Merge pull request #25197 from sfsmithcha/add_services_guide
author merge: add services guide to manage a swarm
This commit is contained in:
Charles Smith
GitHub
commit
8b69d50c79
1 changed files with 328 additions and 0 deletions
328
docs/swarm/services.md
Normal file
328
docs/swarm/services.md
Normal file
|
|
@ -0,0 +1,328 @@
|
|||
<!--[metadata]>
|
||||
+++
|
||||
title = "Deploy services to a swarm"
|
||||
description = "Deploy services to a swarm"
|
||||
keywords = ["guide", "swarm mode", "swarm", "service"]
|
||||
[menu.main]
|
||||
identifier="services-guide"
|
||||
parent="engine_swarm"
|
||||
weight=15
|
||||
+++
|
||||
<![end-metadata]-->
|
||||
|
||||
# Deploy services to a swarm
|
||||
|
||||
When you are running Docker Engine in swarm mode, you run
|
||||
`docker service create` to deploy your application in the swarm. The swarm
|
||||
manager accepts the service description as the desired state for your
|
||||
application. The built-in swarm orchestrator and scheduler deploy your
|
||||
application to nodes in your swarm to achieve and maintain the desired state.
|
||||
|
||||
For an overview of how services work, refer to [How services work](how-swarm-mode-works/services.md).
|
||||
|
||||
This guide assumes you are working with the Docker Engine running in swarm
|
||||
mode. You must run all `docker service` commands from a manager node.
|
||||
|
||||
If you haven't already, read through [Swarm mode key concepts](key-concepts.md)
|
||||
and [How services work](how-swarm-mode-works/services.md).
|
||||
|
||||
## Create a service
|
||||
|
||||
To create the simplest type of service in a swarm, you only need to supply
|
||||
a container image:
|
||||
|
||||
```bash
|
||||
$ docker service create <IMAGE>
|
||||
```
|
||||
|
||||
The swarm orchestrator schedules one task on an available node. The task invokes
|
||||
a container based upon the image. For example, you could run the following
|
||||
command to create a service of one instance of an nginx web server:
|
||||
|
||||
```bash
|
||||
$ docker service create --name my_web nginx
|
||||
|
||||
anixjtol6wdfn6yylbkrbj2nx
|
||||
```
|
||||
|
||||
In this example the `--name` flag names the service `my_web`.
|
||||
|
||||
To list the service, run `docker service ls` from a manager node:
|
||||
|
||||
```bash
|
||||
$ docker service ls
|
||||
|
||||
ID NAME REPLICAS IMAGE COMMAND
|
||||
anixjtol6wdf my_web 1/1 nginx
|
||||
```
|
||||
|
||||
To make the web server accessible from outside the swarm, you need to
|
||||
[publish the port](#publish-ports-externally-to-the-swarm) where the swarm
|
||||
listens for web requests.
|
||||
|
||||
You can include a command to run inside containers after the image:
|
||||
|
||||
```bash
|
||||
$ docker service create <IMAGE> <COMMAND>
|
||||
```
|
||||
|
||||
For example to start an `alpine` image that runs `ping docker.com`:
|
||||
|
||||
```bash
|
||||
$ docker service create --name helloworld alpine ping docker.com
|
||||
|
||||
9uk4639qpg7npwf3fn2aasksr
|
||||
```
|
||||
|
||||
## Configure the runtime environment
|
||||
|
||||
You can configure the following options for the runtime environment in the
|
||||
container:
|
||||
|
||||
* environment variables using the `--env` flag
|
||||
* the working directory inside the container using the `--workdir` flag
|
||||
* the username or UID using the `--user` flag
|
||||
|
||||
For example:
|
||||
|
||||
```bash
|
||||
$ docker service create --name helloworld \
|
||||
--env MYVAR=myvalue \
|
||||
--workdir /tmp \
|
||||
--user my_user \
|
||||
alpine ping docker.com
|
||||
|
||||
9uk4639qpg7npwf3fn2aasksr
|
||||
```
|
||||
|
||||
## Control service scale and placement
|
||||
|
||||
Swarm mode has two types of services, replicated and global. For replicated
|
||||
services, you specify the number of replica tasks for the swarm manager to
|
||||
schedule onto available nodes. For global services, the scheduler places one
|
||||
task on each available node.
