4 ms·

If you know all of your clients, then you don't even need DNS. But, you don't know all of your clients. Nor do you always know your upstream DNS provider. Desi

If you know all of your clients, then you don't even need DNS. But, you don't know all of your clients. Nor do you always know your upstream DNS provider. Design for failure. Don't fabricate failure.

zamadatix 2y ago
Why would knowing your clients change whether or not you want to use DNS? Even when you control all of the clients you'll almost always want to keep using DNS. A large number of services successfully achieve their failure tolerances via these kinds of DNS methods. That doesn't mean all services would or that it's always the best answer, it just means it's a path you can consider when designing for the needs of a system.
- latchkey 2y ago
  I'm replying to the comment above. If the article picks a few clients and it happens to work, that is effectively "knowing your clients". At which point, it means you have control over the client/server relationship and if we are trying to simplify by not using load balancers, we might as well simplify things even further, and not use DNS. It is an absurd train of thought that nobody in their right mind would consider... just like using DNS-RR as a replacement for load balancing.
  - zamadatix 2y ago
    I must be having trouble following your train of thought here - many large web services like Cloudflare and Akamai serve large volumes of content through round robin DNS balancing, what's absurd about their success? They certainly don't know every client that'll ever connect to a CDN on the internet... it just happens to work almost every time anyways. That very few clients might not instantly flip over isn't always a design failure worth deploying full load balancers. I'm also still not following why the decisions for whether or not you need a load balancer are supposed to be in any way equivalent to the decisions of when using DNS would make sense or not?
    - latchkey 2y ago
      We are not talking about "large web services", we are talking about small end users spinning up their own DNS-RR "solution". LWS get away with it because of Anycast... https://www.cloudflare.com/en-gb/learning/cdn/glossary/anycast-network/ https://www.cloudflare.com/en-gb/learning/cdn/glossary/anyca...
      - zamadatix 2y ago
        Anycast is certainly a nice layer to add but it's not a requirement for DNS round robin to work reliably. It does save some of the concern around relying on selection of an efficiently close choice by the client though and can be a good option for failover. More directly - is there some set of common web client I've been missing for many years that just doesn't follow DNS TTLs or try alternate records? I think the article gets it right with the wish list at the end containing a Amazon Route 53-like "pull dead entries automatically" note but maybe I'm missing something else? I've used this approach (pull the dead server entries from DNS, wait for TTL) and never caught any unexpected failures during outages but maybe I haven't been looking in the right places? If you mean it's possible to design something with round-robin DNS in a way that more clients than you expect will fail then absolutely, you can do things the wrong way with most any solution. Sometimes you can be fine with a subset of clients not always working during an outage or you can be fine with a solution which provides slower failover than an active load balancer. What I'm trying to find is why round-robin DNS must always be the wrong answer in all design cases.
        latchkey 2y ago
        > is there some set of common web client I've been missing for many years that just doesn't follow DNS TTLs or try alternate records? Yes. There are tons of people with outdated and/or buggy software still using the internet today.
        zamadatix 2y ago
        What % did you find to be "tons" with these specific bugs? I'm assuming it was quite a significant number (at least 10%?) that broke badly quite often given the certainty it's the wrong decision for all solutions, any idea how to help me identify which clients I've been missing or might run into? DNS TTLs are also pretty necessary for most web systems to work reliably, regardless of load balancer or not, so what ways do you work around having large numbers of clients which don't obey them (beyond hoping to permanently occupy the same set of IPs for the life of the service of course)?

If you know all of your clients, then you don't even need DNS. But, you don't know all of your clients. Nor do you always know your upstream DNS provider. Design for failure. Don't fabricate failure.

zamadatix 2y ago

Why would knowing your clients change whether or not you want to use DNS? Even when you control all of the clients you'll almost always want to keep using DNS. A large number of services successfully achieve their failure tolerances via these kinds of DNS methods. That doesn't mean all services would or that it's always the best answer, it just means it's a path you can consider when designing for the needs of a system.

latchkey 2y ago
I'm replying to the comment above. If the article picks a few clients and it happens to work, that is effectively "knowing your clients". At which point, it means you have control over the client/server relationship and if we are trying to simplify by not using load balancers, we might as well simplify things even further, and not use DNS. It is an absurd train of thought that nobody in their right mind would consider... just like using DNS-RR as a replacement for load balancing.
- zamadatix 2y ago
  I must be having trouble following your train of thought here - many large web services like Cloudflare and Akamai serve large volumes of content through round robin DNS balancing, what's absurd about their success? They certainly don't know every client that'll ever connect to a CDN on the internet... it just happens to work almost every time anyways. That very few clients might not instantly flip over isn't always a design failure worth deploying full load balancers. I'm also still not following why the decisions for whether or not you need a load balancer are supposed to be in any way equivalent to the decisions of when using DNS would make sense or not?
  - latchkey 2y ago
    We are not talking about "large web services", we are talking about small end users spinning up their own DNS-RR "solution". LWS get away with it because of Anycast... https://www.cloudflare.com/en-gb/learning/cdn/glossary/anycast-network/ https://www.cloudflare.com/en-gb/learning/cdn/glossary/anyca...
    - zamadatix 2y ago
      Anycast is certainly a nice layer to add but it's not a requirement for DNS round robin to work reliably. It does save some of the concern around relying on selection of an efficiently close choice by the client though and can be a good option for failover. More directly - is there some set of common web client I've been missing for many years that just doesn't follow DNS TTLs or try alternate records? I think the article gets it right with the wish list at the end containing a Amazon Route 53-like "pull dead entries automatically" note but maybe I'm missing something else? I've used this approach (pull the dead server entries from DNS, wait for TTL) and never caught any unexpected failures during outages but maybe I haven't been looking in the right places? If you mean it's possible to design something with round-robin DNS in a way that more clients than you expect will fail then absolutely, you can do things the wrong way with most any solution. Sometimes you can be fine with a subset of clients not always working during an outage or you can be fine with a solution which provides slower failover than an active load balancer. What I'm trying to find is why round-robin DNS must always be the wrong answer in all design cases.
      - latchkey 2y ago
        > is there some set of common web client I've been missing for many years that just doesn't follow DNS TTLs or try alternate records? Yes. There are tons of people with outdated and/or buggy software still using the internet today.
        zamadatix 2y ago
        What % did you find to be "tons" with these specific bugs? I'm assuming it was quite a significant number (at least 10%?) that broke badly quite often given the certainty it's the wrong decision for all solutions, any idea how to help me identify which clients I've been missing or might run into? DNS TTLs are also pretty necessary for most web systems to work reliably, regardless of load balancer or not, so what ways do you work around having large numbers of clients which don't obey them (beyond hoping to permanently occupy the same set of IPs for the life of the service of course)?