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Update services.md (#4457)

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Wang Jie 2017-09-12 00:51:36 +08:00 committed by Gwendolynne Barr
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engine/swarm/how-swarm-mode-works/services.md
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@ -33,15 +33,15 @@ Each of the three instances of the listener is a task in the swarm.
![services diagram](../images/services-diagram.png) ![services diagram](../images/services-diagram.png)
A container is an isolated process. In the swarm mode model, each task invokes A container is an isolated process. In the swarm mode model, each task invokes
exactly one container. A task is analogous to a “slot” where the scheduler exactly one container. A task is analogous to a “slot” where the scheduler
places a container. Once the container is live, the scheduler recognizes that places a container. Once the container is live, the scheduler recognizes that
the task is in a running state. If the container fails health checks or the task is in a running state. If the container fails health checks or
terminates, the task terminates. terminates, the task terminates.
## Tasks and scheduling ## Tasks and scheduling
A task is the atomic unit of scheduling within a swarm. When you declare a A task is the atomic unit of scheduling within a swarm. When you declare a
desired service state by creating or updating a service, the orchestrator desired service state by creating or updating a service, the orchestrator
realizes the desired state by scheduling tasks. For instance, you define a realizes the desired state by scheduling tasks. For instance, you define a
service that instructs the orchestrator to keep three instances of an HTTP service that instructs the orchestrator to keep three instances of an HTTP
@ -52,14 +52,14 @@ fails its health check or crashes, the orchestrator creates a new replica task
that spawns a new container. that spawns a new container.
A task is a one-directional mechanism. It progresses monotonically through a A task is a one-directional mechanism. It progresses monotonically through a
series of states: assigned, prepared, running, etc. If the task fails the series of states: assigned, prepared, running, etc. If the task fails the
orchestrator removes the task and its container and then creates a new task to orchestrator removes the task and its container and then creates a new task to
replace it according to the desired state specified by the service. replace it according to the desired state specified by the service.
The underlying logic of Docker swarm mode is a general purpose scheduler and The underlying logic of Docker swarm mode is a general purpose scheduler and
orchestrator. The service and task abstractions themselves are unaware of the orchestrator. The service and task abstractions themselves are unaware of the
containers they implement. Hypothetically, you could implement other types of containers they implement. Hypothetically, you could implement other types of
tasks such as virtual machine tasks or non-containerized process tasks. The tasks such as virtual machine tasks or non-containerized process tasks. The
scheduler and orchestrator are agnostic about the type of task. However, the scheduler and orchestrator are agnostic about the type of task. However, the
current version of Docker only supports container tasks. current version of Docker only supports container tasks.
@ -74,7 +74,7 @@ A service may be configured in such a way that no node currently in the
swarm can run its tasks. In this case, the service remains in state `pending`. swarm can run its tasks. In this case, the service remains in state `pending`.
Here are a few examples of when a service might remain in state `pending`. Here are a few examples of when a service might remain in state `pending`.
**Note**: If your only intention is to prevent a service from > **Note**: If your only intention is to prevent a service from
being deployed, scale the service to 0 instead of trying to configure it in being deployed, scale the service to 0 instead of trying to configure it in
such a way that it will remain in `pending`. such a way that it will remain in `pending`.
@ -118,7 +118,7 @@ in gray.
![global vs replicated services](../images/replicated-vs-global.png) ![global vs replicated services](../images/replicated-vs-global.png)
## Learn More ## Learn more
* Read about how swarm mode [nodes](nodes.md) work. * Read about how swarm mode [nodes](nodes.md) work.
* Learn how [PKI](pki.md) works in swarm mode. * Learn how [PKI](pki.md) works in swarm mode.