Similarities and Differences between CNAME record and Route 53 ALIAS record

Question

I thought all valid ES6 classes must be instantiated with a constructor.

Additionally, how does the sub-class Clock have access to the render() method of the parent class React.Component without calling super()?

 class Clock extends React.Component {
  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>It is {this.props.date.toLocaleTimeString()}.</h2>
      </div>
    );
  }
}

http://codepen.io/gaearon/pen/zKRGpo?editors=0010

Solution 1

Both CNAMEs and alias records provide a level of indirection, i.e. it's a pointer to another location which requires an additional step to find the answer. The difference is who performs this additional step.

With CNAME records the additional step is done by the client. The server simply returns the configured value of the CNAME record, and the client is responsible for then looking up that name to find the A/AAAA record.

With alias records the additional step is done by the server. The server takes the configured value of the record and actively resolves this to find the A/AAAA record. It then returns this result to the client as an A/AAAA record, and the client doesn't need to do anything to get the final answer. The client doesn't even know that the server did this, it simply sees a plain A/AAAA record.

The Route53 documentation has more detail on alias records. At the moment alias records can only point at ELB hostnames or at a hostname in the same zone.

Solution 2

CNAMEs can't be used for the domain apex (i.e. example.com) without oddities. ALIAS records act essentially like CNAMEs behind the scenes, but present themselves as A records to requesting systems.

Comments

[Zach_is_my_name]

Thanks. I typically accept an answer after I'm able to understand it. Pending

[Tom Fenech]

@Zach is that an indirect request for clarification?

[Zach_is_my_name]

Not at all. Just a curtesy note to you on my speed of processing. Ideally correct answers should receive acceptance asap. Apologies

[Tom Fenech]

I wouldn't say there's any rush to accept an answer - if anything's unclear, let me know (and update the question, if necessary).

[Zach_is_my_name]

Ok. Noted. Thanks. Personally I assumed answerers deserve and appreciate rapid gratification.

[KJH]

Update on what Alias resource record set can point to: a CloudFront distribution, an Elastic Beanstalk environment, an ELB Classic or Application Load Balancer, an Amazon S3 bucket that is configured as a static website, or another Amazon Route 53 resource record set in the same hosted zone.