Common class structure¶
Here is a common template for class declarations. Note, that it is in the YAML format.
1Name: class name
2Namespaces: namespaces specification
3Extends: [list of parent classes]
4Properties: properties declaration
5Methods:
6 methodName:
7 Arguments:
8 - list
9 - of
10 - arguments
11 Body:
12 - list
13 - of
14 - 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
|
$.template(ns:ClassName)
$.template(ns:ClassName).notNull()
|
value must be a dictionary with object-model representation 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 beany 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 below 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
The template
contract does the same validation as the class
contract,
but does not require the actual object to be passed as a property or argument.
Instead it allows to create an object from the given template later. Also you
can exclude some of the properties from validation and provide them later in
the body of the method.
Consider the following example:
Namespaces:
=: io.murano.applications
res: io.murano.resources
std: io.murano
Name: TemplateServerProvider
Properties:
template:
Contract: $.template(res:Instance, excludeProperties => [name]).notNull()
serverNamePattern:
Contract: $.string().notNull()
threshold:
Contract: $.int().check($ > 0)
Methods:
createReplica:
Arguments:
- index:
Contract: $.int().notNull()
- owner:
Contract: $.class(std:Object)
Body:
- If: $index < $this.threshold
Then:
- $template: $this.template
- $template.name: $this.serverNamePattern.format($index)
- $template['?'].name: format('Server {0}', $index)
- Return: new($template, $owner)
Else:
- Return: null
In the example above the class has the template
property that is validated
by the template
contract. It holds the template of the object of the
Instance
class or its inheritor. In the createReplica
method
template
is used to dynamically create instances in runtime considering
some conditions and customizing the name
property of an instance, as it
was excluded from validation.
You still can pass an actual object to the property or argument with the
template
contract, but it will be automatically converted to its object
model representation.
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 Murano 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 optionalOne-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 than 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:
1{
2 "?": {
3 "id": "globally unique object ID (UUID)",
4 "type": "fully namespace-qualified class name",
5
6 "optional designer-related entries can be placed here": {
7 "key": "value"
8 }
9 },
10
11 "classProperty1": "propertyValue",
12 "classProperty2": 123,
13 "classProperty3": ["value1", "value2"],
14
15 "reference1": {
16 "?": {
17 "id": "object id",
18 "type": "object type"
19 },
20
21 "property": "value"
22 },
23
24 "reference2": "referenced object id"
25}
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:
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 haveEnvironment
somewhere in a parent chain.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.