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It occurs to me, that hosting a website on www.domain.com will result in duplicate, unnecessary DNS lookups if www is a CNAME and not an A(AAA) Record. If the CNAME points to another CNAME, things start getting messy.

WWW as an A Record: one lookup for the A record

WWW as a CNAME: one lookup for the CNAME, plus (at least) one for A record.

For the purposes of SEO, for which which speed is a measure, will this matter? Should I change all my CNAMEs to A records?

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This doesn’t matter at all in respect to SEO. SEO means having a site that is user friendly (speed, ui/ux), content that matters to a user depending on intent and lastly but most importantly - a product or service with demand.

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  • If you are concerned about user centric performance management - take a look at the RAIL model. Have code splitting in place (webpack 4), have a local server or cloudfalte If you go national, reduce js dependencies and take advantage of lazy loading wherever possible. That always does the trick. We run a successful site for £60 per month hosting - just by optimising delivery we turned super competitive ... nevermind Tecord Type
    – Georg Keferböck
    Jul 19 '19 at 10:25
  • Some will argue that about speed an A record is better than a CNAME because of less resolutions... which is not really a problem in fact due to caching and CDNs use CNAME extensively. A local IP (hence CDNs, anycast, etc.) matters probably more.
    – Patrick Mevzek
    Jul 19 '19 at 14:33
  • Hmmm ... A record is just as fast as a CNAME record when they're within the same domain, e.g. CNAME (example.com) points to A record (example.com), while a CNAME of cdn.example.com that points to a different domain like yoursite.cloudfront.net would incur an extra lookup and thus be slower. (Should add, that this is what my engineer just said - don't shoot the messenger!).
    – Georg Keferböck
    Jul 19 '19 at 16:32
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    Technically true, but when you use CNAME it is "often" because you need to point to an external provider (often a CDN), hence different zones. If you manage both parts, then you could indeed eliminate the CNAME altogether in the zone by fixing the provisioning of it. Look at www.microsoft.com for example: 3 CNAME, 4 separate zones.
    – Patrick Mevzek
    Jul 19 '19 at 16:51
  • @PatrickMevzek True and worth a thumbs up ;)
    – Georg Keferböck
    Jul 19 '19 at 17:42

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