Parallelizing Downloads Across Hostnames

 Parallelizing Downloads Across Hostnames


Domain sharding can have a negative effect on performance if not done right. This is because it adds DNS request time as well as connection time to each new concurrent connection on the shard. However, if utilized correctly as illustrated below, you can drastically improve resource load time.

How to Improve Resource Load Time with Domain Sharding

You can parallelize downloads across hostnames with MaxCDN by creating multiple custom domains (CNAME records) and pointing them to the CDN URL (e.g.

It’s recommended you create between two to four custom domains (see CNAME records tutorial). After creating CNAME records, they need to be added under zone settings within “Custom Domains List” in your MaxCDN Control Panel.

MaxCDN Custom Domain Settings

There is a propagation time for DNS records that you can monitor with online tools like the Global DNS Propagation Checker.

NoteWhen using this tool, keep in mind green checkmarks indicate that CNAME is propagated and is working at the specified location. If you are switching from existing records, you need to make sure that new ones are applied and propagated.

DNS Propagation Checking Tool

SEO BenefitUtilizing parallel downloads can improve SEO. Why? Well in order to implement parallel downloads across host names, multiple CNAMEs need to point to your CDN (as described above). Since you are creating CNAMEs under your main domain DNS, search engines will treat your assets with more love as they are coming from a subdomain of your domain.

The sample below shows a single domain being used to load assets. As you can see, parallel downloading is severely limited.

Asset Downloads with no hostname parallelization

The chart below illustrates how files are downloaded when domain sharding or hostname parallelization is implemented. (The difference is quite obvious.)

Asset Downloads with no hostname parallelization

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