DC 6.0 Configuration Management: Digizuite configuration language

Owned by Rasmus Hjelmberg Duemose Hansen
May 13, 2024
6 min read

As mentioned in the previous documentation of Configuration management, the State is defined in a set of Configuration layers which in turn is a text file which described configuration by declaration.

The text language in which configuration is defined is called Digizuite configuration language (DCL).

The language

The language is a simple declarative language in which you can define the desired configuration. Below is a descriptions of the concepts.

Resources

A resource is the most basic thing in config management. Each resource entry corresponds to a single configuration in the Digizuite. It can be any configuration like a metafield, a user, or simply a single node in a tree metafield.

A resource has many properties, some that can be set as part of configuring the resource, and some that only exist after the resource has been created. This could for instance be an identifier that is generated on creation and used from other resources to easily link related resources together.

A resource can be created, updated, and deleted by the config management system. This allows the management of resources consistently between environments.

Resources use the following syntax in the DCL:

resource metafield my_field { name = "My Field" }

Variables

A variable is a special kind of value, where the value itself is not defined as part of the configuration but is provided from an external system. This could be things like keys for Azure blob storage, which is something that needs to be different between environments, but where the underlying purpose of having a "blob storage" is the same.

Variables use the following syntax in the DCL:

variable my_variable { type = "string" }

 

The system will throw you an error if you do not have the variable in use in any resource.

Variables have to be used in the layer they are defined in. If you want to use a variable in multiple layers, you will have to add an identical variable to the other layer it should be used in. This will make the variable only show up once in the variable editor.

 

You may choose to define a default value. A string field with a default would appear as such:

variable my_variable { type = "string" default = 'Some default text' }

If you have the same variable key in multiple layers, you do have the option to have the defaults be different (if you define one, you have to define all others). It will appear as such in the variable editor.

Locals

Locals a temporary values that are used internally to allow easily reusing certain values without repeating them over and over.

Locals use the following syntax in the DCL:

Layers

To achieve to ability to provide configurations that can be changed and updated independently the config management system provides something called "layers". Each layer is a separately provided configuration. For example the bottom most layer is likely the basic DAM configuration that is required for the DAM to even be able to start. The next layer up might be the Media Manager layer, which provides all the metafields, labels and other configuration Media Manager needs to start.

Layers can generally be separated into two categories, predefined layers, like the DAM and Media Manager layer mentioned above, and customized layers like what each customer would do. The predefined layers are not editable by the customer, while the custom layers are.

Data references

To access something on a previous layer you need to use a data reference. Data references looks like normal resources, but rather than creating a resource that matches the specified description, it checks all previous layers for a unique resource that looks like that specified definition. Once you have a data reference, you can either use the properties when creating new resource, or use the patch functionality to modify the resource.

Data references use the following syntax in the DCL:

Patches

To change a resource in a previous layer patches can be used. A patch takes a target to update, and the new values the properties should have. It is only necessary to specify the properties that should actually change in the patch definition.

The target for a patch is always a data reference. If resource is defined in the same layer, you can just go edit it directly, and then you do not need a patch.

The syntax for patches are as follows:

The Digizuite Configuration Language (DCL)

The DCL consists of several individual parts that are brought together to allow for huge flexibility. The language is heavily inspired by HCL from Hashicorp: https://www.terraform.io/docs/language/syntax/configuration.html .

The major building blocks will be shown in this section, and then we will finish with an example of how to attach these things together.

DCL types

The first thing you need to know about the language are the available primitive types:

  • String "foo", is a string with the value foo. Strings are easy to recognize from the quotes around the value. Both single quote and multi quote strings are allowed, and support the exact same functionality.

  • Int 42, is an int with the value 42. Ints can be recognized because they are numbers without quotes.

  • Decimal 3.14, is a decimal with the value 3.14. DCL makes no distinction between float and double types.

  • Boolean true or false, are booleans with either the value true or the value false.

Next are the composite types:

  • Object, which is a collection of key-value pairs, where each value is one of the types described in this section. Keys are always strings, but without the quotes.

  • Array, which is an array of values of objects.

Example

A full example of using all these types can look like this:

Object also accepts the following shorthand syntax, where the = character is omitted:

Functions

DCL allows calling predefined functions to do things that are not directly available in the syntax.

A function call looks like this:

This calls a function called my_function and passes in the arguments "my first argument" and "my second argument" as the first and second arguments respectively.

Any of the types described in the "DCL Types" section can be passed as arguments to functions.

A set of functions are available out of the box. It is not possible to define custom functions.

The available functions are as follows

  • file(<Relative path to file in the configuration file structure>) - function that can be used to refer to binary files

  • text_file(<Relative path to file in the configuration file structure>) - function that allows the user to have e.g. workflow definitions in separate files in a configuration layer

Both function input and outputs are strongly typed, and will be validated.

References

To make it easier to reuse parts between resources and link resources, DCL has a concept of references. References are a way of using a property of one resource in another resource.

In the simplest form it looks like this:

In the above example the group_id property is set to the same value as the id property of the "Asset Info" meta group. Accessing nested properties is also possible using additional .s to dig into the object.

It is possible to use properties that are not known at compile time. Because of this the config management engine is smart enough to create resources in the correct order. In the above case the meta_group, asset_info, would be created before the title metafield. In the same, but opposite direction, if there are no references, direct or indirect between two resources, they are freely be created in parallel.

References can also be passed as arguments to function, in which case the functions will only be called after the referenced properties are available.

String interpolation

All string types support string interpolation, which looks like this:

String interpolation allows the user to combine multiple values, and make then dependent on each other.