12 items tagged “cloudflare”
2024
Zero-latency SQLite storage in every Durable Object (via) Kenton Varda introduces the next iteration of Cloudflare's Durable Object platform, which recently upgraded from a key/value store to a full relational system based on SQLite.
For useful background on the first version of Durable Objects take a look at Cloudflare's durable multiplayer moat by Paul Butler, who digs into its popularity for building WebSocket-based realtime collaborative applications.
The new SQLite-backed Durable Objects is a fascinating piece of distributed system design, which advocates for a really interesting way to architect a large scale application.
The key idea behind Durable Objects is to colocate application logic with the data it operates on. A Durable Object comprises code that executes on the same physical host as the SQLite database that it uses, resulting in blazingly fast read and write performance.
How could this work at scale?
A single object is inherently limited in throughput since it runs on a single thread of a single machine. To handle more traffic, you create more objects. This is easiest when different objects can handle different logical units of state (like different documents, different users, or different "shards" of a database), where each unit of state has low enough traffic to be handled by a single object
Kenton presents the example of a flight booking system, where each flight can map to a dedicated Durable Object with its own SQLite database - thousands of fresh databases per airline per day.
Each DO has a unique name, and Cloudflare's network then handles routing requests to that object wherever it might live on their global network.
The technical details are fascinating. Inspired by Litestream, each DO constantly streams a sequence of WAL entries to object storage - batched every 16MB or every ten seconds. This also enables point-in-time recovery for up to 30 days through replaying those logged transactions.
To ensure durability within that ten second window, writes are also forwarded to five replicas in separate nearby data centers as soon as they commit, and the write is only acknowledged once three of them have confirmed it.
The JavaScript API design is interesting too: it's blocking rather than async, because the whole point of the design is to provide fast single threaded persistence operations:
let docs = sql.exec(`
SELECT title, authorId FROM documents
ORDER BY lastModified DESC
LIMIT 100
`).toArray();
for (let doc of docs) {
doc.authorName = sql.exec(
"SELECT name FROM users WHERE id = ?",
doc.authorId).one().name;
}This one of their examples deliberately exhibits the N+1 query pattern, because that's something SQLite is uniquely well suited to handling.
The system underlying Durable Objects is called Storage Relay Service, and it's been powering Cloudflare's existing-but-different D1 SQLite system for over a year.
I was curious as to where the objects are created. According to this (via Hacker News):
Durable Objects do not currently change locations after they are created. By default, a Durable Object is instantiated in a data center close to where the initial
get()request is made. [...] To manually create Durable Objects in another location, provide an optionallocationHintparameter toget().
And in a footnote:
Dynamic relocation of existing Durable Objects is planned for the future.
where.durableobjects.live is a neat site that tracks where in the Cloudflare network DOs are created - I just visited it and it said:
This page tracks where new Durable Objects are created; for example, when you loaded this page from Half Moon Bay, a worker in San Jose, California, United States (SJC) created a durable object in San Jose, California, United States (SJC).
Bringing Python to Workers using Pyodide and WebAssembly (via) Cloudflare Workers is Cloudflare’s serverless hosting tool for deploying server-side functions to edge locations in their CDN.
They just released Python support, accompanied by an extremely thorough technical explanation of how they got that to work. The details are fascinating.
Workers runs on V8 isolates, and the new Python support was implemented using Pyodide (CPython compiled to WebAssembly) running inside V8.
Getting this to work performantly and ergonomically took a huge amount of work.
There are too many details in here to effectively summarize, but my favorite detail is this one:
“We scan the Worker’s code for import statements, execute them, and then take a snapshot of the Worker’s WebAssembly linear memory. Effectively, we perform the expensive work of importing packages at deploy time, rather than at runtime.”
Weeknotes: Page caching and custom templates for Datasette Cloud
My main development focus this week has been adding public page caching to Datasette Cloud, and exploring what custom template support might look like for that service.
