mirror of https://github.com/docker/docs.git
158 lines
5.4 KiB
Markdown
158 lines
5.4 KiB
Markdown
---
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description: Scale your service, spawn new containers
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keywords: spawn, container, service, deploy
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redirect_from:
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- /docker-cloud/feature-reference/service-scaling/
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title: Scale your service
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---
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Docker Cloud makes it easy to spawn new containers of your service to handle
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additional load. Two modes are available to allow you to scale services with
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different configuration requirements.
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## Deployment and scaling modes
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Any service that handles additional load by increasing the number of containers
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of the service is considered "horizontally scalable".
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There are two deployment modes when scaling a service:
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- **Parallel mode** (default): all containers of a service are
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deployed at the same time without any links between them. This is
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the fastest way to deploy, and is the default.
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- **Sequential mode**: each new container is deployed in the service one at a
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time. Each container is linked to all previous containers using service
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links. This makes complex configuration possible within the containers
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startup logic. This mode is explained in detail in the following sections.
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## When should I use Parallel scaling?
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When the containers in a service work independently of each other and do not
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need to coordinate between themselves, they can be scaled up in parallel mode.
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Examples include:
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- Stateless web servers and proxies
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- “Worker” instances that process jobs from a queue
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- “Cron”-style instances that execute periodic tasks
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The default scaling mode is parallel, so no additional configuration is
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required to use this mode.
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## When should I use Sequential scaling?
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Some services require coordination between different containers to ensure that
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the service functions correctly. Many databases, such as MySQL for example,
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require that the containers know about each other at startup time so that
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traffic can be routed to them appropriately. When this is the case, you should
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use [sequential scaling](service-scaling.md#sequential-deployment-and-scaling).
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To allow peer-aware container startup, you can enable sequential scaling mode. See [Sequential Scaling](service-scaling.md#sequential-deployment-and-scaling) for more information.
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## Set the initial number of containers
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When you configure a service in Docker Cloud, you can specify an initial number of containers for the service before you launch.
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Docker Cloud immediately launches as many containers as you specified.
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### Set the initial containers using the API
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You can specify the initial number of containers for a service when deploying it through the API:
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```
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POST /api/app/v1/service/ HTTP/1.1
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{
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"target_num_containers": 2,
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[...]
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}
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```
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If you don’t specify the number of containers to deploy, this command defaults to `1`. See the [API documentation](/apidocs/docker-cloud.md) for more information.
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### Set the initial containers using the CLI
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You can also specify the initial number of containers for a service when deploying it using the CLI:
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```bash
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$ docker-cloud service run -t 2 [...]
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```
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If you don’t specify the number of containers to deploy, the CLI uses the default value of `1`. See the [CLI documentation](/apidocs/docker-cloud.md) for more information.
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## Scale an already running service
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If you need to scale a service up or down while it is running, you can change the number of containers from the service detail page:
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1. Click the slider at the top of the service detail page.
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2. Drag the slider to the number of containers you want.
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3. Click **Scale**.
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The application starts scaling immediately, whether this means starting new containers, or gracefully shutting down existing ones.
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### Scale a running service using the API
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You can scale an already running service through the API:
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```
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PATCH /api/app/v1/service/(uuid)/ HTTP/1.1
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{
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"target_num_containers": 2
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}
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```
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See the [scale a service API documentation](/apidocs/docker-cloud.md#scale-a-service).
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### Scale a running service using the CLI
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You can also scale an already running service using the CLI:
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```bash
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$ docker-cloud service scale (uuid or name) 2
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```
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See the [scale a service CLI documentation](/apidocs/docker-cloud.md#scale-a-service).
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## Sequential deployment and scaling
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When a service with more than one container is deployed using **sequential deployment** mode, the second and subsequent containers are linked to all the
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previous ones using [service links](service-links.md). These links are useful if
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your service needs to know about other instances, for example to allow automatic
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configuration on startup.
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See the [Service links](service-links.md) topic for a list of environment variables that the links create in your containers.
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You can set the **Sequential deployment** setting on the **Service configuration** step of the **Launch new service** wizard:
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### Set the scaling mode using the API
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You can also set the `sequential_deployment` option when deploying an
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application through the API:
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```
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POST /api/app/v1/service/ HTTP/1.1
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{
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"sequential_deployment": true,
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[...]
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}
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```
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See [create a new service](/apidocs/docker-cloud.md#create-a-new-service) for
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more information.
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### Set the scaling mode using the CLI
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You can also set the `sequential_deployment` option when deploying an
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application through the CLI:
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```bash
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$ docker-cloud service run --sequential [...]
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```
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