This seems superficial, why not have a local-only CMS site to preview changes for the fast feedback loop and then you only have to dump the text to prod?
>got progressively worse as the amount of content grew, resulting in delays lasting tens of seconds.
This is like the only legit concern to justify redoing this, but even then, it was still only taking seconds to a minute.
They inflated the problem of “make content preview faster” for a small number of users to “make a fast global cache system”. That’s promotion material for you
"DNS domains are managed by another team."
It can be ok to admit you did something stupid, but don't brag about it like it's an accomplishment.
Concerning that their total uncompressed data size including full history is only 520MB and they built this complex distributed system rather than, say, rsyncing an sqlite database. It sounds like only Netflix staff write to the database.
So maybe it's just an attempt at unification of the tech stack, rather than a concrete need. But Hollow itself is definitely heavily used within, e.g. see its whitepaper.
In the beginning there was a need for a low-latency Java in-process database (or near cache). Soon intolerable GC pauses pushed them off the Java heap. Next they saw the memory consumption balloon: the object graph is gone and each object has to hold copies of referenced objects, all those Strings, Dates etc. Then the authors came up with ordinals, which are... I mean why not call them pointers? (https://hollow.how/advanced-topics/#in-memory-data-layout)
That is wild speculation ofc. And I don't mean to belittle the authors' effort: the really complex part is making the whole thing perform outside of simple use cases.
As much as this website could be very trafficked I have the feeling they are overcomplicating their infra, for little gains. Or at least, I wouldn't expect to end having an article about.
If it were "just" static pages, served the same to everyone, then it's pretty straightforward to implement even at the >300m users scale Netflix operates at. If you need to serve >300m _different_ pages, each built in real-time with a high-bar p95 SLO then I can see it getting complicated pretty quickly in a way that could conceivably justify this level of "over engineering".
To be honest though, I know very little about this problem beyond my intuition, so someone could tell me the above is super easy!
Otherwise known as server-side includes (SSI)
They are not talking about the Netflix steaming service.
This is a site they are talking about which is very similar to a WordPress powered PR blog.
When changes to data are important, a library like Hollow can be pretty magical. Your internal data model is always up to date across all your compute instances, and scaling up horizontally doesn't require additional data/infrastructure work.
We were processing a lot of data with different requirements: big data processed by a pipeline - NoSQL, financial/audit/transactional - relational, changes every 24hrs or so but has to be delivered to the browse fast - CDN, low latency - Redis, no latency - Hollow.
Of course there are tradeoffs between keeping a centralized database in memory (Redis) and distributing the data in memory on each instance (Hollow). There could be cases where Hollow hasn't sync'd yet, so the data could be different across compute instances. In our case, it didn't matter for the data we kept in Hollow.
What leads you to believe a CDN is a solution to a problem of delivering personalized content to a specific user?
That's not the problem.
The main requirement is to allow editors to preview their changes without having to wait multiple seconds due to caching refresh cycles.
And your response is surely “Well of course, that would be nice, but it’s not as simple as that. Here are constraints X Y and Z that make a trivial solution infeasible.”
It's 500 MB of text. A phone could serve that at the scale we're talking about here, which is a PR blog, not netflix.com.
They're struggling with "reading" from a database that is also used for "writes", a terribly difficult situation that no commercial database engine has ever solved in the past.
Meanwhile they have a complex job engine to perform complex tasks such as joining two strings together to form a complete URL instead of just a relative path.
This is pure, unadulterated architecture astronaut arrogance.
PS: This forum, right here, supports editing at a much higher level of concurrency. It also has personalised content that is visible to users with low latency. Etc, etc... All implemented without CQRS, Kafka, and so forth.
Yes many times there are very valid reasons for complexity, but my suspicion is that this is the result of 20+ very talented engineers+designers+pms being put in charge of a building a fairly basic static site. Of course you are going to get something overengineered.
I can't say whether or not it's complicated enough to justify this level of engineering. It could just be some engineers building something cool because they can, like you said.
Sometimes it’s “It was made many months/years ago in circumstances and with views that no longer seem to apply (possibly by people no longer there). Sadly, the cost of switching to something else would be significant and nobody wants to take on the risk of rewriting it because it works.”
