解决 Logger 后端应用程序启动时的错误及其未初始化的依赖项之一？
Resolving errors on application start for Logger backend and one of its dependencies not being initialized?
我在我的应用程序中使用这个 Logger 后端：
在应用程序的 mix.exs 文件中，在 application 函数中，:logger_logstash_backend 包含在 :applications 键中（在 :timex 之后，它位于依赖）。
当我通过 iex -S mix 启动我的应用程序时，我看到很多错误，如下所示：
15:49:48.306 registered_name=Logger function=report_error/5 module=gen_event line=747 file=gen_event.erl pid=<0.2656.0> [error] :gen_event handler {LoggerLogstashBackend, :logstash_log} installed in Logger terminating
** (ArgumentError) argument error
(stdlib) :ets.lookup(:tzdata_current_release, :release_version)
lib/tzdata/release_reader.ex:74: Tzdata.ReleaseReader.current_release_from_table/0
lib/tzdata/release_reader.ex:17: Tzdata.ReleaseReader.simple_lookup/1
lib/tzdata/release_reader.ex:9: Tzdata.ReleaseReader.zone_and_link_list/0
lib/tzdata.ex:61: Tzdata.zone_exists?/1
lib/timezone/timezone.ex:358: Timex.Timezone.resolve/3
lib/logger_logstash_backend.ex:73: LoggerLogstashBackend.log_event/5
lib/logger_logstash_backend.ex:40: LoggerLogstashBackend.handle_event/2
(stdlib) gen_event.erl:577: :gen_event.server_update/4
(stdlib) gen_event.erl:559: :gen_event.server_notify/4
(stdlib) gen_event.erl:561: :gen_event.server_notify/4
(stdlib) gen_event.erl:300: :gen_event.handle_msg/6
(stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Last message: {:info, #PID<0.63.0>, {Logger, ["Application ", "logger", " started at " | ":nonode@nohost"], {{2020, 1, 6}, {15, 49, 48, 224}}, [function: "info_started/2", module: :application_controller, line: 1926, file: "application_controller.erl", pid: #PID<0.43.0>]}}
State: %{ex_jsx_opts: [:uescape], host: '127.0.0.1', level: :info, metadata: [], name: :logstash_log, port: 4201, socket: #Port<0.2458>, type: "elixir"}
15:49:48.307 function=error_info/7 module=gen_server line=888 file=gen_server.erl pid=<0.2659.0> [error] GenServer #PID<0.2659.0> terminating
** (stop) {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}
Last message: {:gen_event_EXIT, {LoggerLogstashBackend, :logstash_log}, {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}}
State: {Logger, {LoggerLogstashBackend, :logstash_log}}
15:49:48.315 initial_call=Logger.Watcher.init/1 function=crash_report/4 module=proc_lib line=508 file=proc_lib.erl pid=<0.2659.0> [error] Process #PID<0.2659.0> terminating
** (exit) {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}
(stdlib) gen_server.erl:751: :gen_server.handle_common_reply/8
(stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Initial Call: Logger.Watcher.init/1
Ancestors: [Logger.BackendSupervisor, Logger.Supervisor, #PID<0.2654.0>]
Message Queue Length: 0
Messages: []
