id.rb

def save!
    post = Post.new(user: user, text: 'text')
    comment = Comment.new(post: post, text: 'text')

    exec = IdempotentExecutor.new(user_id: user.id, transaction_type: :post_create, signature: 'abcdefg')
    exec.idempotent_transaction do
 
      Post.transaction do
          post.save!
          comment.save!
      end
  
    end
  
    sns_publisher.publish!(post)
end

post.rb

def save!
    post = Post.new(user: user, text: 'text')
    comment = Comment.new(post: post, text: 'text')

    Post.transaction do
        post.save!
        comment.save!
    end

    sns_publisher.publish!(post)
end