deb-murano/doc/source/appdev-guide/murano_pl/class_templ.rst

Common class structure

Here is a common template for class declarations. Note, that it is in the YAML format.

Name: class name
Namespaces: namespaces specification
Extends: [list of parent classes]
Properties: properties declaration
Methods:
    methodName:
        Arguments:
            - list
            - of
            - arguments
        Body:
            - list
            - of
            - instructions

Thus MuranoPL class is a YAML dictionary with predefined key names, all keys except for Name are optional and can be omitted (but must be valid if specified).

Class name

Class names are alphanumeric names of the classes. Traditionally, all class names begin with an upper-case letter symbol and are written in PascalCasing.

In MuranoPL all class names are unique. At the same time, MuranoPL supports namespaces. So, in different namespaces you can have classes with the same name. You can specify a namespace explicitly, like ns:MyName. If you omit the namespace specification, MyName is expanded using the default namespace =:. Therefore, MyName equals =:MyName if = is a valid namespace.

Namespaces

Namespaces declaration specifies prefixes that can be used in the class body to make long class names shorter.

Namespaces:
    =: io.murano.services.windows
    srv: io.murano.services
    std: io.murano

In the example above, the srv: Something class name is automatically translated to io.murano.services.Something.

= means the current namespace, so that MyClass means io.murano.services.windows.MyClass.

If the class name contains the period (.) in its name, then it is assumed to be already fully namespace qualified and is not expanded. Thus ns.Myclass remains as is.

Note

To make class names globally unique, we recommend specifying a developer's domain name as a part of the namespace.

Extends

MuranoPL supports multiple inheritance. If present, the Extends section shows base classes that are extended. If the list consists of a single entry, then you can write it as a scalar string instead of an array. If you do not specify any parents or omit the key, then the class extends io.murano.Object. Thus, io.murano.Object is the root class for all class hierarchies.

Properties

Properties are class attributes that together with methods create public class interface. Usually, but not always, properties are the values, and reference other objects that have to be entered in an environment designer prior to a workflow invocation.

Properties have the following declaration format:

propertyName:
    Contract: property contract
    Usage: property usage
    Default: property default

Contract

Contract is a YAQL expression that says what type of the value is expected for the property as well as additional constraints imposed on a property. Using contracts you can define what value can be assigned to a property or argument. In case of invalid input data it may be automatically transformed to confirm to the contract. For example, if bool value is expected and user passes any not null value it will be converted to True. If converting is impossible exception ContractViolationException will be raised.

The following contracts are available:

Operation	Definition
$.int()	an integer value (may be null). String values consisting of digits are converted to integers
$.int().notNull()	a mandatory integer
$.string() $.string().notNull()	a string. If the value is not a string, it is converted to a string
$.bool() $.bool().notNull()	bools are true and false. 0 is converted to false, other integers to true
$.class(ns:ClassName) $.class(ns:ClassName).notNull()	value must be a reference to an instance of specified class name
$.class(ns:ClassName, ns:DefaultClassName)	create instance of the ns:DefaultClassName class if no instance provided
$.class(ns:Name).check($.p = 12)	the value must be of the ns:Name type and have the p property equal to 12
$.class(ns:Name).owned()	a current object must be direct or indirect owner of the value
$.class(ns:Name).notOwned()	the value must be owned by any object except current one
[$.int()] [$.int().notNull()]	an array of integers. Similar to other types.
[$.int().check($ > 0)]	an array of the positive integers (thus not null)
[$.int(), $.string()]	an array that has at least two elements, first is int and others are strings
[$.int(), 2] [$.int(), 2, 5]	an array of ints with at least 2 items an array of ints with at least 2 items, and maximum of 5 items
{ A: $.int(), B: [$.string()] }	the dictionary with the A key of the int type and B - an array of strings
$ [] {}	any scalar or data structure as is any array any dictionary
{ $.string().notNull(): $.int().notNull() }	dictionary string -> int
A: StringMap $.string().notNull(): $	the dictionary with the A key that must be equal to StringMap, and other keys be any scalar or data structure
$.check($ in $this.myStaticMethod())	the value must be equal to one of a member of a list returned by static method of the class
$.check($this.myStaticMethod($))	the static method of the class must return true for the value

In the example above property port must be int value greater than 0 and less than 65536; scope must be a string value and one of 'public', 'cloud', 'host' or 'internal', and protocol must be a string value and either 'TCP' or 'UDP'. When user passes some values to these properties it will be checked that values confirm to the contracts.

