While a content delivery network (CDN) improves service reliability and loading speeds, implementing a multi-CDN architecture enables organizations to optimize speeds, reliability, and cost. A multi-CDN strategy distributes content across multiple CDN providers to deliver content consistently while accounting for issues related to geographic location or network conditions. 

To implement this strategy, organizations need to make some difficult decisions. Some organizations may choose to leverage a third-party platform focused on CDN integration. However, for many other organizations, building their own multi-CDN provides more control that allows them to optimize their implementation. If an organization decides that building its own multi-CDN is the better option, then it needs to choose between DNS-based and API-based implementations. 

While each method has its advantages and challenges, understanding the nuances between DNS-based and API-based multi-CDN solutions is key to making the connectivity choice that best fits an organization’s unique needs.
 

Optimizing CDN: Should You Build Your Own Multi-CDN? 

When deciding whether to build a multi-CDN or leverage a platform, organizations should consider the following: 

• Assessing needs: Organizations should understand where the audience resides and the expected traffic when defining goals and key performance indicators (KPIs) that align the multi-CDN strategy with business objectives.  
• Selecting CDN providers: To achieve the intended cost reduction and delivery speed improvements, organizations should review providers’ throughput and latency, network size, geographic locations of servers, pricing model, and security optimization capabilities.  
• Building redundancy and failover mechanisms: To ensure continuous availability, organizations need to set up backup CDNs to cover any potential outages across the deployment, including accounting for local outages.  
• Traffic routing and load balancing: With smart routing to direct traffic based on network performance and user location, organizations can reduce delays and improve overall user experience.  
• Content synchronization and caching strategies: As part of maintaining a multi-CDN, organizations should have the resources to ensure that CDN nodes have up-to-date content to optimize caching, which reduces load on origin servers and speeds up responses. 
• Analytics, monitoring, and optimization: To optimize their multi-CDN's performance, organizations should monitor uptime, latency, and load times so they can adjust caching rules, which improve performance and reduce costs. 

What Is API-Based Multi-CDN? 

An API-based multi-CDN dynamically switches between different CDN providers using an API so that organizations can automatically or manually reroute traffic to the best-performing CDN at any given time. With API-based implementations, organizations can collect performance metrics by using API calls to identify the fastest or more reliable CDN so they can make data-driven switching decisions. 

Often, organizations will use a central API gateway or load balancer that sits between users and the CDNs to make real-time decisions about traffic routing. An API-based deployment prevents user requests from going directly to a specific CDN by checking which one is best and forwarding the requests accordingly. 
 

Benefits of API-Based CDN Switching 

Using APIs for CDN switching offers several benefits, including: 

• Real-time switching based on performance data  
• Granular routing on a regional, user, or page/content level basis 
• Application-layer handling to overcome challenges with internet service providers (ISPs) making caching decisions 
• Failure detection to redirect traffic 

Challenges of API-Based CDN Switching 

For many organizations, the challenges of API-based CDN switching outweigh the benefits. Some examples of these challenges include: 

• Checking and routing each request individually can increase latency 
• Complexity and maintenance costs from managing API performance 
• Service disruption from API failures 
• Throttled switching from CDN provider API request limitations

What Is DNS-based CDN Switching? 

DNS-based CDN switching leverages the DNS system to determine which CDN will serve a user’s request, often based on geographic location, load balancing, or failure conditions. When users send requests to the site, the DNS resolver queries the DNS server for the website’s IP address. 

Organizations can set up their DNS servers to resolve the domain to different IP addresses that point to different CDN providers. For example, they can point North American users to a CDN located in Canada or the United States while pointing European users to a CDN in their own country. 

The DNS record has a TTL (time period) that dictates how long the DNS resolver will cache the IP address. Once the TTL expires, the resolver will query the DNS again, potentially resulting in a switch to a different CDN if conditions change.

DNS-based CDN switching makes routing decisions based on factors like: 

• User geographical location 
• Load balancing between CDNs 
• Failover if a CDN is down

Benefits of DNS-Based CDN Switching 

DNS-based switching offers several benefits, including: 

• Ease of deployment by configuring DNS rules and TTLs 
• Consistent performance as users stay with a single CDN for their entire session 
• Delivery speed with cached DNS records requiring fewer lookups for fast page loads 
• Use of existing DNS infrastructure without purchasing additional hardware or software 
• Universally compatible with every CDN and ISP to prevent vendor lock-in 
• Flexibility and resilience by avoiding rate limits or failure points

Challenges of DNS-based CDN Switching 

For many organizations, DNS-based CDN switching enables a robust multi-CDN implementation. However, organizations should be aware of these potential challenges: 

• Changing DNS settings requires lowering the TTL for records to propagate them quickly  
• Some ISPs and browsers cache DNS records outside of the organization’s control 
• DNS-based switching happens at the DNS resolution stage, which may not account for network congestion 
• DNS-based failover relies on TTL to trigger a change if a CDN goes down

UltraDNS: The Speed and Responsiveness of API-Based CDN Switching Without The Costs  

UltraDNS Multi-CDN Management gives you control of API-based CDN switching without the costs associated with it. Our solution offers real-time analytics that enable you to automatically route your web traffic to the fastest CDN provider in a user’s region.  With UltraDNS, you can double your coverage map to ensure that users get the fastest speeds, no matter their geographic location. 

We automatically update your DNS records to point to the fastest CDN for huge performance gains, even when CDNs share the same PoPs. Our CDN load-balancing services include built-in failover and outage recovery so that you can seamlessly migrate traffic to backup providers to prevent downtime and reduce business interruption. With our global GeoDNS capabilities, you can build your own custom configurations or use our traffic steering capability to dynamically route users to the fastest servers in their region or for their specific location or network.

UltraDNS supports real-time decisions with automation that enables organizations to understand modern traffic logic. With our ability to work across small- and large-scale deployments without hiring a CDN or network specialist, you can scale your multi-CDN in alignment with your enterprise growth path by leveraging our advanced DNSSEC and analytics capabilities.