Specify Volume Datastores

Volume stores for virtual container hosts (VCHs) are storage locations in your infrastructure, in which to create volumes when container developers use the docker volume create command or deploy containers that use volumes. You can specify a mix of volume stores backed by vSphere datastores or NFSv3 shares. The volume stores that are available to a VCH appear under VolumeStores when you run docker info against the VCH.

About Volume Stores

For information about how Docker containers use volumes, see Use volumes in the Docker documentation.

To specify a volume store, you provide the datastore name or NFS mount point, an optional path to a specific folder in that datastore, and a volume store label.

The label that you specify is the volume store name that Docker uses. For example, the volume store label appears in the information for a VCH when container developers run docker info. Container developers specify the volume store label in the docker volume create --opt VolumeStore=volume_store_label option when they create a volume. The volume store label must be unique.

You can create multiple volume stores for a single VCH.

IMPORTANT: If you do not specify a volume store when you create a VCH, no volume store is created by default and container developers cannot create or run containers that use volumes. You can add volume stores to a VCH after deployment by running vic-machine configure --volume-store. For information about adding volume stores after deployment, see Add Volume Stores.

If you delete a VCH, by default any volumes that the VCH manages remain available in the volume store. There are different ways to delete volumes that are no longer required:

  • Delete the volumes manually in the vSphere Client.
  • Run docker rm -v.
  • Run vic-machine delete with the --force option.
  • Select Delete persistent and anonymous volumes when you delete the VCH in the vSphere Client.

vSphere Datastores

If you are deploying the VCH to a vCenter Server cluster, the vSphere datastores that you designate as volume stores should be shared by at least two, but preferably all, ESXi hosts in the cluster. Using non-shared datastores is possible and deployment succeeds, but results in a warning that this configuration limits the use of vSphere features such as vSphere vMotion and DRS.

If you specify a vSphere datastore without specifying a datastore folder, vSphere Integrated Containers Engine creates a folder named VIC/volumes at the top level of the target datastore. Any volumes that container developers create will appear in the VIC/volumes folder.

If you specify a vSphere datastore and a datastore folder, vSphere Integrated Containers Engine creates a folder named volumes in the location that you specify. If the folders that you specify do not already exist on the datastore, vSphere Integrated Containers Engine creates the appropriate folder structure. Any volumes that container developers create will appear in the path/volumes folder.

vSphere Integrated Containers Engine creates the volumes folder independently from the folders for VCH files so that you can attach existing volume stores to different VCHs. You can assign an existing volume store that already contains data to a VCH by either creating a new VCH or by running vic-machine configure --volume-store on an existing one. You can only assign a volume store to a single VCH at a time.

IMPORTANT: If multiple VCHs use the same datastore for their volume stores, specify a different datastore folder for each VCH. Do not designate the same datastore folder as the volume store for multiple VCHs.

NFS Volume Stores

If you use NFS volume stores, concurrently running containers can share the volumes from those stores, whereas volumes on vSphere datastores cannot be shared by concurrently running containers. For example, you can use shared NFS volume stores to share configuration information between running containers, or to allow running containers to access the data of another container. Another use case for NFS volume stores is a build system, in which you might have multiple identical containers that are potentially running parallel tasks, and you want to store their output in a single place.

To use shared NFS volume stores, it is recommended that the NFS share points that you designate as the volume stores be directly accessible by the network that you use as the container network. For information about container networks, see the description of the --container-network option.

IMPORTANT:

  • NFS volume stores do not support FQDN. When using FQDN to identify NFS shares, it is not possible to set a DNS-Search-List. Container VMs fail to start, with the error docker: Error response from daemon: Server error from portlayer: unable to wait for process launch status: container VM has unexpectedly powered off. Always use IP addresses for NFS shares.
  • When container developers run docker info or docker volume ls against a VCH, there is currently no indication whether a volume store is backed by vSphere or by an NFS share point. Consequently, you should include an indication that a volume store is an NFS share point in the volume store label.
  • You cannot specify the root folder of an NFS server as a volume store.

