Use Of A Missing Files Host For FTP Migration

For a blog with any history, one of the most cherished features of your blog might be your search engine reputation - the ability of prospective readers to find your blog. Whenever people change blog URLs, that's one of the most anxiously asked questions in BHF: How Do I?. People preparing to move their blog from externally hosted (FTP based) publishing ask this question, too.

To satisfy your personal needs for your individual blogs, Blogger offers you three choices when migrating, from externally hosted publishing to Google hosted publishing.
  1. To Blog*Spot.
  2. To a Google custom domain URL, different from the current domain.
  3. To a Google custom domain URL, the same domain host as the current domain.

Of the three choices, the latter option, which lets you publish your blog to the same URL after migration, is going to provide the best retention of search engine reputation. If you migrate from "blog.mydomain.com" (hosted on a non Google server) to "blog.mydomain.com" (hosted on a Google server), all of the search engine reputation accumulated for "blog.mydomain.com" remains. No base URL change, no reindexing by the search engines.

When migrating an externally hosted blog, to a Google custom domain hosted at the same URL, there are several challenges.
  • The migration process can't run as one unbroken sequence. You start with the blog hosted on the external server, and your DNS addresses pointing to the external server.
    1. The Blogger migration script accesses the external server, to extract blog content, and to change content on the external server. The domain DNS must point to the external (non Google) server.
    2. You have to change the DNS addresses at the right time, to point the blog to your new Google hosting.
    3. The Blogger migration script accesses the Google server, to load blog content. The domain DNS must point to the Google server.
    You finish the migration with the blog hosted on the Google server. This must be done 1 - 2 - 3, in that order. You change the DNS addresses too soon, too late, or never - and you get no migration.
  • All post URLs will not necessarily map, identically. If the blog, hosted externally, doesn't use the precise same URL structure as Blogger hosted blog content, you're going to end up with broken links. Broken links will be bad for your readers, and for the search engines.
  • Attachments like photos, currently hosted on the external server, won't be migrated at all. If the blog contains photos hosted with the blog content (as opposed to separate hosting using Flickr, PhotoBucket, Picasa, or another third party photo host), you're going to have to leave the photos in place on the external server, until you can manually edit them into your posts using the post editor photo upload process.
To satisfy the latter two challenges, Blogger provides us the Missing Files Host option.

If you use a Missing Files Host as part of your FTP Migration strategy, Blogger lets you reference the current externally hosted blog content - photos and posts - using a secondary alias. Any broken links in your migrated blog, whether to a photo or a post, will be redirected by Blogger to your Missing Files Host.

Let's use an example. Migrate your blog, currently published as "blog.mydomain.com", from the non Google server at "nn.nn.nn.nn", to a Google custom domain server.
  1. Examine the existing DNS address for the blog.
    blog.mydomain.com. 3600 IN A nn.nn.nn.nn
  2. Setup the new DNS address for the missing files host.
    files.mydomain.com. 3600 IN A nn.nn.nn.nn
  3. Define the Missing Files Host as "files.mydomain.com", in Settings - Publishing.
  4. Define "files.mydomain.com" equal to "blog.mydomain.com", on the external server at "nn.nn.nn.nn". This is a tricky step, as it involves both you, and a technician who supports the server where your blog is (currently) hosted externally. This is not a setting which we can advise you on - but it is essential for a Missing Files Host to work properly. The external server has to contain internal pointers to your new host name "files.mydomain.com".
  5. Complete the first stage of the FTP Migration.
  6. Setup the new DNS addresses for the blog - in this example, a non root virtual host.
    blog.mydomain.com. 3600 IN CNAME ghs.google.com.
  7. Complete the second stage of the FTP migration.
When this is complete, the blog will now be published as "blog.mydomain.com", and hosted as a custom domain on a Google server. The current blog contents, hosted externally, will be edited by the migration process to point to "blog.mydomain.com" - and will respond as "files.mydomain.com", to be referenced when any existing link to "blog.mydomain.com" is broken. Any new photos and / or posts will be published to the custom domain hosted blog, on the Google server.

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