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Orchestration == CICD
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# CloudFormation
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- Currently, we have been doing a lot of manual work
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- All this manual work will be very tough to reproduce:
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- In another region
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- In another AWS account
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- Within the same region if everything was deleted
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- Wouldn’t it be great, if all our infrastructure was... code?
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- That code would be deployed and create / update / delete our
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infrastructure
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#### What is CloudFormation?
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- CloudFormation is a declarative way of outlining your AWS Infrastructure, for any resources (most of them are supported).
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- For example, within a CloudFormation template, you want to:
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- I want a security group
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- I want two EC2 machines using this security group
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- I want two Elastic IPs for these EC2 machines
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- I want an S3 bucket
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- I want a load balancer (ELB) in front of these machines
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- Then CloudFormation creates those for you, in the right order, with the exact configuration that you specify
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**Note**: This is an introduction to CloudFormation
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- It can take over 3 hours to properly learn and master CloudFormation
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- This section is meant so you get a good idea of how it works
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- We’ll be slightly less hands-on than in other sections
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- We’ll learn everything we need to answer questions for the exam
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- The exam does not require you to actually write CloudFormation
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- The exam expects you to understand how to read CloudFormation
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#### Benefits of CloudFormation
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- Infrastructure as code
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- No resources are manually created, which is excellent for control
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- The code can be version controlled for example using git
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- Changes to the infrastructure are reviewed through code
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- Cost
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- Each resources within the stack is stagged with an identifier so you can easily see how much a stack costs you
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- You can estimate the costs of your resources using the CloudFormation template
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- Savings strategy: In Dev, you could automation deletion of templates at 5 PM and recreated at 8 AM, safely
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- Productivity
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- Ability to destroy and re-create an infrastructure on the cloud on the fly
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- Automated generation of Diagram for your templates!
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- Declarative programming (no need to figure out ordering and orchestration)
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- Separation of concern: create many stacks for many apps, and many layers. Ex:
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- PC stacks
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- Network stacks
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- App stacks
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- Don’t re-invent the wheel
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- Leverage existing templates on the web!
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- Leverage the documentation
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#### How CloudFormation works
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- Templates have to be uploaded in S3 and then referenced in CloudFormation
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- To update a template, we can’t edit previous ones. We have to re- upload a new version of the template to AWS
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- Stacks are identified by a name
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- Deleting a stack deletes every single artifact that was created by
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CloudFormation.
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#### Deploying CloudFormation templates
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- Manual way:
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- Editing templates in the CloudFormation Designer
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- Using the console to input parameters, etc
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- Automated way:
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- Editing templates in a YAML file
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- Using the AWS CLI (Command Line Interface) to deploy the templates
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- Recommended way when you fully want to automate your flow
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#### CloudFormation Building Blocks
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- Templates components (one course section for each):
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1. Resources: your AWS resources declared in the template (MANDATORY)
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2. Parameters: the dynamic inputs for your template
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3. Mappings: the static variables for your template
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4. Outputs: References to what has been created
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5. Conditionals: List of conditions to perform resource creation
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6. Metadata
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- Templates helpers:
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1. References
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2. Functions
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#### CloudFormation Resources
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- Resources are the core of your CloudFormation template (MANDATORY)
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- They represent the different AWS Components that will be created and configured
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- Resources are declared and can reference each other
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- AWS figures out creation, updates and deletes of resources for us
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- There are over 224 types of resources (!)
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- Resource types identifiers are of the form:
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- `AWS::aws-product-name::data-type-name`
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- Resource documentation:
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- I can’t teach you all of the 224 resources, but I can teach you how to learn how to use them.
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- All the resources can be found here: http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-template-resource-type-ref.html
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- Example here (for an EC2 instance): http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-instance.html
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##### Analysis of CloudFormation Templates
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- Going back to the example of the introductory section, let’s learn why it was written this way.
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- Relevant documentation can be found here:
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- http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-instance.html
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- http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-security-group.html
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- http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-ec2-eip.html
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##### FAQ for resources
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- Can I create a dynamic amount of resources?
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- No, you can’t. Everything in the CloudFormation template has to be declared.You can’t perform code generation there
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- Is every AWS Service supported?
