Автостарт сервиса после полного старта mongodb

#linux #ubuntu #mongodb #systemd

Система: ubuntu 16.04.1 (для запуска сервисов используется systemd).

Имеем: приложение-сервис, которое зависит от mongodb. Приложение и mongodb запускаются
автоматически, на старте ubuntu. В .service файле приложения прописана зависимость:

After=network.target mongod.service


При этом, вероятно, из-за того, что mongodb сразу после старта ещё не готова принимать
подключения, приложение падает с ошибкой "невозможно подключиться к бд".

Каким образом лучше выполнить задержку до полного старта mongodb, либо другим способом
определить готовность mongodb используя возможности systemd?
    

Ответы

Ответ 1

В этом случае воспользуйтесь ExecStartPost и netcat:

ExecStart=
ExecStartPost=/bin/sleep 1s
ExecStartPost=/usr/bin/nc -z host port


Где host port - адрес и порт mongodb.

systemd будет ожидать выполнения всех команд до запуска зависимых сервисов.

В случае если время старта может "плавать" поможет:

until [[ $(nc -z  ) -eq 1 ]]; do sleep 1s; done


until будет вызывать sleep до тех пор пока netcat возвращает -1.

ExecStartPre и ExecStartPost часть жизненного цикла запуска unita


  ExecStartPre=, ExecStartPost=
  
  Additional commands that are executed before or after the command in ExecStart=,
respectively. Syntax is the same as for ExecStart=, except that multiple command lines
are allowed and the commands are executed one after the other, serially.
  
  If any of those commands (not prefixed with "-") fail, the rest are not executed
and the unit is considered failed.
  
  ExecStart= commands are only run after all ExecStartPre= commands that were not
prefixed with a "-" exit successfully.
  
  ExecStartPost= commands are only run after the service has started successfully,
as determined by Type= (i.e. the process has been started for Type=simple or Type=idle,
the process exits successfully for Type=oneshot, the initial process exits successfully
for Type=forking, "READY=1" is sent for Type=notify, or the BusName= has been taken
for Type=dbus).
  
  Note that ExecStartPre= may not be used to start long-running processes. All processes
forked off by processes invoked via ExecStartPre= will be killed before the next service
process is run.
  
  Note that if any of the commands specified in ExecStartPre=, ExecStart=, or ExecStartPost=
fail (and are not prefixed with "-", see above) or time out before the service is fully
up, execution continues with commands specified in ExecStopPost=, the commands in ExecStop=
are skipped.


В случае если между unit'ами указана зависимость Before или After systemd откладывает
старт зависящего сервиса до тех пор пока другой не запустится:


  Before=, After=
  
  A space-separated list of unit names. Configures ordering dependencies between
units. If a unit foo.service contains a setting Before=bar.service and both units are
being started, bar.service's start-up is delayed until foo.service is started up. Note
that this setting is independent of and orthogonal to the requirement dependencies
as configured by Requires=. It is a common pattern to include a unit name in both the
After= and Requires= option, in which case the unit listed will be started before the
unit that is configured with these options. This option may be specified more than
once, in which case ordering dependencies for all listed names are created. After=
is the inverse of Before=, i.e. while After= ensures that the configured unit is started
after the listed unit finished starting up, Before= ensures the opposite, i.e. that
the configured unit is fully started up before the listed unit is started. Note that
when two units with an ordering dependency between them are shut down, the inverse
of the start-up order is applied. i.e. if a unit is configured with After= on another
unit, the former is stopped before the latter if both are shut down. Given two units
with any ordering dependency between them, if one unit is shut down and the other is
started up, the shutdown is ordered before the start-up. It doesn't matter if the ordering
dependency is After= or Before=. It also doesn't matter which of the two is shut down,
as long as one is shut down and the other is started up. The shutdown is ordered before
the start-up in all cases. If two units have no ordering dependencies between them,
they are shut down or started up simultaneously, and no ordering takes place.