Does anyone know why I’m getting these tcp_closed errors or if I can ignore them? The errors are logged less frequently if I set the pool_size to 1 instead of 10. Otherwise, the tcp_closed errors are logged multiple times per minute forever.

It’s just a new Phoenix app with the Repo configured to a SQL Server on Azure SQL. It’s running in a Docker container on Azure Web App or Web Service for Linux.

ELIXIR_VERSION=1.14.5
OTP_VERSION=25.3.2.5
DEBIAN_VERSION=bullseye-20230612-slim

  config :app_name, AppName.Repo,
    username: "username",
    password: "password",
    hostname: "hostname.database.windows.net",
    database: "PhoenixDemo",
    ssl: :required,
    ssl_opts: [
      cacerts: :public_key.cacerts_get(),
      customize_hostname_check: [
        # match_fun: :public_key.pkix_verify_hostname_match_fun(:https)
        # match_fun: fn arg1, arg2 ->
        #   dbg
        #   true
        # end
        match_fun: fn _, _ -> true end
      ],
      # verify_fun: {&:ssl_verify_hostname.verify_fun/3, []},
      verify: :verify_peer
    ],
    stacktrace: true,
    show_sensitive_data_on_connection_error: true,
    pool_size: 10

2023-08-27T11:00:31.165568384Z 11:00:31.165 [error] GenServer #PID<0.7281.0> terminating
2023-08-27T11:00:31.165607985Z ** (stop) :tcp_closed
2023-08-27T11:00:31.165614385Z Last message: {:tcp_closed, #Port<0.1783>}

2023-08-27T11:00:44.382799422Z 11:00:44.382 [error] GenServer #PID<0.7294.0> terminating
2023-08-27T11:00:44.382851424Z ** (stop) :tcp_closed
2023-08-27T11:00:44.382857724Z Last message: {:tcp_closed, #Port<0.1787>}

2023-08-27T11:00:50.868232946Z 11:00:50.867 [error] GenServer #PID<0.7306.0> terminating
2023-08-27T11:00:50.868293847Z ** (stop) :tcp_closed
2023-08-27T11:00:50.868302347Z Last message: {:tcp_closed, #Port<0.1791>}

2023-08-27T11:00:55.510507526Z 11:00:55.509 [error] GenServer #PID<0.7318.0> terminating
2023-08-27T11:00:55.510555327Z ** (stop) :tcp_closed
2023-08-27T11:00:55.510560527Z Last message: {:tcp_closed, #Port<0.1795>}