About NFS Volume Stores and Permissions

vSphere Integrated Containers mounts NFS volumes as root. Consequently, if containers are to run as non-root users, the volume store must be configured with the correct permissions so that the non-root users can access it.

Permissions are determined by the NFS server. If a container runs as non-root and it attempts to write into the NFS mount, the permissions on the server side must grant the accessing user the ability to perform the requested actions. To allow this, the other (also known as world) permissions must be set. Alternatively, the user that is accessing the NFS mount should be part of the same Group that owns the share. To facilitate this, you can configure the share point with an anonymous user. You can also use root_squash, which is designed to map the root user to the anonymous user. Using all squash maps all UIDs/GIDs to the anonymous UID/GID.

In this case, you must configure the volume store with a UID/GID for creation and reading. This is because there will be many containers potentially attempting to read or write to the same location. You make this configuration on the NFS server. The configuration of the sharepoint is dependent on your setup:

  • If squash_root is enabled, the anon user or group must have permissions on the NFS sharepoint. This is the preferred option for production environments.
  • If no_squash_root is enabled, the root user or group needs permissions on the NFS sharepoint. This option is acceptable and works, but is recommended for proof-of-concept deployments rather than production.
  • The root user must also be a member of the GID that you configure the VCH to use.

If you encounter connection difficulties, and you are not sure whether the squash is the problem, you can enable all_squash on the sharepoint and configure the anon user as the owner of the endpoint.

Testing and Debugging NFS Volume Store Configuration

When you deploy a VCH, if you configured an NFS volume store and the NFS share point is not accessible by the VCH, the following errors appear in the output of vic-machine create:

DEBU[0269] Portlayer has established volume stores (default others)
ERRO[0269] VolumeStore (shared) cannot be brought online - check network, nfs server, and --volume-store configurations
ERRO[0269] Not all configured volume stores are online - check port layer log via vicadmin

More detailed information about the NFS share point appears in the Port Layer Service logs, that you can access by using the VCH Administration Portal for the VCH:

INFO  op=363.7: Creating nfs volumestore shared on nfs://nfs_server/not-there
DEBUG op=363.7: Mounting nfs://nfs_server/not-there
Failed to connect to portmapper: dial tcp nfs_server:111: getsockopt: connection refused
ERROR op=363.7: error occurred while attempting to mount volumestore (shared). err: (dial tcp nfs_server:111: getsockopt: connection refused)
ERROR op=363.7: dial tcp nfs_server:111: getsockopt: connection refused

NOTE: The DEBUG line in the example above is only included if you run the VCH with a debug setting of 1 or greater.

After you deploy a VCH, you can test that an NFS share point is configured correctly so that containers can access it by running the following commands:

docker volume create --name test --opt VolumeStore=nfs
docker run -it test:/mnt/test alpine /bin/ash

You can also test the configuration mounting the NFS share point directly in the VCH endpoint VM. For information about how to perform this test, see Install Packages in the Virtual Container Host Endpoint VM and Mount an NFS Share Point in the VCH Endpoint VM.

Another option is to start a container that has an NFS client and attempt to mount the NFS share point in that container. This is a good option for VCH users that do not have access to vic-machine and cannot log in to the VCH by using SSH. This is also a good way to test access to NFS volume stores through firewalls and for VCHs that implement container networks. Containers connect to NFS volume stores over the network stack of the container VM, so the containers must be able to connect to the NFS server.

Anonymous Volumes

If you only require one volume store, set the volume store label to default. If you set the volume store label to default, container developers do not need to specify the --opt VolumeStore=volume_store_label option when they run docker volume create. Also, some common container images require the presence of a default volume store in order to run.

IMPORTANT: If container developers intend to create containers that are attached to anonymous or named volumes by using docker create -v , you must create a volume store with a label of default.

Add Volume Datastores

This section describes the Volume Datastores section of the Storage Capacity page of the Create Virtual Container Host wizard, and the corresponding vic-machine create option.

Create VCH Wizard

  1. Optionally enable anonymous volumes by setting the Enable anonymous volumes switch to the green ON position.

    Enabling anonymous volumes automatically adds the label default to the first volume datastore.

