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AWS CloudFormation Tutorials

AWS CloudFormation Tutorials

  • Simplifies our Infrastructure Management.
  • Quickly replicates our infrastructure.
  • Easily controls and tracks changes to our infrastructure.

 How does CloudFormation works?

How does CloudFormation works

 

Cloudformation ResourcesCloudformation Template Anatomy

Stack Core Features

  • Create Stack
  • Update Stack
  • Create Change Set
  • Roll back

Stack

  • Managing collection of AWS resources as a single unit is called stack.
  • We can create, update, delete the collection of AWS resources by creating, updating and deleting stacks.
  • To create AWS resources, we create a stack by submitting the template that we created, AWS CloudFormation provisions all those resources automatically for us.

Change Set

  • If we want to make changes to our stack, we can update the stack.
  • Before making changes to resources, we can generate a change set, which is summary of proposed changes.
  • Change sets allow us to see how our changes might impact current running resources in a stack especially for critical resources, before implementing them we get an idea about the impact.
  • For example: If we associate a new keypair to ec2 instance, AWS will delete the current ec2 instance and replaces it with new ec2 instance by adding new keypair to it.

What is Resources

  • Resources are key components of a stack.
  • Resources section is a required section that need to be defined in cloud formation template.

What is parameter

Parameters: Parameters enable us to input custom values to our template each time when we create or update stack.

  • We can have maximum of 60 parameters in a cfn template.
  • Each parameter must be given a logical name (logical id) which must be alphanumeric and unique among all logical names within the template.
  • Each parameter must be assigned a parameter type that is supported by AWS CloudFormation.
  • Each parameter must be assigned a value at runtime for AWS CloudFormation to successfully provision the stack. We can optionally specify a default value for AWS CloudFormation to use unless another value is provided.
  • Parameters must be declared and referenced within the same template.
  • We can reference parameters from the Resources and Outputs sections of the template.

What is mapping

  • Mappings section matches a key to a corresponding set of named values.
  • For example, if we want to set values based on a region, we can create a mapping that uses region name as a key and contains the values we want to specify for each region
  • We can use Fn::FindInMap intrinsic function to retrieve values in map.

Intrinsic Function: FindInMap

The intrinsic function FindInMap returns the value corresponding to keys in a two-level map that is declared in Mappings section.

Parameters

  • Map Name
  • Top Level Key
  • Second Level Key
  • Return Value

Conditions

  • Conditions section contains statements that define the circumstances under which entities are created or configured.
  • Example: 1 – We can create a condition and then associate it with a resource or output so that AWS CloudFormation only creates the resource or output if the condition is true.
  • Example:2 – We can associate the condition with a property so that AWS CloudFormation only sets the property to a specific value if the condition is true, if the condition is false, AWS CloudFormation sets the property to a different value that we specify.
  • We will use conditions, when we want to re-use the template in different contexts like dev and prod environments.
  • Conditions are evaluated based on predefined Psuedo parameters or input parameter values that we specify when we create or update stack.
  • Within each condition we can reference the other condition.
  • We can associate these conditions in three places.
    • Resources
    • Resource Properties
    • Outputs

 

  • At stack creation or stack update, AWS CloudFormation evaluates all conditions in our template. During stack update, Resources that are now associated with a false condition are deleted.
  • Important Note: During stack update, we cannot update conditions by themselves. We can update conditions only when we include changes that add, modify or delete resources.

Outputs

  • Outputs section declares output values that we can
  • Import in to other stacks (to create cross-stack references)
  • When using Nested stacks, we can see how outputs of a nested stack are used in Root Stack.
  • We can view outputs on the CloudFormation console
  • We can declare maximum of 60 outputs in a cfn template.

 

Export (Optional)

  • Exports contain resource output used for cross-stack reference.
  • For each AWS account, Export name must be unique with in the region. As it should be unique we can use the export name as “AWS::StackName”-ExportName
  • We can’t create cross-stack references across regions.
  • We can use the intrinsic function Fn::ImportValue to import values that have been exported within the same region. We will see this practically.
    • In simple terms, export availability zone in stack1 and use it stack2
  • For outputs, the value of the Name property of an Export can’t use Ref or GetAtt functions that depend on a resource.
  • We can’t delete a stack if another stack references one of its outputs.
  • We can’t modify or remove an output value that is referenced by another stack.
  • We can use Outputs in combination with Conditions. We will see that in our practice sessions for Outputs.

 Metadata

  • Metadata provides details about the cfn template.
  • We have three types of metadata keys which are listed below.
  • Metadata Keys
    • AWS::CloudFormation::Designer
    • AWS::CloudFormation::Interface
    • AWS::CloudFormation::Init

 Metadata Keys

  • AWS::CloudFormation::Designer
    • Auto generated during resources drag and drop to canvas.
  • AWS::CloudFormation::Interface
    • Used for parameter grouping.
  • AWS::CloudFormation::Init
    • Used for application installation and configurations on our aws compute (EC2 instances).
    • This is core and important feature of CloudFormation.
    • We have one complete section outlining the end to end details of init.