Links: [#PID<0.2658.0>, #PID<0.2656.0>]
Dictionary: []
Trapping Exits: true
Status: :running
Heap Size: 4185
Stack Size: 27
Reductions: 57169
15:49:48.316 function=do_restart/3 module=supervisor line=713 file=supervisor.erl pid=<0.2658.0> [error] Child {LoggerLogstashBackend, :logstash_log} of Supervisor Logger.BackendSupervisor terminated
** (exit) {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}
Pid: #PID<0.2659.0>
Start Call: Logger.Watcher.start_link({Logger, {LoggerLogstashBackend, :logstash_log}, {LoggerLogstashBackend, :logstash_log}})
Restart: :transient
Shutdown: 5000
Type: :worker
15:49:48.316 function=report_progress/2 module=supervisor line=1419 file=supervisor.erl pid=<0.2658.0> [info] Child {LoggerLogstashBackend, :logstash_log} of Supervisor Logger.BackendSupervisor started
Pid: #PID<0.2678.0>
Start Call: Logger.Watcher.start_link({Logger, {LoggerLogstashBackend, :logstash_log}, {LoggerLogstashBackend, :logstash_log}})
Restart: :transient
Shutdown: 5000
Type: :worker
（最后一个事件不是错误。）
错误似乎是由于依赖 tzdata 的后端已经启动并且其 ETS table 存在。
直到今天我一直在忽略这些错误。今天，我的整个应用程序第一次无法启动，因为在足够短的时间内终于出现了足够多的上述错误，以至于监督树本身崩溃了。
我尝试将后端应用程序从 :applications 键移动到 start_phase 函数，但这似乎根本没有帮助。我猜这是因为后端应用程序正在由 Logger 本身启动。
如何解决或避免这些错误？ 应该（理想情况下）在我的应用程序或后端中更改什么以避免此问题或类似问题？
后端完全依赖Timex和tzdata的问题吗？或者有什么方法可以让 Logger 启动后端，然后它自己等待 tzdata（或 Timex）完成加载，然后才开始正常处理日志事件？
后台的GitHub项目似乎已经有一段时间没有积极维护了。我目前实际上正在使用代码的个人分支。所以我愿意接受更改后端代码的建议。
我之前在 Elixir Forum 上发布过关于此的主题：
虽然错误消息可能看起来有点混乱，但您不应将 :logger_logstash_backend 包含到 applications 中。 LoggerLogstashBackend 的整个源代码是 implementation of :gen_event, as nearly all the logger backends. It does not implement Application 行为，也不打算用作应用程序。
您的 applications 应该看起来像 [:logger, :timex]，正如 README 中明确说明的那样。
我不确定为什么它不抱怨尝试启动不存在的应用程序，可能是因为 :gen_event 的默认实现显然有 start_link/2（ 或 use Timex 注入它 it does not.)
UPD 将 :applications 更改为 :extra_applications，或明确启动 :tzdata 应用程序。 Timer 依赖它，并且 :applications 放弃所有自动启动的应用程序链，以支持那里明确说明的内容。
Timex 无法启动，因为它依赖于未启动的 :tzdata 应用程序。
我能够 resolve/prevent 所有这些错误（以及解决第一组后出现的一些新错误）。
我从 :applications 密钥中删除了后端 – 无论如何这样做很好。稍后我将尝试更普遍地清理依赖项，例如完全删除 :applications 键并仅将必要的 'extra' 应用程序添加到 :extra_applications 键。 （我的应用程序比 Elixir 中的那些更改更旧；因此这个 code/configuration 的陈旧状态。）
我修改了 Logger 配置以不包含此后端。相反，我为应用程序添加了一个 'start phase'；在 mix.exs:
# Start `logger_logstash_backend` after `timex` (and `tzdata`) have been started:
start_phases: [{:logger_logstash_backend, []}]
在我的主应用模块中：
def start_phase(:logger_logstash_backend, _start_type, _phase_args) do
IO.puts "Starting application start phase `:logger_logstash_backend`"
case Application.fetch_env(:my_app, :logger_logstash_backend) do
:error ->
IO.puts "No configuration value was found for the Logger Logstash backend."