  2. Select a datastore for the first volume store from the Datastore drop-down menu.

  3. In the Folder text box, optionally enter the path to a folder in the specified datastore.

    If the folders that you specify in the path do not already exist on the selected datastore, vSphere Integrated Containers Engine creates the appropriate folder structure.

  4. If you did not enable anonymous volumes, or if this is an additional volume store, provide a label for the volume store in the Volume store name text box.
  5. Optionally click the + button to add more volume datastores to the VCH, and repeat the proceeding steps for each additional volume datastore.

NOTE: It is not currently possible to specify an NFS share point as a volume store in the Create Virtual Container Host wizard. If you use the wizard to create VCHs, after deployment, run vic-machine configure with the --volume-store option to add NFS share points to the VCH. For information about adding volume stores after deployment, see Add Volume Stores.

vic-machine Option

--volume-store, --vs

To specify a whole vSphere datastore for use as a volume store, provide the datastore name and a volume store label:

--volume-store datastore_name:volume_store_label

Optionally use the ds:// prefix to specify a datastore that is backed by vSphere:

--volume-store ds://datastore_name:volume_store_label

To specify a volume store in a datastore folder, add the path to the appropriate folder:

--volume-store datastore_name/datastore_path:volume_store_label

To specify an NFS share point as a volume store, use the nfs:// prefix and the path to an NFS server and a shared mount point:

nfs://nfs_server/path_to_share_point:nfs_volume_store_label

You can also specify the URL, UID, and GID of a shared NFS mount point when you specify an NFS share point. Connections are made over TCP. If you do not specify a UID and GID, vSphere Integrated Containers Engine uses the anon UID and GID when creating and interacting with the volume store. The anon UID and GID is 1000:1000.

--volume-store nfs://nfs_server/path_to_share_point?uid=1234&gid=5678:nfs_volume_store_label

NOTES:

  • If your NFS server uses a different anon UID/GID to the default, you must specify the UID/GID in the --volume-store option. Configuring a VCH to use a different default anon UID/GID for NFS volume stores is not supported. For containers, the user that is running the process in the container needs to have the correct permissions on the mount to read and write.
  • vSphere Integrated Containers mounts NFS volumes as root. Consequently, if you specify a UID/GID, it must be valid for root. Additionally, if containers are to run as non-root users, the export of the volume must grant the correct permissions to the non-root users so that they can access the volume store.
  • For more information about the preceding points, see About NFS Volume Stores and Permissions above.

Use the label default to allow container developers to create anonymous volumes:

--volume-store ds://datastore_name:default
--volume-store nfs://nfs_server/path_to_share_point:default

You can specify the --volume-store option multiple times, and add a mixture of vSphere datastores and NFS share points to a VCH:

--volume-store datastore_name/path:volume_store_label_1
--volume-store datastore_name/path:volume_store_label_2
--volume-store nfs://nfs_server/path_to_share_point:nfs_volume_store_label

If you specify an invalid vSphere datastore name or an invalid NFS share point URL, vic-machine create fails and suggests valid datastores.

What to Do Next

If you are using the Create Virtual Container Host wizard, click Next to go to the VCH Networks settings.

Example vic-machine Commmand

This example vic-machine create command deploys a VCH with 3 volume stores:

  • A default volume store in the volumes folder on datastore 1.
  • A second volume store named volume_store_2 in the volumes folder on datastore 2.
  • A volume store named shared_volume in a NFS share point, from which containers can mount shared volumes.
vic-machine-operating_system create
--target 'Administrator@vsphere.local':password@vcenter_server_address/dc1
--compute-resource cluster1
--bridge-network vch1-bridge
--public-network vic-public
--image-store 'datastore 1'
--volume-store 'datastore 1'/volumes:default
--volume-store 'datastore 2'/volumes:volume_store_2
--volume-store nfs://nfs_server/path/to/share/point:shared_volume
--name vch1
--thumbprint certificate_thumbprint
--no-tlsverify

Troubleshooting

VCHs require datastores to be writable. For information about how to check whether a shared NFS datastore is possibly mounted as read-only, see VCH Deployment with a Shared NFS Datastore Fails with an Error About No Single Host Being Able to Access All Datastores.

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