How to solve duplicate contents over different domains?

Question

I'm trying to create a big main site and many sister sites. They all will be hosted in a same server, but will be multiple domains.

When a sister site posts an article, it is submitted to the main site. For example, if the sister site posts an article sistersite.com/article/seo-optimization, the main site will have immediately a new article page mainsite.com/article/seo-optimization. This can definitely lead duplicate contents across different domains.

I have known that the search engines don't like the duplicate contents. The main site may have SEO penalties because of those duplicate contents. I want the main site winning over the sister sites in terms of SERP ranking. I'm thinking the following options:

1. Adding noindex, follow for the sister sites
2. Adding a canonical URL mainsite.com/article/seo-optimization in that page of the sister site.
3. Updating the content by a moderator for the main site before publishing once it receives a new article.

All of these have some pitfalls:

1. May all of the sister sites not be listed in SERP because of noindex? I want them listed somehow in SERP.
2. Is it really a valid canonical URL if it is referring to another domain? In fact, I don't want the main site URL included in the source code of the sister sites.
3. It will have work-overloads for the moderator because there may be many articles submtting a day. And how does Google decide what are duplicate contents? For example, 80% of the contents is same, 90% of the contents is same, etc.

What would be a best solution to solve duplicate contents over different domains?

Answer 1

I don't really know why you want to copy content over domains whereas Google is fighting this kind of practice.

However, the better idea I see for your case is to create on the main site a news aggregator of all articles from sisters sites. You can follow these steps:

1. Create a new article with good content on a sister site
2. Detect it on the main site, create a new page (not published)
3. For the new page, ask a moderator to write a short description (around 300 characters minimum, more is better) and link the sister site article
4. Publish the new page on the main site with original and non duplicate content

This is the only way I see to be able to:

1. don't have duplicate content issues (thus avoiding SEO penalties)
2. index all pages (those from main site and those from sisters sites)
3. get all news from sisters sites on the main site (to make the main site bigger)
4. create a SEO optimized sites "network"

The pitfalls of this method are:

1. it takes time to write a short description of all sister site new article (find serious moderators)
2. you link the sisters sites articles from the main site and give some SEO link juice to sisters sites.

However, you have a main site with always fresh content (Google loves this) and if you get some good backlinks for the main site, I think you can have a main site winning over the sisters sites in terms of SEO. Besides, visitors of the main site will may be interested by following your news aggregator site and could put natural backlinks to you (link-baiting).

For your information, if you use noindex or canonical tag, you're going to have some non indexed articles. Moreover, Google considers duplicate content between two pages and there is no valid percentage to know, just avoid it.