A container that defines no stop timeout of its own always got 10
seconds on Linux, or 30 on Windows, to shut down before being killed.
The value was a constant in the container package, so operators who
wanted a different grace period had to pass `--stop-timeout` on every
container.
Add a `default-stop-timeout` daemon flag and configuration file option
that supplies that fallback. Stopping a container, killing it, and
computing the daemon shutdown timeout take the value from the daemon
configuration when the container has no timeout of its own, so an
explicit per-container timeout still wins and the container
configuration itself stays untouched. The option can be reloaded, and
negative values are rejected.
mergo cannot tell an unset option from a zero value, so a configured
timeout of `0`, meaning "kill immediately", would be replaced by the
non-zero flag default while merging. Remember whether the
configuration file set the option, and restore its value after the
merge.
`ContainerConfig.StopTimeout` in the API documentation no longer
claims a fixed default of 10 seconds, because the fallback is now
whatever `default-stop-timeout` holds.
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>
Paweł Gronowski
99c1a9c778