[... 924 words]2023
Cloudflare does not consider vary values in caching decisions. Here’s the spot in Cloudflare’s documentation where they hide a crucially important detail:
“Cloudflare does not consider vary values in caching decisions. Nevertheless, vary values are respected when Vary for images is configured and when the vary header is vary: accept-encoding.”
This means you can’t deploy an application that uses content negotiation via the Accept header behind the Cloudflare CDN—for example serving JSON or HTML for the same URL depending on the incoming Accept header. If you do, Cloudflare may serve cached JSON to an HTML client or vice-versa.
There’s an exception for image files, which Cloudflare added support for in September 2021 (for Pro accounts only) in order to support formats such as WebP which may not have full support across all browsers.
Analytics: Hacker News v.s. a tweet from Elon Musk
My post Bing: “I will not harm you unless you harm me first” really took off.
[... 817 words]Wildebeest (via) New project from Cloudflare, first quietly unveiled three weeks ago: “Wildebeest is an ActivityPub and Mastodon-compatible server”. It’s built using a flurry of Cloudflare-specific technology, including Workers, Pages and their SQLite-based D1 database.
2022
Stringing together several free tiers to host an application with zero cost using fly.io, Litestream and Cloudflare. Alexander Dahl provides a detailed description (and code) for his current preferred free hosting solution for small sites: SQLite (and a Go application) running on Fly’s free tier, with the database replicated up to Cloudflare’s R2 object storage (again on a free tier) by Litestream.
2021
1.1.1.1/purge-cache (via) Cloudflare’s 1.1.1.1 DNS service has a tool that anyone can use to flush a specific DNS entry from their cache—could be useful for assisting rollouts of new DNS configurations.
New HTTP standards for caching on the modern web (via) Cache-Status is a new HTTP header (RFC from August 2021) designed to provide better debugging information about which caches were involved in serving a request—“Cache-Status: Nginx; hit, Cloudflare; fwd=stale; fwd-status=304; collapsed; ttl=300” for example indicates that Nginx served a cache hit, then Cloudflare had a stale cached version so it revalidated from Nginx, got a 304 not modified, collapsed multiple requests (dogpile prevention) and plans to serve the new cached value for the next five minutes. Also described is $Target-Cache-Control: which allows different CDNs to respond to different headers and is already supported by Cloudflare and Akamai (Cloudflare-CDN-Cache-Control: and Akamai-Cache-Control:).
2019
Details of the Cloudflare outage on July 2, 2019 (via) Best retrospective I’ve read in a long time. The outage was caused by a backtracking regex rule that was added to the Web Application Firewall project, which rolls out globally and skips most of Cloudflare’s regular graduar rollout process (delightfully animal themed, named DOG for the dogfooding PoP that their employees use, PIG for the Guinea Pig PoPs reserved for free customers, then Canary for the final step) so that they can deploy counter-measures to newly discovered vulnerabilities as quickly as possible—but the real value in the retro is that it provides an extremely deep insight into how Cloudflare organize, test and manage their changes. Really interesting stuff.
2018
The Now CDN (via) Huge announcement from Zeit Now today: all .now.sh deployments are now served through the Cloudflare CDN, which means they benefit from 150 worldwide CDN locations that obey HTTP caching headers. This is particularly relevant for Datasette, since it serves far-future cache headers by default and uses Cloudflare-compatible HTTP/2 push hints to accelerate 302 redirects. This means that both the “datasette publish now” CLI command and the Datasette Publish web app will now result in Cloudflare-accelerated deployments.
Everyone can now run JavaScript on Cloudflare with Workers. This is such a brilliant piece of software design: Cloudflare took the service workers spec and used it as the basis for their edge-executed JacaScript feature. This means you can run server-side JavaScript in hundreds of edge locations worldwide, applying custom dynamic logic (including additional async cached fetch() calls) with only around 1ms if additional overhead. The pricing model is a steal: $0.50 per million requests with a $5/month minimum.