AWS Stack update error: Requires capabilities : [CAPABILITY_IAM]

Turns out you need to check a box on the last screen of the stack creation. If you are using the console, just above the 'create stack' button there's a box asking you to acknowledge that you want to allow Cloudformation to modify IAM stuff. You can, of course, create the stack without the acknowledgement, which will cause the stack to fail with the CAPABILITY_IAM error (or another error, if a different capability is required).

In CodePipeline CloudFormation you can add it like this to allow execution of the created change_set in the deploy action:

Configuration:
        StackName: !Ref GitHubRepository
        ActionMode: CHANGE_SET_REPLACE
        Capabilities: CAPABILITY_NAMED_IAM
        RoleArn: arn:aws:iam::818272543125:role/events-list-codepiplinerole
        ChangeSetName: !Join ["",[!Ref GitHubRepository, "-changeset"]]
        TemplatePath: MyAppBuild::sam_post.yaml

In the aws cli append

--capabilities CAPABILITY_IAM

or

--capabilities CAPABILITY_NAMED_IAM

To your command like this:

aws cloudformation create-stack --stack-name message-store --template-body file://bucket_with_keys.yaml --parameters file://cfg_bucket_with_keys.json --capabilities CAPABILITY_NAMED_IAM

This does not apply to cloudformation --validate-template as it is not actually creating the resources.

If you are using the AWS CLI, you can add an extra parameter to the aws cloudformation create-stack command that explicitly states you want these capabilities provided.

(this is the CLI equivalent of ticking the checkbox in the other answer here).

The parameter is --capabilities CAPABILITY_IAM, so your command would look like:

aws cloudformation create-stack --stack-name $STACK_NAME --capabilities CAPABILITY_IAM

Hope that helps