Can Jekyll use a config file from a different repo - github

Question

I'm using Jekyll and GitHub Pages to create documentation for projects that live in separate repos that are part of an organization account in GitHub. My team has decided it makes the most sense for the docs to live in each repo alongside the code, so we'll be using a gh-pages branch in each repo.
I will also be setting up a separate gh-pages repo from the organization account to serve as a landing page. I'd like to have all of my jekyll config items live in this repo. What do I need to put in the config file in each of the repos to successfully pull all of the layouts, css/scss, etc. from this central location? Is this even possible?
Here's a visual representation
In a nutshell, I'm trying to have one place where I can make changes to the website formatting files instead of 6.

Answer 1

On Github pages, you can use resources from another repository by using git submodules.
This works well for _layouts and _sass, but sadly not for _includes. This due to the fact that, in Jekyll 2.x, you cannot configure _includes folder path. This has been committed in the current master and will be available as soon as Jekyll 3 is out and used by github pages.
Edit: With Jekyll 3, you can now configure includes_dir: _mydir. See documentation for Jekyll configuration.
An interim solution can be to merge includes in layouts until you're able to configure _includes path. Not so clean, but, as your templates a centralized, it will be easy to refactor.
Howto
1 - create a resources repository
Adding your organization repository as a submodule will pull both resources, post and pages. Not a good way to go because posts and pages will be present in your project blogs.
The better way is to hosts your resources (_includes, _layouts, _sass, css) in a dedicated repository at github.com/userName/resources.
In your _layouts/default.html, dont forget to call you css with :
<link rel="stylesheet" href="{{ "/resources/css/main.css" | prepend: site.baseurl }}">
2 - Project blog Setup
Create a project blog without resources files and add the resources submodule.
git submodule add https://github.com/userName/resources.git
This creates a resources folder in you repository.
Edit your _config.yml and add:
layouts: /resources/_layouts
sass:
sass_dir: /resources/_sass
You can now jekyll serve, it works.
3 - Resources workflow
As your resources are in a submodule, changes in a template or sass file will not be reflected in your blog automatically.
In order to refresh your blog you will have to do this for all your blogs.
git submodule update --remote
git commit -a -m 'resources update'
git push origin gh-pages

Answer 2

After getting feedback from my team, I ended up doing the following:
create new repo that will be the source of the GH-Pages site
add the individual project repos as submodules of this repo
add a script that tells jekyll to pull content from specific folders in the submodules and place them in a temp dir, then use that temp dir as the build source
#remove docs-build-temp folder if it exists
rm -rf ./docs-build-temp
#make temp-content folder
mkdir ./docs-build-temp
#copy content from doc folder in submodules into temp-content folder
cp -R ./submodule1/doc ./docs-build-temp/newdir1
cp -R ./submodule2/doc ./docs-build-temp/newdir2
#tell jekyll the content source
bundle exec jekyll build -s ./docs-build-temp
The script works when run locally and in Travis CI*.
*I set up ssh authentication between my user acct in github and each of the repos in travis to get around the fact that all of them are private. Seems to be working out ok so far.