|
||||
|
||||
You control the type of service using the `--mode` flag. If you don't specify a
|
||||
mode, the service defaults to `replicated`. For replicated services, you specify
|
||||
the number of replica tasks you want to start using the `--replicas` flag. For
|
||||
example, to start a replicated nginx service with 3 replica tasks:
|
||||
|
||||
```bash
|
||||
$ docker service create --name my_web --replicas 3 nginx
|
||||
```
|
||||
|
||||
To start a global service on each available node, pass `--mode global` to
|
||||
`docker service create`. Every time a new node becomes available, the scheduler
|
||||
places a task for the global service on the new node. For example to start a
|
||||
service that runs alpine on every node in the swarm:
|
||||
|
||||
```bash
|
||||
$ docker service create --name myservice --mode global alpine top
|
||||
```
|
||||
|
||||
Service constraints let you set criteria for a node to meet before the scheduler
|
||||
deploys a service to the node. You can apply constraints to the
|
||||
service based upon node attributes and metadata or engine metadata. For more
|
||||
information on constraints, refer to the `docker service create` [CLI reference](../reference/commandline/service_create.md).
|
||||
|
||||
|
||||
## Configure service networking options
|
||||
|
||||
Swarm mode lets you network services in a couple of ways:
|
||||
|
||||
* publish ports externally to the swarm using ingress networking
|
||||
* connect services and tasks within the swarm using overlay networks
|
||||
|
||||
### Publish ports externally to the swarm
|
||||
|
||||
You publish service ports externally to the swarm using the `--publish
|
||||
<TARGET-PORT>:<SERVICE-PORT>` flag. When you publish a service port, the swarm
|
||||
makes the service accessible at the target port on every node regardless if
|
||||
there is a task for the service running on the node.
|
||||
|
||||
For example, imagine you want to deploy a 3-replica nginx service to a 10-node
|
||||
swarm as follows:
|
||||
|
||||
```bash
|
||||
docker service create --name my_web --replicas 3 --publish 8080:80 nginx
|
||||
```
|
||||
|
||||
The scheduler will deploy nginx tasks to a maximum of 3 nodes. However, the
|
||||
swarm makes nginx port 80 from the task container accessible at port 8080 on any
|
||||
node in the swarm. You can direct `curl` at port 8080 of any node in the swarm
|
||||
to access the web server:
|
||||
|
||||
```bash
|
||||
$ curl localhost:8080
|
||||
|
||||
<!DOCTYPE html>
|
||||
<html>
|
||||
<head>
|
||||
<title>Welcome to nginx!</title>
|
||||
<style>
|
||||
body {
|
||||
width: 35em;
|
||||
margin: 0 auto;
|
||||
font-family: Tahoma, Verdana, Arial, sans-serif;
|
||||
}
|
||||
</style>
|
||||
</head>
|
||||
<body>
|
||||
<h1>Welcome to nginx!</h1>
|
||||
<p>If you see this page, the nginx web server is successfully installed and
|
||||
working. Further configuration is required.</p>
|
||||
|
||||
<p>For online documentation and support please refer to
|
||||
<a href="http://nginx.org/">nginx.org</a>.<br/>
|
||||
Commercial support is available at
|
||||
<a href="http://nginx.com/">nginx.com</a>.</p>
|
||||
|
||||
<p><em>Thank you for using nginx.</em></p>
|
||||
</body>
|
||||
</html>
|
||||
```
|
||||
|
||||
### Add an overlay network
|
||||
|
||||
Use overlay networks to connect one or more services within the swarm.
|
||||
|
||||
First, create an overlay network on a manager node the `docker network create`
|
||||
command:
|
||||
|
||||
```bash
|
||||
$ docker network create --driver overlay my-network
|
||||
|
||||
etjpu59cykrptrgw0z0hk5snf
|
||||
```
|
||||
|
||||
After you create an overlay network in swarm mode, all manager nodes have access
|
||||
to the network.
|
||||
|
||||
When you create a service and pass the `--network` flag to attach the service to
|
||||
the overlay network:
|
||||
|
||||
```bash
|
||||
$ docker service create \
|
||||
--replicas 3 \
|
||||
--network my-multi-host-network \
|
||||
--name my-web \
|
||||
nginx
|
||||
|
||||
716thylsndqma81j6kkkb5aus
|
||||
```
|
||||
|
||||
The swarm extends `my-network` to each node running the service.
|
||||
|
||||
<!-- TODO when overlay-security-model is published
|
||||
For more information, refer to [Note on Docker 1.12 Overlay Network Security Model](../userguide/networking/overlay-security-model.md).-->
|
||||
|
||||
## Configure update behavior
|
||||
|
||||
When you create a service, you can specify a rolling update behavior for how the
|
||||
swarm should apply changes to the service when you run `docker service update`.
|
||||
You can also specify these flags as part of the update, as arguments to
|
||||
`docker service update`.
|
||||
|
||||
The `--update-delay` flag configures the time delay between updates to a service
|
||||
task or sets of tasks. You can describe the time `T` as a combination of the
|
||||
number of seconds `Ts`, minutes `Tm`, or hours `Th`. So `10m30s` indicates a 10
|
||||
minute 30 second delay.