Namespaces:
  =: io.murano.apps.docker
  std: io.murano

Name: ApplicationPort

Properties:
  port:
    Contract: $.int().notNull().check($ > 0 and $ < 65536)

  scope:
    Contract: $.string().notNull().check($ in list(public, cloud, host, internal))
    Default: private

  protocol:
    Contract: $.string().notNull().check($ in list(TCP, UDP))
    Default: TCP

Methods:
  getRepresentation:
    Body:
      Return:
        port: $.port
        scope: $.scope
        protocol: $.protocol

Property usage

Usage states the purpose of the property. This implies who and how can access it. The following usages are available:

Value	Explanation
In	Input property. Values of such properties are obtained from a user and cannot be modified in MuranoPL workflows. This is the default value for the Usage key.
Out	A value is obtained from executing MuranoPL workflow and cannot be modified by a user.
InOut	A value can be modified both by user and by workflow.
Const	The same as In but once workflow is executed a property cannot be changed neither by a user nor by a workflow.
Runtime	A property is visible only from within workflows. It is neither read from input nor serialized to a workflow output.
Static	Property is defined on a class rather than on an instance. See static_methods_and_properties for details.
Config	A property allows to have per-class configuration. A value is obtained from the config file rather than from the object model. These config files are stored in a special folder that is configured in the [engine] section of the Murano config file under the class_configs key.

The usage attribute is optional and can be omitted (which implies In).

If the workflow tries to write to a property that is not declared with one of the types above, it is considered to be private and accessible only to that class (and not serialized to output and thus would be lost upon the next deployment). An attempt to read the property that was not initialized results in an exception.

Default

Default is a value that is used if the property value is not mentioned in the input object model, but not when it is set to null. Default, if specified, must conform to a declared property contract. If Default is not specified, then null is the default.

For properties that are references to other classes, Default can modify a default value of the referenced objects. For example:

p:
 Contract: $.class(MyClass)
 Default: {a: 12}

This overrides default for the a property of MyClass for instance of MyClass that is created for this property.

Workflow

Workflows are the methods that describe how the entities that are represented by MuranoPL classes are deployed.

In a typical scenario, the root object in an input data model is of the io.murano.Environment type, and has the deploy method. This method invocation causes a series of infrastructure activities (typically, a Heat stack modification) and the deployment scripts execution initiated by VM agents commands. The role of the workflow is to map data from the input object model, or a result of previously executed actions, to the parameters of these activities and to initiate these activities in a correct order.

Methods

Methods have input parameters, and can return a value to a caller. Methods are defined in the Workflow section of the class using the following template:

methodName:
    Scope: Public
    Arguments:
       - list
       - of
       - arguments
    Body:
       - list
       - of
       - instructions

Public is an optional parameter that specifies methods to be executed by direct triggering after deployment.

Method arguments

Arguments are optional too, and are declared using the same syntax as class properties. Same as properties, arguments also have contracts and optional defaults.

Unlike class properties Arguments may have a different set of Usages:

Value	Explanation
Standard	Regular method argument. Holds a single value based on its contract. This is the default value for the Usage key.
VarArgs	A variable length argument. Method body sees it as a list of values, each matching a contract of the argument.
KwArgs	A keywrod-based argument, Method body sees it as a dict of values, with keys being valid keyword strings and values matching a contract of the argument.

Arguments example:

scaleRc:
  Arguments:
    - rcName:
        Contract: $.string().notNull()
    - newSize:
        Contract: $.int().notNull()
    - rest:
        Contract: $.int()
        Usage: VarArgs
    - others:
        Contract: $.int()
        Usage: KwArgs

Method body

The Method body is an array of instructions that get executed sequentially. There are 3 types of instructions that can be found in a workflow body:

• Expressions,
• Assignments,
• Block constructs.

Method usage

Usage states the purpose of the method. This implies who and how can access it. The following usages are available:

Value	Explanation
Runtime	Normal instance method.
Static	Static method that does not require class instance. See static_methods_and_properties for details.
Extension	Extension static method that extends some other type. See extension_methods for details.
Action	Method can be invoked from outside (using Murano API). This option is deprecated for the package format versions > 1.3 in favor of Scope: Public and occasionally will be no longer supported. See actions for details.

The Usage attribute is optional and can be omitted (which implies Runtime).

Method scope

The Scope attribute declares method visibility. It can have two possible values:

• Session - regular method that is accessible from anywhere in the current execution session. This is the default if the attribute is omitted;
• Public - accessible anywhere, both within the session and from outside through the API call.

The Scope attribute is optional and can be omitted (which implies Session).

Expressions

Expressions are YAQL expressions that are executed for their side effect. All accessible object methods can be called in the expression using the $obj.methodName(arguments) syntax.

