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 

Solution 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.

Solution 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.

Comments

[Chase Gibbons]

You saved my life man!! Why does this work exactly? Are there random one off volumes that get created that I don't know about or something, which were holding onto some other variation of the "postgres" host address? I tried deleting my named volumes one-by-one numerous times to no avail previously, but this did the trick for me!!! Thank you very much good sir.

[Joshua Hunter]

I'm not sure, what causes it, honestly. I was glad to finally find something that worked, though.