mirror of https://github.com/docker/docs.git
70 lines
3.0 KiB
Markdown
70 lines
3.0 KiB
Markdown
---
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description: Work with data volumes
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keywords: data, volumes, create, reuse
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redirect_from:
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- /docker-cloud/tutorials/download-volume-data/
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- /docker-cloud/feature-reference/volumes/
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title: Work with data volumes
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---
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In Docker Cloud, you can define one or more data volumes for a service.
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**Volumes** are directories that are stored outside of the container's
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filesystem and which hold reusable and shareable data that can persist even when
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containers are terminated. This data can be reused by the same service on
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redeployment, or shared with other services.
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## Add a data volume to a service
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Data volumes can be either specified in the image's `Dockerfile` using the
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[VOLUME instruction](/engine/reference/builder/#volume), or when
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creating a service.
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To define a data volume in a service, specify the **container path** where it
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should be created in the **Volumes** step of the **Create new service** wizard.
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Each container of the service will have its own volume. Data volumes are reused
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when the service is redeployed (data persists in this case), and deleted if the
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service is terminated.
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If you don't define a **host path**, Docker Cloud creates a new empty volume.
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Otherwise, the specified **host path** is mounted on the **container path**.
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When you specify a host path, you can also specify whether to mount the volume
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read-only, or read/write.
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## Reuse data volumes from another service
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You can reuse data volumes from another service. To do this when creating a service, go through the **Create new service**, and continue to the **Volumes** step. From the **Volumes** page, choose a source service from the **Add volumes from** menu.
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All reused data volumes are mounted on the same paths as in the source service.
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Containers must be on the same host in order to share volumes, so the containers
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of the new service will deploy to the same nodes where the source service
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containers are deployed.
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> **Note**: A service with data volumes cannot be terminated until all services that are using its volumes have also been terminated.
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## Back up data volumes
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You might find it helpful to download or back up the data from volumes that are attached to running containers.
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1. Run an SSH service that mounts the volumes of the service you want to back up.
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In the example snippet below, replace `mysql` with the actual service name.
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```
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$ docker-cloud service run -n downloader -p 22:2222 -e AUTHORIZED_KEYS="$(cat ~/.ssh/id_rsa.pub)" --volumes-from mysql tutum/ubuntu
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```
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2. Run a `scp` (secure-copy) to download the files to your local machine.
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In the example snippet below, replace `downloader-1.uuid.cont.dockerapp.io` with the container's Fully Qualified Domain Name (FQDN), and replace `/var/lib/mysql` with the path within the container from which you want to download the data. The data will be downloaded to the current local folder.
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```
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$ scp -r -P 2222 root@downloader-1.uuid.cont.dockerapp.io:/var/lib/mysql .
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```
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