There is a not-insignificant performance overhead for all containers (if
containerd is a child of Docker, which is the current setup) if systemd
sets rlimits on the main Docker daemon process (because the limits
propogate to all children).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 68e1541)
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>

Systemd sets a default of 512 tasks, which is far
too low to run many containers.

Note that TasksMax is only supported on systemd 226
and above.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 82fe967)
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>

We need to add delegate yes to docker's service file so that it can
manage the cgroups of the processes that it launches without systemd
interfering with them and moving the processes after it is reloaded.

       Delegate=
           Turns on delegation of further resource control partitioning to
           processes of the unit. For unprivileged services (i.e. those
           using the User= setting), this allows processes to create a
           subhierarchy beneath its control group path. For privileged
           services and scopes, this ensures the processes will have all
           control group controllers enabled.

This is the proper fix for issue moby/moby#20152

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit e134e66)
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>

Change the kill mode to process so that systemd does not kill container
processes when the daemon is shutdown but only the docker daemon

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit d736ae9)
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>

This adds support for reloading the docker daemon
(SIGHIUP) so that changes in '/etc/docker/daemon.json'
can be loaded at runtime by reloading the service
through systemd ('systemctl reload docker')

Before this change, systemd would output an error
that "reloading" is not supported for the docker
service;

  systemctl reload docker
  Failed to reload docker.service: Job type reload is not applicable for unit docker.service.

After this change, the docker daemon can be reloaded
through 'systemctl reload docker', which reloads
the configuration;

  journalctl -f -u docker.service

  May 02 03:49:20 testing systemd[1]: Reloading Docker Application Container Engine.
  May 02 03:49:20 testing docker[28496]: time="2016-05-02T03:49:20.143964103-04:00" level=info msg="Got signal to reload configuration, reloading from: /etc/docker/daemon.json"
  May 02 03:49:20 testing systemd[1]: Reloaded Docker Application Container Engine.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 3e1b508)
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>

Note that StartLimit* options were moved from "Service" to "Unit" in systemd 229
(systemd/systemd@6bf0f40)
both the old, and new location are accepted by systemd 229 and up, so using the old location
to make them work for either version of systemd.

StartLimitInterval was renamed to StartLimitIntervalSec in systemd 230
(systemd/systemd@f0367da)
both the old, and new name are accepted by systemd 230 and up, so using the old name to make
this option work for either version of systemd.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 2c2bfea)
Signed-off-by: Eli Uriegas <eli.uriegas@docker.com>