Blueprints¶
Blueprints are python classes that dynamically build CloudFormation templates. Where
you would specify a raw Cloudformation template in a stack using the template_path
key,
you instead specify a blueprint python file using the class_path
key.
Traditionally blueprints are built using troposphere, but that is not absolutely necessary. You are encouraged to check out the library of publicly shared Blueprints in the stacker_blueprints package.
Making your own should be easy, and you can take a lot of examples from stacker_blueprints. In the end, all that is required is that the Blueprint is a subclass of stacker.blueprints.base and it have the following methods:
# Initializes the blueprint
def __init__(self, name, context, mappings=None):
# Updates self.template to create the actual template
def create_template(self):
# Returns a tuple: (version, rendered_template)
def render_template(self):
Variables¶
A Blueprint can define a VARIABLES
property that defines the variables
it accepts from the Config Variables.
VARIABLES
should be a dictionary of <variable name>: <variable
definition>
. The variable definition should be a dictionary which
supports the following optional keys:
- type:
- The type for the variable value. This can either be a native python type or one of the Variable Types.
- default:
- The default value that should be used for the variable if none is provided in the config.
- description:
- A string that describes the purpose of the variable.
- validator:
- An optional function that can do custom validation of the variable. A
validator function should take a single argument, the value being validated,
and should return the value if validation is successful. If there is an
issue validating the value, an exception (
ValueError
,TypeError
, etc) should be raised by the function. - no_echo:
- Only valid for variables whose type subclasses
CFNType
. Whether to mask the parameter value whenever anyone makes a call that describes the stack. If you set the value to true, the parameter value is masked with asterisks (*). - allowed_values:
- Only valid for variables whose type subclasses
CFNType
. The set of values that should be allowed for the CloudFormation Parameter. - allowed_pattern:
- Only valid for variables whose type subclasses
CFNType
. A regular expression that represents the patterns you want to allow for the CloudFormation Parameter. - max_length:
- Only valid for variables whose type subclasses
CFNType
. The maximum length of the value for the CloudFormation Parameter. - min_length:
- Only valid for variables whose type subclasses
CFNType
. The minimum length of the value for the CloudFormation Parameter. - max_value:
- Only valid for variables whose type subclasses
CFNType
. The max value for the CloudFormation Parameter. - min_value:
- Only valid for variables whose type subclasses
CFNType
. The min value for the CloudFormation Parameter. - constraint_description:
- Only valid for variables whose type subclasses
CFNType
. A string that explains the constraint when the constraint is violated for the CloudFormation Parameter.
Variable Types¶
Any native python type can be specified as the type
for a variable.
You can also use the following custom types:
TroposphereType¶
The TroposphereType
can be used to generate resources for use in the
blueprint directly from user-specified configuration. Which case applies depends
on what type
was chosen, and how it would be normally used in the blueprint
(and CloudFormation in general).
Resource Types¶
When type
is a Resource Type, the value specified by the user in the
configuration file must be a dictionary, but with two possible structures.
When many
is disabled, the top-level dictionary keys correspond to
parameters of the type
constructor. The key-value pairs will be used
directly, and one object will be created and stored in the variable.
When many
is enabled, the top-level dictionary keys are resource titles,
and the corresponding values are themselves dictionaries, to be used as
parameters for creating each of multiple type
objects. A list of those
objects will be stored in the variable.
Property Types¶
When type
is a Property Type the value specified by the user in the
configuration file must be a dictionary or a list of dictionaries.
When many
is disabled, the top-level dictionary keys correspond to
parameters of the type
constructor. The key-value pairs will be used
directly, and one object will be created and stored in the variable.
When many
is enabled, a list of dictionaries is expected. For each element,
one corresponding call will be made to the type
constructor, and all the
objects produced will be stored (also as a list) in the variable.
Optional variables¶
In either case, when optional
is enabled, the variable may have no value
assigned, or be explicitly assigned a null value. When that happens the
variable’s final value will be None
.