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- Almost. Only a select few niches are not there yet
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- You can work around that using AWS Lambda Custom Resources
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#### CloudFormation Parameters
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- Parameters are a way to provide inputs to your AWS CloudFormation template
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- They’re important to know about if:
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- You want to reuse your templates across the company
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- Some inputs can not be determined ahead of time
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- Parameters are extremely powerful, controlled, and can prevent errors from happening in your templates thanks to types.
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- AWS offers us pseudo parameters in any CloudFormation template.
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- These can be used at any time and are enabled by default
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##### How to reference a parameter
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- The `Fn::Ref` function can be leveraged to reference parameters
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- Parameters can be used anywhere in a template.
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- The shorthand for this in YAML is !Ref
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- The function can also reference other elements within the template
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#### CloudFormation Mappings
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- Mappings are fixed variables within your CloudFormation Template.
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- They’re very handy to differentiate between different environments (dev vs prod), regions (AWS regions), AMI types, etc
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- All the values are hardcoded within the template
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- We use `Fn::FindInMap` to return a named value from a specific key
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#### When would you use Mapping vs. Parameters?
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- Mappings are great when you know in advance all the values that can be taken and that they can be deduced from variables such as
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- Region
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- Availability Zone
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- AWS Account
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- Environment (dev vs prod)
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- Etc...
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- They allow safer control over the template.
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- Use parameters when the values are really user specific
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#### CF Outputs
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- The Outputs section declares optional outputs values that we can import into other stacks (if you export them first)!
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- You can also view the outputs in the AWS Console or in using the AWS CLI
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- They’re very useful for example if you define a network CloudFormation, and output the variables such as VPC ID and your Subnet IDs
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- It’s the best way to perform some collaboration cross stack, as you let expert handle their own part of the stack
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- You can’t delete a CloudFormation Stack if its outputs are being referenced by another CloudFormation stack
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##### Outputs examples
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- Creating a SSH Security Group as part of one template
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- Create an output that references that security group
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##### Cross Stack Reference
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- We then create a second template that leverages that security group
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- Use the `Fn::ImportValue function`
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- You can’t delete the underlying stack until all the references are deleted too.
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#### CloudFormation Conditions
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- Conditions are used to control the creation of resources or outputs based on a condition.
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- Conditions can be whatever you want them to be, but common ones are:
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- Environment (dev / test / prod)
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- AWS Region
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- Any parameter value
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- Each condition can reference another condition, parameter value or mapping
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##### Defining Conditions
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- The logical ID is for you to choose. It’s how you name condition
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- The intrinsic function (logical) can be any of the following:
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- `Fn::And`
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`Fn::Equals`
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- `Fn::If`
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- `Fn::Not`
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- `Fn::Or`
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- Conditions can be applied to resources / outputs / etc
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#### CloudFormation Intrinsic Functions
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- Refs
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- The `Fn::Ref` function can be leveraged to reference
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- Parameters => returns the value of the parameter
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- Resources => returns the physical ID of the underlying resource (ex: EC2 ID)
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- The shorthand for this in YAML is `!Ref`
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- `Fn::GetAtt`
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- Attributes are attached to any resources you create
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- To know the attributes of your resources, the best place to look at is the documentation.
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- For example: the AZ of an EC2 machine
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- `Fn::FindInMap`
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- We use `Fn::FindInMap `to return a named value from a specific key
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- `!FindInMap [ MapName, TopLevelKey, SecondLevelKey ]`
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- `Fn::ImportValue`
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- Import values that are exported in other templates
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- Use the `Fn::ImportValue` function
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- `Fn::Join`
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- Join values with a delimiter
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- `Fn::Sub`
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- `Fn::Sub`, or `!Sub` as a shorthand, is used to substitute variables from a text. It’s a very handy function that will allow you to fully customize your templates.
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- For example, you can combine `Fn::Sub` with References or AWS Pseudo variables
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- String must contain ${VariableName} and will substitute them
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- Condition Functions (`Fn::If`, `Fn::Not`, `Fn::Equals`, etc...)
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- The logical ID is for you to choose. It’s how you name condition
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- The intrinsic function (logical) can be any of the following:
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- `Fn::And`
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- `Fn::Equals`
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- `Fn::If`
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- `Fn::Not`
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- `Fn::Or`
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#### CloudFormation Rollbacks
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- Stack Creation Fails
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- Default: everything rolls back (gets deleted).We can look at the log
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- Option to disable rollback and troubleshoot what happened
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- Stack Update Fails:
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- The stack automatically rolls back to the previous known working state
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- Ability to see in the log what happened and error messages

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