|
||||
|
||||
By default the scheduler updates 1 task at a time. You can pass the
|
||||
`--update-parallelism` flag to configure the maximum number of service tasks
|
||||
that the scheduler updates simultaneously.
|
||||
|
||||
When an update to an individual task returns a state of `RUNNING`, the scheduler
|
||||
continues the update by continuing to another task until all tasks are updated.
|
||||
If, at any time during an update a task returns `FAILED`, the scheduler pauses
|
||||
the update. You can control the behavior using the `--update-failure-action`
|
||||
flag for `docker service create` or `docker service update`.
|
||||
|
||||
In the example service below, the scheduler applies updates to a maximum of 2
|
||||
replicas at a time. When an updated task returns either `RUNNING` or `FAILED`,
|
||||
the scheduler waits 10 seconds before stopping the next task to update:
|
||||
|
||||
```bash
|
||||
$ docker service create \
|
||||
--replicas 10 \
|
||||
--name my_web \
|
||||
--update-delay 10s \
|
||||
--update-parallelism 2 \
|
||||
--update-failure-action continue \
|
||||
alpine
|
||||
|
||||
0u6a4s31ybk7yw2wyvtikmu50
|
||||
```
|
||||
|
||||
## Configure mounts
|
||||
|
||||
You can create two types of mounts for services in a swarm, `volume` mounts or
|
||||
`bind` mounts. You pass the `--mount` flag when you create a service. The
|
||||
default is a volume mount if you don't specify a type.
|
||||
|
||||
* Volumes are storage that remain alive after a container for a task has
|
||||
been removed. The preferred method to mount volumes is to leverage an existing
|
||||
volume:
|
||||
|
||||
```bash
|
||||
$ docker service create \
|
||||
--mount src=<VOLUME-NAME>,dst=<CONTAINER-PATH> \
|
||||
--name myservice \
|
||||
<IMAGE>
|
||||
```
|
||||
|
||||
For more information on how to create a volume, see the `volume create` [CLI reference](../reference/commandline/volume_create.md).
|
||||
|
||||
The following method creates the volume at deployment time when the scheduler
|
||||
dispatches a task, just before the starting the container:
|
||||
|
||||
```bash
|
||||
$ docker service create \
|
||||
--mount type=volume,src=<VOLUME-NAME>,dst=<CONTAINER-PATH>,volume-driver=<DRIVER>,volume-opt=<KEY0>=<VALUE0>,volume-opt=<KEY1>=<VALUE1>
|
||||
--name myservice \
|
||||
<IMAGE>
|
||||
```
|
||||
|
||||
* Bind mounts are file system paths from the host where the scheduler deploys
|
||||
the container for the task. Docker mounts the path into the container. The
|
||||
file system path must exist before the swarm initializes the container for the
|
||||
task.
|
||||
|
||||
The following examples show bind mount syntax:
|
||||
|
||||
```bash
|
||||
# Mount a read-write bind
|
||||
$ docker service create \
|
||||
--mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH> \
|
||||
--name myservice \
|
||||
<IMAGE>
|
||||
|
||||
# Mount a read-only bind
|
||||
$ docker service create \
|
||||
--mount type=bind,src=<HOST-PATH>,dst=<CONTAINER-PATH>,readonly \
|
||||
--name myservice \
|
||||
<IMAGE>
|
||||
```
|
||||
|
||||
>**Important note:** Bind mounts can be useful but they are also dangerous. In
|
||||
most cases, we recommend that you architect your application such that mounting
|
||||
paths from the host is unnecessary. The main risks include the following:<br />
|
||||
> <br />
|
||||
> If you bind mount a host path into your service’s containers, the path
|
||||
> must exist on every machine. The Docker swarm mode scheduler can schedule
|
||||
> containers on any machine that meets resource availability requirements
|
||||
> and satisfies all `--constraint`s you specify.<br />
|
||||
> <br />
|
||||
> The Docker swarm mode scheduler may reschedule your running service
|
||||
> containers at any time if they become unhealthy or unreachable.<br />
|
||||
> <br />
|
||||
> Host bind mounts are completely non-portable. When you use bind mounts,
|
||||
> there is no guarantee that your application will run the same way in
|
||||
> development as it does in production.
|
||||
|
||||
|
||||
## Learn More
|
||||
|
||||
* [Swarm administration guide](admin_guide.md)
|
||||
* [Docker Engine command line reference](../reference/commandline/index.md)
|
||||
* [Swarm mode tutorial](swarm-tutorial/index.md)
|
||||
Loading…
Reference in a new issue