如何在 CfnInclude 期间将（可选）参数直接从 CloudFormation 模板传递到 CDK 资源而不对参数列表进行硬编码？

Question

Kind of new to these syntax, so not sure if it's achieve-able.

So we have a bunch of CloudFormation template written and we'd like to deploy them via CDK so we write code to construct them using CfnInclude . The problem is CfnInclude always require explicit parameters argument if there are parameters.

Is there a way to write these in a generic way, so we can create a whole bunch of resources via CfnInclude in just one for loop for all the CF templates, each may or may not have Parameters and the number and content of parameters is different? Cos otherwise, I'll have to supply all possible Parameters to all CF templates and then write them all out during CfnInclude .

The actual parameters' value are derived from another place and say then are put in a map, so say we know in total these CF templates may need 0, 1, 2 or 3 possible parameters from below list:

        let cfnParameters = {
            "param1": value1,
            "param2": value2,
            "param3": value3,
        };

Then can we somehow by supplying the template files themselves, write CDK in a way that it figures out how many and what parameters each file has, and then substitute them with proper values by looking up from the map (so that basically I'm passing a dynamically constructed Parameters list for each different template)? It seems like all those getParameters API only operate on the already constructed CF template as an object after CfnInclude is already called?

And I don't think we can first construct a CfnInclude without passing Parameters argument and then do GetParameters and somehow replace them with actual values right? Doc seems to say Parameter Replacement can only be done at construction time?

Answer 1

You are right, CfnInclude needs the right keys in the parameters prop, or will throw an error. No problem. Make the template's parameter replacement map before constructing CfnInclude , using language features. Read the template file. Create a map of the template's keys and the desired values. Pass the resulting map to CfnInclude .

// MyTemplateIncluder.ts

// values we want to apply
const parameters = {
  InstanceType: 'm1.large',
  KeyName: 'my-key-name',
  SSHLocation: '0.0.0.0/0',
  AnotherKey: 'anotherValue',
};

// read the template
const templatePath = path.join(__dirname, 'template.json');
const file = fs.readFileSync(templatePath, 'utf-8');
const templateParams = JSON.parse(file)?.['Parameters'] ?? {};

// new object with keys from the template and values from parameters
const replacementParameters = Object.keys(templateParams).reduce((acc, curr) => {
  acc[curr] = parameters[curr];
  return acc;
}, {});

new include.CfnInclude(this, 'MyTemplate', {
  templateFile: templatePath,
  parameters: replacementParameters,
});

Encapsulate this logic in a reusable Construct subclass. Accept parameter values and the template filename as props.