 Metadata :

(AWS::CloudFormation::Designer)

  • Designer, Visually depicts how our resources are laid out
  • Designer automatically add this information when we use it to create view and update templates. Its a system generated metadata.
  • It defines the information about our resources such as their size and relative position in template metadata. All layout information is stored in designer metadata.
  • In designer we drag and drop the resources.
  • When we create templates in Designer, it enforces some basic relationships between resources to help us create valid template.
  • Example: We cannot directly add EC2 instance in a VPC, we must add a subnet in a VPC.
  • We can also validate template directly in designer.
  • We can bring our template which we have written manually and validate in designer using validate template.
  • Integrated Editor:
    • We can make all our template modifications with this editor.
    • It also provides the auto-complete feature that lists all property names for a resource so we don’t need to memorize all the properties of a resource or refer documentation.
    • We can use integrated editor to convert from JSON to YAML and vice versa.

How I use Designer?

  • Firstly, I write my cfn templates manually in editor by referring documentation
    • Which gives me greater confidence on that particular resource for which I am writing template.
    • I use visual studio code as my editor due to the fact that dealing with YAML spaces is simplified in this editor. I just use tabs and VS code editor takes care of yaml spaces.
  • Copy template to Integrated Editor and Validate Template.
  • Convert template from JSON to YAML or YAML to JSON.
  • Drag resources to canvas and see their properties (some times).
  • Copy template to Integrated Editor and review template visually on canvas.

AWS::CloudFormation::Interface

  • When we create or update stacks in the console, the console lists input parameters in alphabetical order by their logical IDs.
  • By using this key, we can define our own parameter grouping and ordering so that users can efficiently specify parameter values.
  • We can also define labelsfor parameters.
  • A label is a friendly name or description that the console displays instead of a parameter’s logical ID which helps users understand the values to specify for each parameter.

EC2 UserData

CloudFormation & UserData

  • We can use UserData in CloudFormation template for ec2.
  • We need to use a intrinsic function Fn::Base64 with UserData in CFN templates. This function returns the Base64 representation of input string. It passes encoded data to ec2 Instance.
  • YAML Pipe (|): Any indented text that follows should be interpreted as a multi-line scalar value which means value should be interpreted literally in such a way that preserves newlines.
  • UserData Cons
  • By default, user data scripts and cloud-init directives run only during the boot cycle when we first launch an instance.
  • We can update our configuration to ensure that our user data scripts and cloud-init directives run every time we restart our instance. (Reboot of server required)

Helper Scripts cfn-init, cfn-hup and cfn-signal

AWS CloudFormation provides the following Python helper scripts that we can use to install software and start services on Amazon EC2 that we create as part of stack.

  • cfn-init
  • cfn-signal
  • cfn-get-metadata
  • cfn-hup

Configsets

We can create more than one config key and have cfn-init process them in a specific order.

  • Single Configset
  • Multiple Configset

Nested Stacks

  • The AWS::CloudFormation::Stack type nests a stack as a resource in a top-level template.
  • We can add output values from a nested stack within the root stack.
  • We use Fn::GetAtt function with nested stacks logical name and the name of the output value in nested stack

 

Nested Stacks – Practice – Create Templates

Step#0: Step#1: Step#2:
S3 Bucket VPC Nested Stack Template Root Stack Template
•         Create S3 bucket

•         This is required for uploading the Nested stack templates to S3

Create Parameters

• Create Metadata

• Create Resources

•         Create VPC

•         Create Subnets

•         Create Route Table

•         Associate Subnet & Route Table

•         Create IGW

•         Associate IGW to VPC

•         Create Route

• Create Outputs

• Test Template

• Upload to S3

•         Create Parameters

o   Create Resources

o   Create VPC Stack

•         Create EC2 Instance

•         Create Outputs

 

AWS CloudFormation Nested Stacks

Step#3: For VPC Nested Stack

  • Create Root Stack
  • It automatically creates the vpc nested stack

VPC Nested Stack

Step#4: Security Group Nested Stack Template

  • Create Parameters
  • Create Resources
    • Create Security Group
  • Create Outputs

Step#5: Root Stack Template

  • Create Parameters
  • Create Resources
    • Create VPC Stack
    • Create EC2 Instance
  • Create Outputs
  • Create Resource
    • Create Security Group Stack
    • Update VM Instance resource with security group

Step#6:

 Security Group Nested Stack

Step#7:

 Security Group Nested Stack

Step#8:

 Security Group Nested Stack

Nested Stacks vs Outputs

  • A nested stack is a stack that you create within another stack by using the AWS::CloudFormation::Stack (p. 954) resource. With nested stacks, you deploy and manage all resources from a single stack.
  • You can use outputs from one stack in the nested stack group as inputs to another stack in the group. This differs from exporting values.
  • If you want to isolate information sharing to within a nested stack group, we suggest that you use nested stacks. To share information with other stacks (not just within the group of nested stacks), export values.
  • For example, you can create a single stack with a subnet and then export its ID. Other stacks can use that subnet by importing its ID; each stack doesn’t need to create its own subnet. Note that as long as stacks are importing the subnet ID, you can’t change or delete it.

 

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Abhay Singh

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