{:ok, options} ->
backend = {LoggerLogstashBackend, :logstash_log}
# From the docs for `Logger.add_backend`:
#
# > Backends added by this function are not persisted. Therefore
# > if the Logger application or supervision tree is restarted,
# > the backend won't be available. If you need this guarantee,
# > then configure the backend via the application environment.
#
# This shouldn't be an issue for us as the `Logger` application and supervision tree don't seem
# to have ever needed to be restarted; just started normally when the app is started, i.e. when
# running the app locally in a `:dev` environment or when starting a new instance in production.
Logger.add_backend(backend)
Logger.configure_backend(backend, options)
end
:ok
end
这 感觉 喜欢 'right way' 解决这样的问题，例如应用程序或其他 'server' 进程需要在应用程序启动期间启动，但 在 它所依赖的其他应用程序或服务器进程之后。
我在我的应用程序中使用这个 Logger 后端：
在应用程序的 mix.exs 文件中，在 application 函数中，:logger_logstash_backend 包含在 :applications 键中（在 :timex 之后，它位于依赖）。
当我通过 iex -S mix 启动我的应用程序时，我看到很多错误，如下所示：
15:49:48.306 registered_name=Logger function=report_error/5 module=gen_event line=747 file=gen_event.erl pid=<0.2656.0> [error] :gen_event handler {LoggerLogstashBackend, :logstash_log} installed in Logger terminating
** (ArgumentError) argument error
(stdlib) :ets.lookup(:tzdata_current_release, :release_version)
lib/tzdata/release_reader.ex:74: Tzdata.ReleaseReader.current_release_from_table/0
lib/tzdata/release_reader.ex:17: Tzdata.ReleaseReader.simple_lookup/1
lib/tzdata/release_reader.ex:9: Tzdata.ReleaseReader.zone_and_link_list/0
lib/tzdata.ex:61: Tzdata.zone_exists?/1
lib/timezone/timezone.ex:358: Timex.Timezone.resolve/3
lib/logger_logstash_backend.ex:73: LoggerLogstashBackend.log_event/5
lib/logger_logstash_backend.ex:40: LoggerLogstashBackend.handle_event/2
(stdlib) gen_event.erl:577: :gen_event.server_update/4
(stdlib) gen_event.erl:559: :gen_event.server_notify/4
(stdlib) gen_event.erl:561: :gen_event.server_notify/4
(stdlib) gen_event.erl:300: :gen_event.handle_msg/6
(stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Last message: {:info, #PID<0.63.0>, {Logger, ["Application ", "logger", " started at " | ":nonode@nohost"], {{2020, 1, 6}, {15, 49, 48, 224}}, [function: "info_started/2", module: :application_controller, line: 1926, file: "application_controller.erl", pid: #PID<0.43.0>]}}
State: %{ex_jsx_opts: [:uescape], host: '127.0.0.1', level: :info, metadata: [], name: :logstash_log, port: 4201, socket: #Port<0.2458>, type: "elixir"}
15:49:48.307 function=error_info/7 module=gen_server line=888 file=gen_server.erl pid=<0.2659.0> [error] GenServer #PID<0.2659.0> terminating
** (stop) {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}
Last message: {:gen_event_EXIT, {LoggerLogstashBackend, :logstash_log}, {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}}
State: {Logger, {LoggerLogstashBackend, :logstash_log}}
15:49:48.315 initial_call=Logger.Watcher.init/1 function=crash_report/4 module=proc_lib line=508 file=proc_lib.erl pid=<0.2659.0> [error] Process #PID<0.2659.0> terminating
** (exit) {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}
(stdlib) gen_server.erl:751: :gen_server.handle_common_reply/8
(stdlib) proc_lib.erl:249: :proc_lib.init_p_do_apply/3
Initial Call: Logger.Watcher.init/1
Ancestors: [Logger.BackendSupervisor, Logger.Supervisor, #PID<0.2654.0>]
Message Queue Length: 0
Messages: []
Links: [#PID<0.2658.0>, #PID<0.2656.0>]
Dictionary: []
Trapping Exits: true
Status: :running
Heap Size: 4185
Stack Size: 27
Reductions: 57169
15:49:48.316 function=do_restart/3 module=supervisor line=713 file=supervisor.erl pid=<0.2658.0> [error] Child {LoggerLogstashBackend, :logstash_log} of Supervisor Logger.BackendSupervisor terminated