Example¶
Below is an annotated example:
from stacker.blueprints.base import Blueprint
from stacker.blueprints.variables.types import TroposphereType
from troposphere import s3, sns
class Buckets(Blueprint):
VARIABLES = {
# Specify that Buckets will be a list of s3.Bucket types.
# This means the config should a dictionary of dictionaries
# which will be converted into troposphere buckets.
"Buckets": {
"type": TroposphereType(s3.Bucket, many=True),
"description": "S3 Buckets to create.",
},
# Specify that only a single bucket can be passed.
"SingleBucket": {
"type": TroposphereType(s3.Bucket),
"description": "A single S3 bucket",
},
# Specify that Subscriptions will be a list of sns.Subscription types.
# Note: sns.Subscription is the property type, not the standalone
# sns.SubscriptionResource.
"Subscriptions": {
"type": TroposphereType(sns.Subscription, many=True),
"description": "Multiple SNS subscription designations"
},
# Specify that only a single subscription can be passed, and that it
# is made optional.
"SingleOptionalSubscription": {
"type": TroposphereType(sns.Subscription, optional=True),
"description": "A single, optional SNS subscription designation"
}
}
def create_template(self):
t = self.template
variables = self.get_variables()
# The Troposphere s3 buckets have already been created when we
access variables["Buckets"], we just need to add them as
resources to the template.
[t.add_resource(bucket) for bucket in variables["Buckets"]]
# Add the single bucket to the template. You can use
`Ref(single_bucket)` to pass CloudFormation references to the
bucket just as you would with any other Troposphere type.
single_bucket = variables["SingleBucket"]
t.add_resource(single_bucket)
subscriptions = variables["Subscriptions"]
optional_subscription = variables["SingleOptionalSubscription"]
# Handle it in some special way...
if optional_subscription is not None:
subscriptions.append(optional_subscription)
t.add_resource(sns.Topic(
TopicName="one-test",
Subscriptions=))
t.add_resource(sns.Topic(
TopicName="another-test",
Subscriptions=subscriptions))
A sample config for the above:
stacks:
- name: buckets
class_path: path.to.above.Buckets
variables:
Buckets:
# resource name (title) that will be added to CloudFormation.
FirstBucket:
# name of the s3 bucket
BucketName: my-first-bucket
SecondBucket:
BucketName: my-second-bucket
SingleBucket:
# resource name (title) that will be added to CloudFormation.
MySingleBucket:
BucketName: my-single-bucket
Subscriptions:
- Endpoint: one-lambda
Protocol: lambda
- Endpoint: another-lambda
Protocol: lambda
# The following could be ommited entirely
SingleOptionalSubscription:
Endpoint: a-third-lambda
Protocol: lambda
CFNType¶
The CFNType
can be used to signal that a variable should be submitted
to CloudFormation as a Parameter instead of only available to the
Blueprint when rendering. This is useful if you want to leverage AWS-
Specific Parameter types (e.g. List<AWS::EC2::Image::Id>
) or Systems
Manager Parameter Store values (e.g. AWS::SSM::Parameter::Value<String>
).
See stacker.blueprints.variables.types
for available subclasses of the
CFNType
.
Example¶
Below is an annotated example:
from stacker.blueprints.base import Blueprint
from stacker.blueprints.variables.types import (
CFNString,
EC2AvailabilityZoneNameList,
)
class SampleBlueprint(Blueprint):
VARIABLES = {
"String": {
"type": str,
"description": "Simple string variable",
},
"List": {
"type": list,
"description": "Simple list variable",
},
"CloudFormationString": {
"type": CFNString,
"description": "A variable which will create a CloudFormation Parameter of type String",
},
"CloudFormationSpecificType": {
"type": EC2AvailabilityZoneNameList,
"description": "A variable which will create a CloudFormation Parameter of type List<AWS::EC2::AvailabilityZone::Name>"
},
}
def create_template(self):
t = self.template
# `get_variables` returns a dictionary of <variable name>: <variable
value>. For the subclasses of `CFNType`, the values are
instances of `CFNParameter` which have a `ref` helper property
which will return a troposphere `Ref` to the parameter name.