Expression	Explanation
$.methodName() $this.methodName()	invoke method 'methodName' on this (self) object
$.property.methodName() $this.property.methodName()	invocation of method on object that is in property
$.method(1, 2, 3)	methods can have arguments
$.method(1, 2, thirdParameter => 3)	named parameters also supported
list($.foo().bar($this.property), $p)	complex expressions can be constructed

Assignment

Assignments are single key dictionaries with a YAQL expression as a key and arbitrary structure as a value. Such a construct is evaluated as an assignment.

Assignment	Explanation
$x: value	assigns value to the local variable $x
$.x: value $this.x: value	assign value to the object's property
$.x: $.y	copies the value of the property y to the property x
$x: [$a, $b]	sets $x to the array of two values: $a and $b
$x:   SomeKey:     NestedKey: $variable	structures of any level of complexity can be evaluated
$.x[0]: value	assigns value to the first array entry of the x property
$.x: $.x.append(value)	appends value to the array in the x property
$.x: $.x.insert(1, value)	inserts value into position 1 of the array in the x property
$x: list($a, $b).delete(0)	sets $x to the list without the item at index 0
$.x.key.subKey: value $.x[key][subKey]: value	deep dictionary modification

Block constructs

Block constructs control a program flow. They are dictionaries that have strings as all their keys.

The following block constructs are available:

Assignment	Explanation
Return: value	Returns value from a method
If: predicate() Then:   - code   - block Else:   - code   - block	predicate() is a YAQL expression that must be evaluated to True or False The Else section is optional One-line code blocks can be written as scalars rather than an array.
While: predicate() Do:   - code   - block	predicate() must be evaluated to True or False
For: variableName In: collection Do:   - code   - block	collection must be a YAQL expression returning iterable collection or evaluatable array as in assignment instructions, for example, [1, 2, $x] Inside a code block loop, a variable is accessible as $variableName
Repeat: Do:   - code   - block	Repeats the code block specified number of times
Break:	Breaks from loop
Match:   case1:     - code     - block   case2:     - code     - block Value: $valExpression() Default:   - code   - block	Matches the result of $valExpression() against a set of possible values (cases). The code block of first matched case is executed. If no case matched and the default key is present than the Default code block get executed. The case values are constant values (not expressions).
Switch:   $predicate1():     - code     - block   $predicate2():     - code     - block Default:   - code   - block	All code blocks that have their predicate evaluated to True are executed, but the order of predicate evaluation is not fixed. The Default key is optional. If no predicate evaluated to True, the Default code block get executed.
Parallel:   - code   - block Limit: 5	Executes all instructions in code block in a separate green threads in parallel. The limit is optional and means the maximum number of concurrent green threads.
Try:   - code   - block Catch: With: keyError As: e Do:   - code   - block Else:   - code   - block Finally:   - code   - block	Try and Catch are keywords that represent the handling of exceptions due to data or coding errors during program execution. A Try block is the block of code in which exceptions occur. A Catch block is the block of code, that is executed if an exception occurred. Exceptions are not declared in Murano PL. It means that exceptions of any types can be handled and generated. Generating of exception can be done with construct: Throw: keyError. The Else is optional block. Else block is executed if no exception occurred. The Finally also is optional. It's a place to put any code that will be executed, whether the try-block raised an exception or not.

Notice, that if you have more then one block construct in your workflow, you need to insert dashes before each construct. For example:

Body:
  - If: predicate1()
    Then:
      - code
      - block
  - While: predicate2()
    Do:
      - code
      - block

Object model

Object model is a JSON serialized representation of objects and their properties. Everything you do in the OpenStack dashboard is reflected in an object model. The object model is sent to the Application catalog engine when the user decides to deploy the built environment. On the engine side, MuranoPL objects are constructed and initialized from the received Object model, and a predefined method is executed on the root object.

Objects are serialized to JSON using the following template:

{
    "?": {
        "id": "globally unique object ID (UUID)",
        "type": "fully namespace-qualified class name",

        "optional designer-related entries can be placed here": {
            "key": "value"
        }
    },

    "classProperty1": "propertyValue",
    "classProperty2": 123,
    "classProperty3": ["value1", "value2"],

    "reference1": {
        "?": {
            "id": "object id",
            "type": "object type"
        },

        "property": "value"
    },

    "reference2": "referenced object id"
}

Objects can be identified as dictionaries that contain the ? entry. All system fields are hidden in that entry.

There are two ways to specify references:

1. reference1 as in the example above. This method allows inline definition of an object. When the instance of the referenced object is created, an outer object becomes its parent/owner that is responsible for the object. The object itself may require that its parent (direct or indirect) be of a specified type, like all applications require to have Environment somewhere in a parent chain.
2. Referring to an object by specifying other object ID. That object must be defined elsewhere in an object tree. Object references distinguished from strings having the same value by evaluating property contracts. The former case would have $.class(Name) while the later - the $.string() contract.