** (exit) {:EXIT, {:badarg, [{:ets, :lookup, [:tzdata_current_release, :release_version], []}, {Tzdata.ReleaseReader, :current_release_from_table, 0, [file: 'lib/tzdata/release_reader.ex', line: 74]}, {Tzdata.ReleaseReader, :simple_lookup, 1, [file: 'lib/tzdata/release_reader.ex', line: 17]}, {Tzdata.ReleaseReader, :zone_and_link_list, 0, [file: 'lib/tzdata/release_reader.ex', line: 9]}, {Tzdata, :zone_exists?, 1, [file: 'lib/tzdata.ex', line: 61]}, {Timex.Timezone, :resolve, 3, [file: 'lib/timezone/timezone.ex', line: 358]}, {LoggerLogstashBackend, :log_event, 5, [file: 'lib/logger_logstash_backend.ex', line: 73]}, {LoggerLogstashBackend, :handle_event, 2, [file: 'lib/logger_logstash_backend.ex', line: 40]}, {:gen_event, :server_update, 4, [file: 'gen_event.erl', line: 577]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 559]}, {:gen_event, :server_notify, 4, [file: 'gen_event.erl', line: 561]}, {:gen_event, :handle_msg, 6, [file: 'gen_event.erl', line: 300]}, {:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 249]}]}}
Pid: #PID<0.2659.0>
Start Call: Logger.Watcher.start_link({Logger, {LoggerLogstashBackend, :logstash_log}, {LoggerLogstashBackend, :logstash_log}})
Restart: :transient
Shutdown: 5000
Type: :worker
15:49:48.316 function=report_progress/2 module=supervisor line=1419 file=supervisor.erl pid=<0.2658.0> [info] Child {LoggerLogstashBackend, :logstash_log} of Supervisor Logger.BackendSupervisor started
Pid: #PID<0.2678.0>
Start Call: Logger.Watcher.start_link({Logger, {LoggerLogstashBackend, :logstash_log}, {LoggerLogstashBackend, :logstash_log}})
Restart: :transient
Shutdown: 5000
Type: :worker
（最后一个事件不是错误。）
错误似乎是由于依赖 tzdata 的后端已经启动并且其 ETS table 存在。
直到今天我一直在忽略这些错误。今天，我的整个应用程序第一次无法启动，因为在足够短的时间内终于出现了足够多的上述错误，以至于监督树本身崩溃了。
我尝试将后端应用程序从 :applications 键移动到 start_phase 函数，但这似乎根本没有帮助。我猜这是因为后端应用程序正在由 Logger 本身启动。
如何解决或避免这些错误？ 应该（理想情况下）在我的应用程序或后端中更改什么以避免此问题或类似问题？
后端完全依赖Timex和tzdata的问题吗？或者有什么方法可以让 Logger 启动后端，然后它自己等待 tzdata（或 Timex）完成加载，然后才开始正常处理日志事件？
后台的GitHub项目似乎已经有一段时间没有积极维护了。我目前实际上正在使用代码的个人分支。所以我愿意接受更改后端代码的建议。
我之前在 Elixir Forum 上发布过关于此的主题：
虽然错误消息可能看起来有点混乱，但您不应将 :logger_logstash_backend 包含到 applications 中。 LoggerLogstashBackend 的整个源代码是 implementation of :gen_event, as nearly all the logger backends. It does not implement Application 行为，也不打算用作应用程序。
您的 applications 应该看起来像 [:logger, :timex]，正如 README 中明确说明的那样。
我不确定为什么它不抱怨尝试启动不存在的应用程序，可能是因为 :gen_event 的默认实现显然有 start_link/2（ 或 it does not.)use Timex 注入它
UPD 将 :applications 更改为 :extra_applications，或明确启动 :tzdata 应用程序。 Timer 依赖它，并且 :applications 放弃所有自动启动的应用程序链，以支持那里明确说明的内容。
Timex 无法启动，因为它依赖于未启动的 :tzdata 应用程序。
我能够 resolve/prevent 所有这些错误（以及解决第一组后出现的一些新错误）。
我从 :applications 密钥中删除了后端 – 无论如何这样做很好。稍后我将尝试更普遍地清理依赖项，例如完全删除 :applications 键并仅将必要的 'extra' 应用程序添加到 :extra_applications 键。 （我的应用程序比 Elixir 中的那些更改更旧；因此这个 code/configuration 的陈旧状态。）
我修改了 Logger 配置以不包含此后端。相反，我为应用程序添加了一个 'start phase'；在 mix.exs:
# Start `logger_logstash_backend` after `timex` (and `tzdata`) have been started:
start_phases: [{:logger_logstash_backend, []}]
在我的主应用模块中：
def start_phase(:logger_logstash_backend, _start_type, _phase_args) do
IO.puts "Starting application start phase `:logger_logstash_backend`"
case Application.fetch_env(:my_app, :logger_logstash_backend) do
:error ->
IO.puts "No configuration value was found for the Logger Logstash backend."
{:ok, options} ->
backend = {LoggerLogstashBackend, :logstash_log}
# From the docs for `Logger.add_backend`:
#
# > Backends added by this function are not persisted. Therefore
# > if the Logger application or supervision tree is restarted,
# > the backend won't be available. If you need this guarantee,
# > then configure the backend via the application environment.
#
# This shouldn't be an issue for us as the `Logger` application and supervision tree don't seem
# to have ever needed to be restarted; just started normally when the app is started, i.e. when
# running the app locally in a `:dev` environment or when starting a new instance in production.
Logger.add_backend(backend)
Logger.configure_backend(backend, options)
end
:ok
end
这 感觉 喜欢 'right way' 解决这样的问题，例如应用程序或其他 'server' 进程需要在应用程序启动期间启动，但 在 它所依赖的其他应用程序或服务器进程之后。