It depends.
Then again, sometimes it only “works” by waking people up with pages multiple times a night.
All problems are trivial once you ignore all real-world constraints.
This sort of personal opinion reads like a cliche in software development circles: some rando casualy does a drive-by system analysis, cares nothing about requirements or constraints, and proceeds to apply simplistic judgement in broad strokes.
And this is then used as a foundation to go on a rant regarding complexity.
This adds nothing of value to any conceivable discussion.
- a constantly changing library across constantly changing licensing regions available in constantly changing languages
- collaborative filtering with highly personalized recommendation lists, some of which you just know has gotta be hand-tuned by interns for hyper-demographic-specific region splits
- the incredible amounts of logistics and layers upon layers of caching to minimize centralized bandwidth to serve that content across wildly different network profiles
i think that even the single-user case has mind boggling complexity, even if most of it boils down to personalization and infra logistics.
Wouldn't that be nice!
NetFlix still only supports 4 or 5 subtitle languages.
Their billions of dollars of fancy-pants infrastructure just doesn't scale to more than half a dozen of so text files.
The people talking about "read-only" didn't even bothered to read the overview of the system they are criticizing. They are literally talking out of wilful ignorance.
But here we are.
All four speakers ran the exact same slide deck with a different intro slide. All four speakers claimed the same responsibility for the same part of the architecture.
I was livid. I also stopped attending talks in person entirely because of this, outside of smaller more focused events.
There is probably some hilariously convoluted requirement to get traffic routed/internal API access. So this thing has to run in K8s or whatever, and they needed a shim to distribute the WordPress page content to it.
I cannot imagine why you'd need a reactive pipeline built on top of Kafka and Cassandra to deliver some fanservice articles through a CMS, perhaps some requirement about international teams needing to deliver tailored content to each market but even with that it seems quite overblown.
In the end it will be a technical solution to an organisational issue, some parts of their infrastructure might be quite rigid and there are teams working around that instead of with that...
Lots of people think microservices = performance gains only.
It’s not. It’s mainly for organizational efficiency. You can’t be blocked from deploying fixes or features. Always be shipping. Without breaking someone else’s code.
I don't think I ever heard that. Who claims that microservice architectures are for performance gains?
That is because they are and it seems that since they're making billions and are already profitable, they're less likely to change / optimize anything.*
Netflix is stuck with many Java technologies with all their fundamental issues and limitations. Whenever they need to 'optimize' any bottlenecks, their solution somehow is to continue over-engineering their architecture over the most tiniest offerings (other than their flagship website).
There is little reason for any startup to copy this architectural monstrosity just for attention on their engineering blog post for little to no advantage whatsoever.
* Unless you are not profitable, costs of infra continues to increase or the quality of service is sluggish or it is urgent to do so.
This is the only reasonable take in your rant, but the reasoning is off for even this. They have little reason, because they will never hit the scale Netflix operates at. In the very very odd chance they do, they will have ample money to care about it.
But many startups will die trying it anyway.
If anyone can _legitimately_ justify this, please do, I'd love to hear it.
And don't go "booohooo at scale" because I work at scale and am 100% not sure what is the problem this is solving that can't just be solved with a simpler solution.
Also this isn't "Netflix scale", Tudum is way less popular.
I hadn't even heard of it until today.
This has to be one of the most over-engineered websites out there.
If you read the overview, Tudum has to support content update events that target individual users and need to be templated.
How do you plan on generating said HTML and CSS?
If you answer something involving a background job, congratulations you're designing Tudum all over again. Now wait for opinionated drive-by critics to criticize your work as overcomplicated and resume-driven development.
Kafka might seem like extra work compared with not Kafka, but if it’s already setup and running and the entire team is using it elsewhere suddenly it’s free.
This isn't an engineering problem. It's a PM+Eng Lead failing to talk to each other problem.
If you need 20 engineers and exotic text for what should be a simple static site or Wordpress site, you're doing it wrong.
- Reddit doesn't use background jobs to render a new home page for every user after every update.
- Facebook doesn't use background jobs to render a new feed for every user after every update.
- Hacker News doesn't use background jobs to render a new feed for every user after every update.
