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How to implement a multi-CDN strategy

blog.streamroot.io

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Re: How to implement a multi-CDN strategy

#31

Post by adrianmonk »

SilasX wrote: post #2

Shower thought: what if html/http/browsers supported, as a primitive, the concept of "fetch this asset from url A, or if that doesn't work, B, or if that doesn't work, C ..."?

I think that could be very beneficial. If it were a built in feature for HTTP (or more broadly level, maybe TCP/IP), it would not only save people the hassle of reinventing the wheel, it would also be easier to ensure it's on by default for all static resources and thus get benefit across the board.

Perhaps it could be done in a flexible, extensible way as well. Create a limited language (no loops or dangerous stuff) to express policy, search order, etc. And design it so the client side doesn't necessarily have carte blanche and the server side can maintain some control if necessary.

Re: How to implement a multi-CDN strategy

#32

Post by toast0 »

gstaro wrote: post #7
SilasX wrote: post #2

Shower thought: what if html/http/browsers supported, as a primitive, the concept of "fetch this asset from url A, or if that doesn't work, B, or if that doesn't work, C ..."?

Can't you do that with DNS records where there are multiple IPs on a A record? Basically, we're already doing this for fault tolerance and load balancing within a single CDN. Except that currently we randomize the IPs. To enforce priorities, you'd want the IPs in the A record at least partially ordered by provider.

Multiple IPs on an A record works to some extent, most (many?) browsers will silently retry another ip from the list if some of the IPs don't accept a connection; I don't know if they'll try another IP on timeout though.

But you can't actually expect any ordering to make it through to the client. Your authoritative server may reorder the records, their recursive server may reorder the records, and the client resolution library may also reorder the records. There's actually an RFC advocating reordering records in client libraries; it's fairly misguided, but it exists in the wild. Reordering is also likely to happen in OS dns caches where those are used.

Re: How to implement a multi-CDN strategy

#33

Post by Jormundir »

jloveless wrote: post #22

This is a nicely written article, however it's worth noting that the performance/reliability/availability differences across CDNs at a particular moment in time are pretty much non existent. These providers share the same backbone networks, same IX PoPs etc and thereby have little diversification benefit. See https://blog.edgemesh.com/understanding-diversification-netw... ) Where multi-CDN really shines is helping wi…

This statement is not even close to true. At a particular point in time, different CDNs can have very different performance even for the same ISP in the same region.

Re: How to implement a multi-CDN strategy

#35

Post by jniedrauer »

mahesh_rm wrote: post #34

Using this comment thread to plug a question: Is there a way to use Cloudflare (or other DNS server providers) in order to dynamically fallback to CDN A (e.g. Cloudfront) in case CDN B (e.g. Netlify CDN) is down?

You can control DNS failover with custom health checks in AWS Route 53. You can also do latency based routing. I can't speak for Cloudflare, but I imagine they have similar capability.

Re: How to implement a multi-CDN strategy

#37

Post by robocat »

tyingq wrote: post #5
SilasX wrote: post #2

Shower thought: what if html/http/browsers supported, as a primitive, the concept of "fetch this asset from url A, or if that doesn't work, B, or if that doesn't work, C ..."?

Internal browser support for local caching based on a hash versus "where it came from" would be helpful as well.

The problem is that that leaks information about your viewing habits on one site, to another.

Re: How to implement a multi-CDN strategy

#38

Post by edaemon »

mahesh_rm wrote: post #34

Using this comment thread to plug a question: Is there a way to use Cloudflare (or other DNS server providers) in order to dynamically fallback to CDN A (e.g. Cloudfront) in case CDN B (e.g. Netlify CDN) is down?

I don't think Cloudflare Load Balancing can do this (yet), but Dyn can: https://dyn.com/active-failover/

The crucial part is CNAME compatibility. Most DNS services I've had experience with can only do failover between IPs.

Re: How to implement a multi-CDN strategy

#39

Post by [deleted] »

Jormundir wrote: post #33
jloveless wrote: post #22

This is a nicely written article, however it's worth noting that the performance/reliability/availability differences across CDNs at a particular moment in time are pretty much non existent. These providers share the same backbone networks, same IX PoPs etc and thereby have little diversification benefit. See https://blog.edgemesh.com/understanding-diversification-netw... ) Where multi-CDN really shines is helping wi…

This statement is not even close to true. At a particular point in time, different CDNs can have very different performance even for the same ISP in the same region.

[deleted]

Re: How to implement a multi-CDN strategy

#40

Post by joshenders »

Jormundir wrote: post #33
jloveless wrote: post #22

This is a nicely written article, however it's worth noting that the performance/reliability/availability differences across CDNs at a particular moment in time are pretty much non existent. These providers share the same backbone networks, same IX PoPs etc and thereby have little diversification benefit. See https://blog.edgemesh.com/understanding-diversification-netw... ) Where multi-CDN really shines is helping wi…

This statement is not even close to true. At a particular point in time, different CDNs can have very different performance even for the same ISP in the same region.

Absolutely. If you were a CDNs only customer this may be true but the reality is that you’re not and they are always going to be over-subscribed. Having worked at a CDN provider (Cloudflare), I can tell you that they are constantly battling resource contention via DDoS or other reliability issues.

Multi-CDN is the way to go for performance and availability, though as a customer it can be challenging because you’re forced to limit your configuration to the lowest common denominator of features and there’s not a great way to test consistency of your configurations across all vendors.

This article is essentially a high level sales pitch though; I didn’t find it all that useful. I implemented multi-CDN at Pinterest using Cedexis (DNS based), though with modern DNS providers like NSOne, Cloudflare, Dynect, a modern spark-based ETL pipeline, and the browser navigation timing API (RUM), it wouldn’t be too challenging to build something resembling Cedexis yourself.

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