.rb:15:in `instance_exec'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/dsl.rb:15:in `run_registration_block'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/namespace.rb:223:in `parse_registration_block'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/namespace.rb:48:in `register'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:154:in `register'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin.rb:75:in `register'
    from /home/bigzoo/Documents/projects/proj/app/admin/product.rb:1:in `<top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:268:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:268:in `block in load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:268:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:212:in `block in load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/error.rb:41:in `capture'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:212:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:204:in `block in load!'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:204:in `each'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:204:in `load!'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin/application.rb:226:in `routes'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/bundler/gems/activeadmin-21f76b1faf65/lib/active_admin.rb:79:in `routes'
    from /home/bigzoo/Documents/projects/proj/config/routes.rb:20:in `block in <top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/actionpack-4.2.3/lib/action_dispatch/routing/route_set.rb:434:in `instance_exec'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/actionpack-4.2.3/lib/action_dispatch/routing/route_set.rb:434:in `eval_block'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/actionpack-4.2.3/lib/action_dispatch/routing/route_set.rb:412:in `draw'
    from /home/bigzoo/Documents/projects/proj/config/routes.rb:1:in `<top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:268:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:268:in `block in load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:268:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:40:in `block in load_paths'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:40:in `each'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:40:in `load_paths'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:16:in `reload!'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:26:in `block in updater'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/file_update_checker.rb:75:in `call'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/file_update_checker.rb:75:in `execute'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:27:in `updater'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/routes_reloader.rb:7:in `execute_if_updated'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application/finisher.rb:69:in `block in <module:Finisher>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/initializable.rb:30:in `instance_exec'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/initializable.rb:30:in `run'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/initializable.rb:55:in `block in run_initializers'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:226:in `block in tsort_each'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:348:in `block (2 levels) in each_strongly_connected_component'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:429:in `each_strongly_connected_component_from'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:347:in `block in each_strongly_connected_component'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `each'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `call'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:345:in `each_strongly_connected_component'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:224:in `tsort_each'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/tsort.rb:203:in `tsort_each'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/initializable.rb:54:in `run_initializers'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/application.rb:352:in `initialize!'
    from /home/bigzoo/Documents/projects/proj/config/environment.rb:5:in `<top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:274:in `require'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:274:in `block in require'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:240:in `load_dependency'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/activesupport-4.2.3/lib/active_support/dependencies.rb:274:in `require'
    from /home/bigzoo/Documents/projects/proj/config.ru:3:in `block in <main>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/builder.rb:55:in `instance_eval'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/builder.rb:55:in `initialize'
    from /home/bigzoo/Documents/projects/proj/config.ru:in `new'
    from /home/bigzoo/Documents/projects/proj/config.ru:in `<main>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/builder.rb:49:in `eval'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/builder.rb:49:in `new_from_string'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/builder.rb:40:in `parse_file'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/server.rb:299:in `build_app_and_options_from_config'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/server.rb:208:in `app'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/server.rb:61:in `app'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/rack-1.6.5/lib/rack/server.rb:336:in `wrapped_app'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/server.rb:139:in `log_to_stdout'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/server.rb:78:in `start'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:80:in `block in server'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:75:in `tap'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:75:in `server'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/railties-4.2.3/lib/rails/commands.rb:17:in `<top (required)>'
    from /home/bigzoo/Documents/projects/proj/bin/rails:8:in `require'
    from /home/bigzoo/Documents/projects/proj/bin/rails:8:in `<top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/lib/spring/client/rails.rb:28:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/lib/spring/client/rails.rb:28:in `call'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/lib/spring/client/command.rb:7:in `call'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/lib/spring/client.rb:26:in `run'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/bin/spring:48:in `<top (required)>'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/lib/spring/binstub.rb:11:in `load'
    from /home/bigzoo/Documents/projects/proj/.bundle/ruby/2.2.0/gems/spring-1.3.6/lib/spring/binstub.rb:11:in `<top (required)>'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from /home/bigzoo/.rbenv/versions/2.2.2/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
    from /home/bigzoo/Documents/projects/proj/bin/spring:13:in `<top (required)>'
    from bin/rails:3:in `load'
    from bin/rails:3:in `<main>'

The only issue seems to be connecting to postgres.

PS. I've already tried running unset DATABASE_URL if anyone is feeling compelled to suggest that.

Extra info:

bigzoo@bigzoo:~/Documents/projects/proj$ sudo netstat -atpn | grep 5432
[sudo] password for bigzoo: 
tcp        0      0 127.0.0.1:5432          0.0.0.0:*               LISTEN      1744/postgres 

Answer 1

Adding the line below to /etc/hosts did the trick.

127.0.0.1 postgres

did the trick.

Rails uses the host name postgres and leaves it up to the system to direct postgres to the host and port as required. The line above allows the mapping to take place if it doesn't work for some reason.

Credits @mudasobwa.

PS. To edit /etc/hosts just type (in your console)

sudo nano /etc/hosts

To open it and add the line.

Answer 2

This happened to me on a container that I had been using regularly. It just randomly started throwing this error and not resolving.

I eventually solved it with

docker system prune --volumes

running it without the volumes flag didn't resolve it.