Why? Because we have no guarantee a user will access the site on a particular day, or after a particular content update, so rendering every content update for every user is immediately the wrong approach. It guarantees a lot of work will be thrown away. The sensible way to do this is to render the page on demand, when (and IF) a user requests it.
Doing N*M work where N=<# of users> and M=<# of page updates> sure seems like the wrong approach when just doing N work where N=<# of times a user requests a page> is an option.
There's lots of less exotic approaches that work great for this basic problem:
- Traditional Server-Side Rendering. This approach is so common that basically every language has a framework for this.
- Single-Page Applications. If you have a lot of content that only needs updated sometimes, why not do the templating in the users browser?
- Maybe just use wordpress? It already supports user accounts and customization.
This is not a spectacular problem. This is a "building a web service 101 problem", which was solved about the time CGI scripts came out.
Also why would anyone involve background jobs? You can do high-performance templating real-time, especially on 2025 hardware.
Is this not what SSR html - via any backend language/framework - has been doing since forever?
Framing this as a hard-scaling problem (tudum seems mostly static, please cmiiw if thats not the case) feels like pure resume-driven engineering. Makes me wonder: what stage was this system at that they felt the need to build this?
Given how prominently 'compression' gets mentioned I was excited to learn more, but it looks like it simply amounts to using GZIPInputStream/GZIPOutputStream within the blob APIs, or am I missing something...?
The 60 second cache expiry was the issue. This is why the only sane cache policy is cache forever. Use content hashes as cache keys
Funny how they cancelled him but not the sound :-)
A few thoughts:
1) RAW Hollow sounds like it has very similar properties to Mnesia (the distributed database that comes with the Erlang Runtime System), although Mnesia is more focused on fast transactions while RAW Hollow seems more focused on read performance.
2) It seems some of this architecture was influence by the presence of a 3rd party CMS. I wonder how much impact this had on the overall design, and I would like to know some more about the constraints it imposed.
> The write part of the platform was built around the 3rd-party CMS product, and had a dedicated ingestion service for handling content update events, delivered via a webhook.
> ...
> For instance, when the team publishes an update, the following steps must occur:
>
> 1) Call the REST endpoint on the 3rd party CMS to save the data.
> 2) Wait for the CMS to notify the Tudum Ingestion layer via a webhook.
3) What is the actual daily active user count, and how much customization is possible for the users? Is it just basic theming and interests or something more? When I look through the Tudum site, it seems like it is just connected to the users netflix account. I'm assuming the personalization is fairly simple like theming, favorited shows, etc.
> Attracting over 20 million members each month, Tudum is designed to enrich the viewing experience by offering additional context and insights into the content available on Netflix.
It's unclear to me if this is users signing up for Tudum, the number of unique monthly visitors, the number of page views, or something else. I'm assuming that it is monthly active users, and that those users generally already have netflix accounts.
4) An event-driven architecture feels odd for this sort of access and use pattern. I don't understand what prevents using a single driving database, like postgres, in a more traditional pattern. By my count just the data from the CMS is also duplicated in the Hollow datastore and, implicitly, the generated pages. Of course when you duplicate data you create synchronization problems and latency. That is the nature of computing. I have always preferred to, instead, stick with just a few active copies of relevant data when practical.
> Storing three years’ of unhydrated data requires only a 130MB memory footprint — 25% of its uncompressed size in an Iceberg table!
Compressed, uncompressed, this is a comically small amount of data. High end Ryzen processors almost have this much L3 CACHE!!
As near as I can tell, writes only flow one way in this system so I don't even know if RAW Hollow needs strong read-after-write consistency. It seems like writes flow from the CMS, into RAW Hollow, and then onto the Page Builder nodes. So how does this provide anything that a postgres read-replica wouldn't?
5) Finally, the most confusing part - are they pre-building every page for every user? That seems ridiculous but it is difficult to square some of the requirements without such a thing. If you can render a page in 400 milliseconds then congratulations, you are in the realm of most good SSR applications. This would immediately save a ton of computation because there is no need to pre-build these, why not just render them on demand?
Overall this is perplexing post. I don't understand why a lot of these decisions were made and the solution seems very over-complicated for the problem as described.