variables = self.get_variables()
t.add_output(Output("StringOutput", variables["String"]))
# variables["List"] is a native list
for index, value in enumerate(variables["List"]):
t.add_output(Output("ListOutput:{}".format(index), value))
# `CFNParameter` values (which wrap variables with a `type`
that is a `CFNType` subclass) can be converted to troposphere
`Ref` objects with the `ref` property
t.add_output(Output("CloudFormationStringOutput",
variables["CloudFormationString"].ref))
t.add_output(Output("CloudFormationSpecificTypeOutput",
variables["CloudFormationSpecificType"].ref))
Utilizing Stack name within your Blueprint¶
Sometimes your blueprint might want to utilize the already existing stack name within your blueprint. Stacker provides access to both the fully qualified stack name matching what’s shown in the CloudFormation console, in addition to the stacks short name you have set in your YAML config.
Referencing Fully Qualified Stack name¶
The fully qualified name is a combination of the Stacker namespace + the short name (what you set as name in your YAML config file). If your stacker namespace is StackerIsCool and the stacks short name is myAwesomeEC2Instance, the fully qualified name would be:
StackerIsCool-myAwesomeEC2Instance
To use this in your blueprint, you can get the name from context. The
self.context.get_fqn(self.name)
Referencing the Stack short name¶
The Stack short name is the name you specified for the stack within your YAML config. It does not include the namespace. If your stacker namespace is StackerIsCool and the stacks short name is myAwesomeEC2Instance, the short name would be:
myAwesomeEC2Instance
To use this in your blueprint, you can get the name from self.name: self.name
Example¶
Below is an annotated example creating a security group:
# we are importing Ref to allow for CFN References in the EC2 resource. Tags
# will be used to set the Name tag
from troposphere import Ref, ec2, Tags
from stacker.blueprints.base import Blueprint
# CFNString is imported to allow for stand alone stack use
from stacker.blueprints.variables.types import CFNString
class SampleBlueprint(Blueprint):
# VpcId set here to allow for blueprint to be reused
VARIABLES = {
"VpcId": {
"type": CFNString,
"description": "The VPC to create the Security group in",
}
}
def create_template(self):
template = self.template
# Assigning the variables to a variable
variables = self.get_variables()
# now adding a SecurityGroup resource named `SecurityGroup` to the CFN template
template.add_resource(
ec2.SecurityGroup(
"SecurityGroup",
# Refering the VpcId set as the varible
VpcId=variables['VpcId'].ref,
# Setting the group description as the fully qualified name
GroupDescription=self.context.get_fqn(self.name),
# setting the Name tag to be the stack short name
Tags=Tags(
Name=self.name
)
)
)
Testing Blueprints¶
When writing your own blueprints its useful to write tests for them in order to make sure they behave the way you expect they would, especially if there is any complex logic inside.
To this end, a sub-class of the unittest.TestCase class has been provided: stacker.blueprints.testutil.BlueprintTestCase. You use it like the regular TestCase class, but it comes with an addition assertion: assertRenderedBlueprint. This assertion takes a Blueprint object and renders it, then compares it to an expected output, usually in tests/fixtures/blueprints.
Examples of using the BlueprintTestCase class can be found in the stacker_blueprints repo. For example, see the tests used to test the Route53 DNSRecords Blueprint and the accompanying output results:
Yaml (stacker) format tests¶
In order to wrap the BlueprintTestCase tests in a format similar to stacker’s stack format, the YamlDirTestGenerator class is provided. When subclassed in a directory, it will search for yaml files in that directory with certain structure and execute a test case for it. As an example:
---
namespace: test
stacks:
- name: test_stack
class_path: stacker_blueprints.s3.Buckets
variables:
var1: val1
When run from tests, this will create a template fixture file called test_stack.json containing the output from the stacker_blueprints.s3.Buckets template.
Examples of using the YamlDirTestGenerator class can be found in the stacker_blueprints repo. For example, see the tests used to test the s3.Buckets class and the accompanying fixture. These are generated from a subclass of YamlDirTestGenerator.