Elixir Phoenix shutdown: failed to start child

Question

I'm getting the following error when starting my app in production mode. All works fine on dev side, can migrate, compile and release without issue on the production app but when running it, it crashes on start. I'm sure it is something very obvious I am missing. I am running Erlang 19 and Elixir 1.3.2.

17:42:52.768 [info] Application curriculum exited: Curriculum.start(:normal, []) returned an error: shutdown: failed to start child: Curriculum.Endpoint ** (EXIT) shutdown: failed to start child: Phoenix.Endpoint.Server ** (EXIT) an exception was raised: ** (FunctionClauseError) no function clause matching in System.get_env/1 (elixir) lib/system.ex:358: System.get_env(4000) (phoenix) lib/phoenix/endpoint/server.ex:34: Phoenix.Endpoint.Server.to_port/1 (phoenix) lib/phoenix/endpoint/server.ex:28: Phoenix.Endpoint.Server.default/3 (phoenix) lib/phoenix/endpoint/server.ex:17: anonymous fn/5 in Phoenix.Endpoint.Server.init/1 (elixir) lib/enum.ex:1623: Enum."-reduce/3-lists^foldl/2-0-"/3 (phoenix) lib/phoenix/endpoint/server.ex:15: Phoenix.Endpoint.Server.init/1 (stdlib) supervisor.erl:294: :supervisor.init/1 (stdlib) gen_server.erl:328: :gen_server.init_it/6 {"Kernel pid terminated",application_controller,"{application_start_failure,curriculum,{{shutdown,{failed_to_start_child,'Elixir.Curriculum.Endpoint',{shutdown,{failed_to_start_child,'Elixir.Phoenix.Endpoint.Server',{function_clause,[{'Elixir.System',get_env,[4000],[{file,\"lib/system.ex\"},{line,358}]},{'Elixir.Phoenix.Endpoint.Server',to_port,1,[{file,\"lib/phoenix/endpoint/server.ex\"},{line,34}]},{'Elixir.Phoenix.Endpoint.Server',default,3,[{file,\"lib/phoenix/endpoint/server.ex\"},{line,28}]},{'Elixir.Phoenix.Endpoint.Server','-init/1-fun-0-',5,[{file,\"lib/phoenix/endpoint/server.ex\"},{line,17}]},{'Elixir.Enum','-reduce/3-lists^foldl/2-0-',3,[{file,\"lib/enum.ex\"},{line,1623}]},{'Elixir.Phoenix.Endpoint.Server',init,1,[{file,\"lib/phoenix/endpoint/server.ex\"},{line,15}]},{supervisor,init,1,[{file,\"supervisor.erl\"},{line,294}]},{gen_server,init_it,6,[{file,\"gen_server.erl\"},{line,328}]}]}}}}},{'Elixir.Curriculum',start,[normal,[]]}}}"}

Prod.exs file contents

http: [port: {:system, 4000}],url: [host: "example.com"],cache_static_manifest: "priv/static/manifest.json",server: true
config :phoenix, :serve_endpoints, true

import_config "prod.secret.exs"

Answer 1

Your value for port in config/prod.exs is wrong. It should either be:

port: 4000

to always run on port 4000, or:

port: {:system, "PORT"}

to read the port from the environment variable PORT (you can change the name to any other string).