I am working with a custom theme in Magento 2.1. I would like site administrators to be able to set the header logo's link via the admin config. This link would then be used in app/design/frontend/vendor/theme/Magento_Theme/templates/html/header/logo.phtml.
By default, I believe it uses $this->getUrl('') to point to the store's home page. However, I need this to point to an external URL, and the URL depends on which environment the site is running on (i.e. dev, staging, prod).
My solution was to create a redirect link, and link to that from the logo. This way, site administrators can update the link as needed.
In app/design/frontend/VENDOR/THEME/Magento_Theme/templates/html/header/logo.phtml, I changed the link to:
<a class="logo" href="<?php print $this->getUrl('sitehome');?>" title="<?php /* @escapeNotVerified */ echo $storeName ?>">
Then, in the admin at Marketing > URL Rewrites, I created a rewrite URL for "sitehome." That link goes to an external URL.
Hope this helps somebody. :)