During a webmaster video hangout on August 21, John Mueller of Google strongly recommended that those who are migrating from HTTP to HTTPs do so with 301 redirects on a per-URL basis. According to Mueller, you shouldn’t use other types of redirects. 301 redirects are what you should be sticking with for these migrations.
According to Mueller, “if you start using other kinds of HTTPS result codes for redirects, then… we kind of have to reconsider and think ‘well, are they doing something unique here that’s not just a generic site move?’” He said that will then lead Google down the path of reprocessing each and every URL, which will result in making “these moves take a lot longer and make it a lot harder for us to just pass on all of the signals to the new version of the site.”
Here is the transcript from the video:
Can we also use a 303 status code after moving from HTTP to HTTPS or as only 301 recommended?
We strongly recommend use clean 301 redirect from on a per URL basis for HTTP migrations.
So you can use other types of redirects but the 301 redirect is really the one that we watch out for. And if we can recognize that it’s really a clean migration from HTTP to HTTPS, that all of the old URLs have moved to the new one, that you’re not removing things, that you’re not noindexing or robots.txt disallowing pages differently on HTTPS. Then that makes a lot easier for us to trust that as a kind of this one big thing of a site move that is moving from HTTP to HTTPS.
So the clearer you can tell us that this is really just a generic move and we don’t have to think about any of the details, the more likely we can just switch that over without you seeing any big change at all.
So if you start using other kind of HTTPS result codes for redirects then that makes it such that we kind of have to reconsider and think ‘well, are they doing something unique here that’s not just a generic site move?’ And then, at that point, we have to reprocess really each URL individually and think like ‘well, what is the webmaster trying to do here in this specific case.’ And that makes these moves take a lot longer and makes it a lot harder for us to just pass on all of the signals to the new version of the site.
Below is the video embed. He starts talking about this at 23:20 into the video: