OVF packages are ideal for distributing complex software packages. As we saw in the post on
"Inside the OVF Package",
it is possible to tailor the same OVF package for different hypervisors
using deployment options. Moreover, it is possible to add meaningful
human readable descriptions to the different parts of the OVF
descriptor, in places like product information, EULA sections and
deployment options. This enables deployment wizards (like the vSphere
client) to give the user a great experience when deploying an OVF
package, since it can use specific messages relevant to a particular
OVF descriptor. For example, the user can see messages about the
intention of deployment options and properties, and how to use them.
This blog post is about what to do about all that human readable
metadata, when you want to distribute your OVF package in different
countries and for different languages.
The OVF specification includes an internationalization section that
describes how to localize an OVF descriptor. This lets you address the
issue of translating all the human readable metadata in the OVF
descriptor without having to keep multiple copies of the descriptor,
each localized to a specific language. Obviously it does not make sense
to localize everything in an OVF descriptor, since some information is only
intended to be read by a machine. A rule of thumb is that you can localize all the elements that carry some kind of metadata which
are useful to the deployer of the OVF package but not needed by the
deployment platform. For a full list of elements that can be localized
please see the list at the end of this blog post.
Example
Let us take a look at how the user experiences an OVF package that has been localized:
OVF deployment using default language.
OVF deployment using German localization.
The vSphere Client attempts to use the localized messages from the OVF
package which matches the locale of the users Windows installation. If
a matching localization is not found, the default language of the OVF
descriptor (English in the example) is used.
Localizing the OVF Descriptor
Let’s look at how to write an OVF descriptor that is localized to
multiple language including both English and German as in the above
example, but also Danish and Swahili:
<Envelope xml:lang="en-US">
...
<VirtualSystem ovf:id="MyVM">
...
<ProductSection>
<Info>Information about the installed software</Info>
<Property ovf:key="num_connections" ovf:type="string"
ovf:userConfigurable="true">
<Label ovf:msgid="num_connections.label">
Number of connections
</Label>
</Property>
<Property ovf:key="admin_address" ovf:type="string"
ovf:userConfigurable="true">
<Label ovf:msgid="admin_address.label">Administrator address</Label>
<Description ovf:msgid="admin_address.description">
Email address of the systems administrator
</Description>
</Property>
</ProductSection>
...
</VirtualSystem>
<!-- German localized messages -->
<Strings xml:lang="de-DE">
<Msg ovf:msgid="num_connections.label">Zahl der Anschlüsse</Msg>
<Msg ovf:msgid="admin_address.label">Verwalteradresse</Msg>
<Msg ovf:msgid="admin_address.description">
Email address des Systemverwalters
</Msg>
</Strings>
<!-- Danish localized messages -->
<Strings xml:lang="da-DK">
<Msg ovf:msgid="num_connections.label">Antal forbindelser</Msg>
<Msg ovf:msgid="admin_address.label">Administrator adresse</Msg>
<Msg ovf:msgid="admin_address.description">
System administratorens email-adresse
</Msg>
</Strings>
<!-- Swahili localized messages -->
<Strings xml:lang="sw">
<Msg ovf:msgid="num_connections.label">Idadi ya connections</Msg>
<Msg ovf:msgid="admin_address.label">Administrator anwani</Msg>
<Msg ovf:msgid="admin_address.description">
Barua pepe ya system administrator
</Msg>
</Strings>
</Envelope>
In this example, we are localizing the label of the "num_connections" property and the label and description of the "admin_address" property.
As you can see, it is pretty straight forward to localize an OVF descriptor to support multiple languages:
- First prepare the OVF descriptor for localization by adding an
ovf:msgid attribute to each of the elements you want to be localized
(see the list of possible elements in the last section of this blog entry)
and give the ovf:msgid a unique value;
- Next you add a Strings section for each of the locales you
want to support and specify the locale by using the xml:lang attribute;
- For each ovf:msgid attribute in the OVF descriptor create a Msg element in the Strings section with the same ovf:msgid value.
