Swarm task states

Docker lets you create services, which can start tasks. A service is a
description of a desired state, and a task does the work. Work is scheduled on
swarm nodes in this sequence:
Create a service by using 
docker service create.
The request goes to a Docker manager node.
The Docker manager node schedules the service to run on particular nodes.
Each service can start multiple tasks.
Each task has a life cycle, with states like 
NEW, 
PENDING, and 
COMPLETE.
Tasks are execution units that run once to completion. When a task stops, it
isn't executed again, but a new task may take its place.
Tasks advance through a number of states until they complete or fail. Tasks are
initialized in the 
NEW state. The task progresses forward through a number of
states, and its state doesn't go backward. For example, a task never goes from
COMPLETE to 
RUNNING.
Tasks go through the states in the following order:
Task state
Description
NEW
The task was initialized.
PENDING
Resources for the task were allocated.
ASSIGNED
Docker assigned the task to nodes.
ACCEPTED
The task was accepted by a worker node. If a worker node rejects the task, the state changes to 
REJECTED.
READY
The worker node is ready to start the task
PREPARING
Docker is preparing the task.
STARTING
Docker is starting the task.
RUNNING
The task is executing.
COMPLETE
The task exited without an error code.
FAILED
The task exited with an error code.
SHUTDOWN
Docker requested the task to shut down.
REJECTED
The worker node rejected the task.
ORPHANED
The node was down for too long.
REMOVE
The task is not terminal but the associated service was removed or scaled down.
View task state
Run 
docker service ps <service-name> to get the state of a task. The
CURRENT STATE field shows the task's state and how long it's been
there.
$ docker service ps webserver
ID             NAME              IMAGE    NODE        DESIRED STATE  CURRENT STATE            ERROR                              PORTS
owsz0yp6z375   webserver.1       nginx    UbuntuVM    Running        Running 44 seconds ago
j91iahr8s74p    \_ webserver.1   nginx    UbuntuVM    Shutdown       Failed 50 seconds ago    "No such container: webserver.…"
7dyaszg13mw2    \_ webserver.1   nginx    UbuntuVM    Shutdown       Failed 5 hours ago       "No such container: webserver.…"
Where to go next
Learn about swarm tasks