Backends

The backends concepts provide a representation of data, metadata and other files that either reside on a local or remote storage.

The backends have a static representation in the database (i.e the data models) and a dynamic behavioral implementation: the handlers. The combintation of both allows the registration of storages, backend authorization and data items and the access at runtime.

Data model

The backends data model are represented by Django database models. The following classes provide both concrete and abstract model for the use of the other components of EOxServer.

Data Item

This abstract model is used to reference files, which are either local, or residing on a Storage Model. Each concrete implementation of this abstract class has at least a reference to a Storage, a location and an optional format specifier.

The location is always relative to the specified storage. When no storage is set, it is treated as a path to a local file.

Examples of concrete data items are the ArrayDataItem to store raster data for Coverages or the MetaDataItem to store arbitrary metadata for geospatial objects.

Storage

The Storage model allows to provide a simple abstraction of files on a remote storage or a local archive file. The type of the storage is denoted by its storage_type field. This value is used when accessing the storage via the StorageHandler class of the appropriate type.

Each storage has a url field that provides a basic “location” of the storage. The meaning of the field depends on the storage type. For an HTTP storage, for example, the URL would be the URL to the HTTP server and the root path for all data items to use, whereas for a ZIP file storage the URL is the path to the ZIP file.

Each storage can be given a name, which helps with management.

A Storage can be linked to a Storage Auth model, which allows to specify authorization credentials.

Default storage handlers

Storage type

Description

ZIP

ZIP file storage.

TAR

TAR file storage

directory

A local directory is treated as a storage file storage

HTTP

An HTTP server storage.

FTP

An FTP server storage.

swift

OpenStack swift object storage.

Storage Auth

The StorageAuth model stores authorization credentials. Similarly to the Storage Model it is linked to a storage authorization handler class via its storage_auth_type attribute. The handler actually performs the authorization with the stored credentials. A typical example is the keystone authorization used for the OpenStack Swift object storage.

Default storage auth handlers

Storage auth type

Description

keystone

Keystone client authorization. Requires the python-keystoneclient and python-swiftclient packages to be installed.

Command Line Management Interfaces

The following management commands provide facilities to manage the model instances related to the data backend.

storageauth

This command provides two subcommands to create and delete Storage Auths.

create

This sub-command allows to create a new Storage Auth. It requires the following arguments and supports the following options.

name

the name of the Storage Auth to be created for internal reference

url

the URL of the Storage Auth

--type, -t

the type of the Storage Auth

--parameter, -p

an additional parameter to set in the Storage Auth. Can be specified multiple times.

--check

check if the access to the Storage Auth actually works. Raises an error if not.

The following example shows the creation of a keystone Storage Auth. The credentials are passed in as environment variables.

python manage.py storageauth create auth-cloud-ovh "${OS_AUTH_URL_SHORT}" \
    --type keystone \
    -p auth-version "${ST_AUTH_VERSION}" \
    -p identity-api-version="${ST_AUTH_VERSION}" \
    -p username "${OS_USERNAME}" \
    -p password "${OS_PASSWORD}" \
    -p tenant-name "${OS_TENANT_NAME}" \
    -p tenant-id "${OS_TENANT_ID}" \
    -p region-name "${OS_REGION_NAME}"
delete

To delete a Storage Auth, the subcommand delete with the Storage Auth name must be passed. The following example deletes the previously created Storage Auth from above.

python manage.py storageauth delete auth-cloud-ovh
storage

This command allows to manage storages. The subcommands create, delete allow to create new storages and delete no longer required ones.

create

This sub-command creates a new storage. The following parameters and options can be passed.

name

the storages name for internal reference

url

the location reference. The actual meaning may change according to the storage type.

--type

this is the string type of the storage. See the above table Default Storage Handlers for the available ones.

--parent

if the storage type supports parent storages, this parameter can be used to specify the parent storage. This allows to nest storages, e.g a ZIP archive on a HTTP server.

--storage-auth

this parameter must be used for storage types that require additional authorization, such as OpenStack swift storages. Use the name of the Storage Auth as a value of this parameter.

The following example creates an OpenStack swift storage, linked to the Storage Auth created above.

python manage.py storage create \
    MySwiftContainer container \
    --type swift \
    --storage-auth auth-cloud-ovh
delete

This sub-command deletes a previously created storage.

name

the name of the storage to delete

python manage.py storage delete MySwiftContainer
env

This sub-command lists environment variables necessary to access the storage.

name

the name of the storage to list the environment variables for

--path

a path on the storage to list variables for

list

A sub-command to list filenames on a storage

name

the name of the storage to list files on

--pattern

a file glob pattern to filter the returned filenames

--path

a path on the storage to limit the file search