The human readable messages in the example ProductSection element
are used as the default language and will be used if no appropriate
locale is available in the descriptor. To specify the default language
of the OVF descriptor (the language used in the default messages), set
the xml:lang attribute on the top Envelope element level. In our
example we have set it to US English (en-US).
The format of the locale is standard and is written as
[language]-[country]-[variant]. It is not necessary to specify the full
locale for a string bundle. For example, if we simply specify the
German locale in the example as de it can then be used for several
German speaking countries such as Austria (de-AT), Germany (de-DE),
Luxembourg (de-LU) and parts of Switzerland (de-CH). If a user uses locale X on his computer, we select the locale in the OVF descriptor
which matches the beginning or all of X. If two locales match X we
chose the one that gives the longest match. This is why changing the
locale from de-DE to de means that the localization can be used on the
locales de-AT, de-DE, de-LU and de-CH, since de is a prefix of those.
External String Bundles
Often when managing multiple locales it is impractical to keep
them in the same file. For this purpose the OVF specification allows
you to extract all the Strings elements and put them in separate files.
From the example OVF descriptor we have used, we can take all the three
different localizations and put them in separate files (we will call these
files string bundles):
<Envelope> <References> <File ovf:href="MyVM-de-DE.msg" ovf:id="msgs1"/> <File ovf:href="MyVM-da-dk.msg" ovf:id="msgs2"/> <File ovf:href="MyVM-sw.msg" ovf:id="msgs3"/> <File ovf:href="MyVM-disk1.vmdk" ovf:id="file2" ovf:size="9580544"/> ... </References> ...</Envelope>The files are then referenced in the beginning of the Reference section
in the OVF descriptor (important: String bundles must be listed first
in the reference section):
File: MyVM-de-DE.msg
<!-- German localized messages -->
<Strings xml:lang="de-DE">
<Msg ovf:msgid="num_connections.label">Zahl der Anschlüsse</Msg>
<Msg ovf:msgid="admin_address.label">Verwalteradresse</Msg>
<Msg ovf:msgid="admin_address.description">
Email address des Systemverwalters
</Msg>
</Strings>
File: MyVM-da-DK.msg
<!-- Danish localized messages -->
<Strings xml:lang="da-DK">
<Msg ovf:msgid="num_connections.label">Antal forbindelser</Msg>
<Msg ovf:msgid="admin_address.label">Administrator adresse</Msg>
<Msg ovf:msgid="admin_address.description">
System administratorens email-adresse
</Msg>
</Strings>
File: MyVM-sw.msg
<!-- Swahili localized messages -->
<Strings xml:lang="sw">
<Msg ovf:msgid="num_connections.label">Idadi ya connections</Msg>
<Msg ovf:msgid="admin_address.label">Administrator anwani</Msg>
<Msg ovf:msgid="admin_address.description">
Barua pepe ya system administrator
</Msg>
</Strings>
In the above example we created three files, one for each locale. The OVF
specification allows multiple Strings elements in the same file next to
the OVF descriptor, so it is not necessary to create a file per locale
as we did. However, by keeping the locales in separate
string bundles it become easy to extend the supported locales simply by
adding more string bundle files.
Further Reading
To learn more about localization, check out section in the OVF 1.0.0 specification: http://www.dmtf.org/standards/published_documents/DSP0243_1.0.0.pdf.
List of Localizable Elements
The text in the following elements can be localized:
- Info element on VirtualSystem and VirtualSystemCollection
- Name element on VirtualSystem and VirtualSystemCollection
- Info element on AnnotationSection, DeploymentOptionSection,
DiskSection, EulaSection, InstallSection, NetworkSection,
OperatingSystemSection, ProductSection, ResourceAllocationSection,
StartupSection and VirtualHardwareSection.
- Annotation element on AnnotationSection
- License element on EulaSection
- Description element on NetworkSection
- Description element on OperatingSystemSection
- Description, Product, Vendor, Label, and Category elements on ProductSection
- Description and Label elements on DeploymentOptionSection
- ElementName, Caption and Description sub-elements on the System element in VirtualHardwareSection
- ElementName, Caption and Description sub-elements on Item elements in VirtualHardwareSection
- ElementName, Caption and Description sub-elements on Item elements in ResourceAllocationSection