I get this if I :sys.trace

2023-08-28T04:42:49.047272402Z: [INFO]  ** (stop) :tcp_closed
2023-08-28T04:42:49.047283902Z: [INFO]  Last message: {:tcp_closed, #Port<0.34294>}
2023-08-28T04:42:49.053868256Z: [INFO]  *DBG* <0.282.3> got {'EXIT',<0.283.3>,
2023-08-28T04:42:49.053900657Z: [INFO]                          {{badmatch,nil},
2023-08-28T04:42:49.053906857Z: [INFO]                           [{'Elixir.Tds.Tls','assert_connected!',1,
2023-08-28T04:42:49.053911557Z: [INFO]                                [{file,"lib/tds/tls.ex"},{line,86}]},
2023-08-28T04:42:49.053916558Z: [INFO]                            {'Elixir.Tds.Tls',send,2,
2023-08-28T04:42:49.053921158Z: [INFO]                                [{file,"lib/tds/tls.ex"},{line,41}]},
2023-08-28T04:42:49.053925458Z: [INFO]                            {tls_sender,send_tls_alert,2,
2023-08-28T04:42:49.053929858Z: [INFO]                                [{file,"tls_sender.erl"},{line,489}]},
2023-08-28T04:42:49.053934358Z: [INFO]                            {tls_sender,connection,3,
2023-08-28T04:42:49.053938858Z: [INFO]                                [{file,"tls_sender.erl"},{line,277}]},
2023-08-28T04:42:49.053959159Z: [INFO]                            {gen_statem,loop_state_callback,11,
2023-08-28T04:42:49.053963759Z: [INFO]                                [{file,"gen_statem.erl"},{line,1426}]},
2023-08-28T04:42:49.053968459Z: [INFO]                            {proc_lib,init_p_do_apply,3,
2023-08-28T04:42:49.053973059Z: [INFO]                                [{file,"proc_lib.erl"},{line,240}]}]}}
2023-08-28T04:42:49.053977759Z: [INFO]  *DBG* <0.282.3> new state {state,
2023-08-28T04:42:49.053981959Z: [INFO]                             {<0.282.3>,tls_dyn_connection_sup},
2023-08-28T04:42:49.053986259Z: [INFO]                             one_for_all,
2023-08-28T04:42:49.053990459Z: [INFO]                             {[receiver],
2023-08-28T04:42:49.053994659Z: [INFO]                              #{receiver =>
2023-08-28T04:42:49.053998859Z: [INFO]                                 {child,<0.284.3>,receiver,
2023-08-28T04:42:49.054003560Z: [INFO]                                  {ssl_gen_statem,start_link,undefined},
2023-08-28T04:42:49.054008560Z: [INFO]                                  temporary,true,5000,worker,
2023-08-28T04:42:49.054013260Z: [INFO]                                  [ssl_gen_statem,tls_connection,
2023-08-28T04:42:49.054017960Z: [INFO]                                   tls_connection_1_3]}}},
2023-08-28T04:42:49.054023060Z: [INFO]                             undefined,0,3600,[],0,any_significant,
2023-08-28T04:42:49.054027860Z: [INFO]                             tls_dyn_connection_sup,[]}
2023-08-28T04:42:49.054032760Z: [INFO]  *DBG* <0.282.3> got {'EXIT',<0.284.3>,{shutdown,normal}}
2023-08-28T04:42:50.308597299Z: [INFO]  04:42:50.308 [error] GenServer #PID<0.264.3> terminating
2023-08-28T04:42:50.308645800Z: [INFO]  ** (stop) :tcp_closed
2023-08-28T04:42:50.308653600Z: [INFO]  Last message: {:tcp_closed, #Port<0.34293>}
2023-08-28T04:42:50.315401459Z: [INFO]  *DBG* <0.277.3> got {'EXIT',<0.278.3>,
2023-08-28T04:42:50.315452760Z: [INFO]                          {{badmatch,nil},
2023-08-28T04:42:50.315460460Z: [INFO]                           [{'Elixir.Tds.Tls','assert_connected!',1,
2023-08-28T04:42:50.315465160Z: [INFO]                                [{file,"lib/tds/tls.ex"},{line,86}]},
2023-08-28T04:42:50.315470260Z: [INFO]                            {'Elixir.Tds.Tls',send,2,
2023-08-28T04:42:50.315475360Z: [INFO]                                [{file,"lib/tds/tls.ex"},{line,41}]},
2023-08-28T04:42:50.315480460Z: [INFO]                            {tls_sender,send_tls_alert,2,
2023-08-28T04:42:50.315484861Z: [INFO]                                [{file,"tls_sender.erl"},{line,489}]},
2023-08-28T04:42:50.315489961Z: [INFO]                            {tls_sender,connection,3,
2023-08-28T04:42:50.315494761Z: [INFO]                                [{file,"tls_sender.erl"},{line,277}]},
2023-08-28T04:42:50.315499561Z: [INFO]                            {gen_statem,loop_state_callback,11,
2023-08-28T04:42:50.315518161Z: [INFO]                                [{file,"gen_statem.erl"},{line,1426}]},
2023-08-28T04:42:50.315522561Z: [INFO]                            {proc_lib,init_p_do_apply,3,
2023-08-28T04:42:50.315526662Z: [INFO]                                [{file,"proc_lib.erl"},{line,240}]}]}}
2023-08-28T04:42:50.315539562Z: [INFO]  *DBG* <0.277.3> new state {state,
2023-08-28T04:42:50.315546362Z: [INFO]                             {<0.277.3>,tls_dyn_connection_sup},
2023-08-28T04:42:50.315549562Z: [INFO]                             one_for_all,
2023-08-28T04:42:50.315552462Z: [INFO]                             {[receiver],
2023-08-28T04:42:50.315555262Z: [INFO]                              #{receiver =>
2023-08-28T04:42:50.315558262Z: [INFO]                                 {child,<0.279.3>,receiver,
2023-08-28T04:42:50.315561262Z: [INFO]                                  {ssl_gen_statem,start_link,undefined},
2023-08-28T04:42:50.315564362Z: [INFO]                                  temporary,true,5000,worker,
2023-08-28T04:42:50.315567362Z: [INFO]                                  [ssl_gen_statem,tls_connection,
2023-08-28T04:42:50.315570363Z: [INFO]                                   tls_connection_1_3]}}},
2023-08-28T04:42:50.315573363Z: [INFO]                             undefined,0,3600,[],0,any_significant,
2023-08-28T04:42:50.315576163Z: [INFO]                             tls_dyn_connection_sup,[]}
2023-08-28T04:42:50.315579563Z: [INFO]  *DBG* <0.277.3> got {'EXIT',<0.279.3>,{shutdown,normal}}
2023-08-28T04:42:53.071126125Z: [INFO]  04:42:53.070 [error] GenServer #PID<0.309.3> terminating

Logger.configure(level: :debug, truncate: :infinity) in iex

2023-08-28T05:43:46.619701740Z 05:43:46.603 [error] GenServer #PID<0.3123.0> terminating
2023-08-28T05:43:46.619757642Z ** (stop) :tcp_closed
2023-08-28T05:43:46.619767042Z Last message: {:tcp_closed, #Port<0.350>}
2023-08-28T05:43:46.619783042Z State: %Tds.Tls{socket: #Port<0.350>, ssl_opts: [cacerts: [{:cert, <<48, 130, 3, 148, 48, 130, 

%Tds.Tls{
  socket: Port<0.124>,
  ssl_opts: [cacerts: 
    [{:cert, <<48, 130, 3, 148, 48, 130, 2, 124, 160, 3, 2, 1, 2, 2, 10, 49, 245, 228, 98, 12, 108, 88, 237, 214, 216, 48, 13, 6, 9, 42, 134, 72, 134, 247, 13, 1, 1, 11, 5, 0, 48, 103, 49, 11, ...>>],
    customize_hostname_check: [match_fun: Function<41.3316493/2 in :erl_eval.expr/6>], 
    verify_fun: {&:ssl_verify_hostname.verify_fun/3, []}, 
    verify: :verify_peer, 
    active: false, 
    cb_info: {Tds.Tls, :tcp, :tcp_closed, :tcp_error}
  ],
  owner_pid: PID<0.2478.0>, handshake?: false, buffer: nil
}