Hanging a new site on an old domain - how not to lose positions in the CEO?

Question

Joomla

Hello! The essence of the question is simple, but the solution is not.
There is a site on joomla - simple, not modern, etc. The domain is about 5 years old. This site has a good position in the search results.
We made a new site on bitrix with a large catalog, a completely different structure, etc. (it was not possible to repeat the structure of the old one). We plan to hang the site on the old domain.
Which site replacement algorithm will be the least deplorable in terms of losses in search results?
There were suggestions:
- hang a new site on another domain (consonant), drive for some time (~ half a year), while not turning off the old one. Then transfer the new site to the old domain.
- hang a new site on the old domain, and leave the old site on a subdomain like "old.site.ru". But will the robot index pages in the SERP if we add a subdomain?
Both options seem meaningless, so I ask for help and advice.
Surely the topic has been ridden, on all attempts to read / find out something somewhere, there is only one answer - "there will be losses and nothing can be done about it, unless there is a 100% match between the urls of the new and the old site." I understand that there will be losses, but perhaps there is a way to at least somehow reduce them!
Thanks in advance!!!

Answer 1

301 to new urls, but the loss will be about 40% of the traffic
here you will not do anything.
accordingly, the new structure of the site will enter the index and rise, and after 2 months you will have an increase in indicators.

Answer 2

You went to the hypermarket for as long as you can remember, you know where everything is, all the shelves / racks are always in one place, and then bam, they came, they stuffed everything in a new way, it’s not clear where everything is, and for some time you will walk, study, memorize, and at first you will be shaking, they say, - "what the hell"?
Here it is the same.
The only thing that can be done here is if the pages on the old site correspond to the same content as on the new one, then I would make a redirect_from field for the infoblock, and put the urls of the old pages there, and in the component itself I would check this variable and redirect with 301 header to the new current one, if someone visited the page \ url from redirect_from
At least compare with the analogy above and hang pieces of paper with tips on the shelves (Looking for booze? It is now to the left after 3 shelves)

Answer 3

Hello!
I did something like this: I
inserted code into the file that is responsible for rewrite in which:
1) there is an array of old urls that are indexed by search engines
2) there is an array of new urls for the new version of the site
3) if the content address on the new site matches the old one, for example / contacts / then these URi are not fixed in arrays
4) Next, check if the current URL is in the array (comparison with $_SERVER["REQUEST_URI"]), then redirect like header("location: /new_uri",301,true);exit; otherwise, loading of the new cms continues
. In cases of bitrix, such code can be placed in the files /bitrix/modules/main/include/prolog_before.php and /bitrix/header.php
Thus, users who came from the search using the old links will get to the current content placement address and the search engines will understand where the content is now located.
Repeatedly tested - as a rule, positions only grew.
Regarding whether you need to hang up a new site to start with a new domain: if you use a significant number of texts in the old site, then definitely not. If a complete uniqueization has been carried out - it is necessary already according to the circumstances, it may even make sense to temporarily leave the old site on the old.domen.ru subdomain - but I suppose you, like everyone else, use old texts, so the answer is to the same domain.