CODEWITHSUNDEEP
amazon-web-servicesaws-cloudformation
S.N
S.N

Reputation: 5140

AWS CloudFormation template - Required values

When we define parameters and refer it within Resources, the existence of parameter value is only checked upon stack creation; and if we fail to mention parameter value, then the stack creation fails and rollback with exception such as below

Parameter validation failed: parameter value for parameter name xxx does not exist. Rollback requested by user.

I know why and is clear from the general requirement of parameters in AWS Cloud Formation document.

• Each parameter must be assigned a value at runtime for AWS CloudFormation to successfully provision the stack.

However, what I would like to is to indicate users to when they fail to mention parameter values much before stack creation.

Question: Is there a way by which we could enforce to enter parameter's value before proceeding with stack creation ?

For example, if we fail to mention stack name, console won't let you proceed. I would like something similar where it stop stack creation from proceeding if there a missing value. This image has nothing to do with my question; but to show you what I would like for my custom parameter to display in case of missing value

Update: If someone like similar feature then following are sample solutions where parameter 'Name' constrain use to enter least a char before proceeding and 'SecuritygroupIngressCIDR' enforce a valid IP.

Parameters:
  Name:
    Type: String
    AllowedPattern: ^[a-zA-Z0-9]*$
    MinLength: 1
    
  SecurityGroupIngressCIDR:
    Description: The IP address range that can be used to communicate to the EC2 instances
    Type: String
    MinLength: '9'
    MaxLength: '18'
    AllowedPattern: (\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})/(\d{1,2})
    ConstraintDescription: must be a valid IP CIDR range of the form x.x.x.x/x.

SampleVisual

Upvotes: 0

Views: 1796

Answers (2)

Marcin
Marcin

Reputation: 238081

As @Paolo said, this is the way it is usually done. A complementary example would be:

Parameters:
  Name:
    Type: String
    AllowedPattern: ^[a-zA-Z0-9]*$
    MinLength: 1

It is worth nothing that this will only error out when you hit Create stack which is the step 4 in the console. Not at the same time when you specify the parameters or stack name (Step 2).

Upvotes: 0

Paolo
Paolo

Reputation: 26014

You can combine AllowedPattern and Constraint description for the parameter.

From the documentation:

AllowedPattern
A regular expression that represents the patterns to allow for String types

ConstraintDescription
A string that explains a constraint when the constraint is violated.

Upvotes: 2

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