Swarm task states
Estimated reading time: 2 minutesDocker 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
or the UCP web UI or CLI. - 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
, andCOMPLETE
.
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 . |
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.…"