3 posts tagged with "serverless"

One of the principles that shaped Juno from day one was the idea of building apps with full ownership — no hidden infrastructure, no opaque servers.

No hypocrisy either.

If developers are encouraged to deploy code in containers they control, it feels inconsistent to rely on centralized infrastructure — like AWS or other Web2 cloud providers — to manage deployment pipelines or run the platform. With the exception of email notifications, Juno currently runs entirely on the Internet Computer — and that's a deliberate choice.

That doesn't mean being stubborn for the sake of it. It just means trying to push things forward without falling back on the old way unless absolutely necessary.

At the same time, developer experience matters — a lot. It shouldn't take a degree in DevOps to ship a backend function. Developers who would typically reach for a serverless option should be able to do so here too. And for those who prefer to stay local, it shouldn't feel like a downgrade — no one should be forced into CI automation if they don't want to.

That's why the new GitHub Actions for serverless functions are now generally available — for those who want automation, not obligation.

🚀 Automated Deployments, No Compromise​

With the latest release, it's now possible to:

• Build serverless functions written in TypeScript or Rust
• Automatically publish them to a Satellite
• Optionally propose or directly apply upgrades

All within a GitHub Actions workflow. No manual builds, no extra setup — just code, commit, and push.

This makes it easier to fit Juno into an existing CI/CD pipeline or start a new one from scratch. The logic is bundled, metadata is embedded, and the container is ready to run.

🔐 What About Security?​

You might ask yourself: "But what about the risk of giving CI full control over my infrastructure?"

That's where the improved access key (previously named "Controllers") roles come in.

Instead of handing over the master key, you give CI just enough access to do its job — and nothing more.

Here's how the roles break down in plain terms:

• Administrator – Full control. Can deploy, upgrade, stop, or delete any module. Powerful, but risky for automation. Might be useful if you're spinning up test environments frequently.

• Editor (Write) – Ideal for CI pipelines that deploy frontend assets or publish serverless functions. Can't upgrade those or stop and delete modules. A good default.

• Submitter 🆕 – The safest option. Can propose changes but not apply them. Someone still needs to review and approve in the Console or CLI. No surprises, no accidents.

Use Editor for most CI tasks — it gives you automation without opening the blast radius.

Prefer an extra layer of review? Go with Submitter and keep a human in the loop.

🧰 Local or CI: Your Choice​

Nothing changes in the approach for developers who prefer local development. The CLI remains a first-class tool for building and deploying.

All the new capabilities — from publishing functions to proposing or applying upgrades — are available not just in GitHub Actions or the Console UI, but also fully supported in the CLI.

In fact, the CLI has been improved with a neat addition: you can now append --mode development to interact with the emulator. This allows you to fully mimic production behavior while developing locally. And of course, you can also use any mode to target any environment.

juno functions upgrade --mode staging
juno deploy --mode development

🛰️ Satellite's CDN​

While building serverless functions was never an issue, enabling GitHub Actions to publish and deploy without giving away full control introduced a challenge. How do you let CI push code without handing it the keys to everything?

That's where the idea of a sort of CDN came in.

Each Satellite now has a reserved collection called #_juno/releases. It's like a staging area where CI can submit new WASM containers or frontend assets. If the access key has enough privileges, the submission is deployed right away. If not, it's stored as a pending change — waiting for someone to approve it manually via the Console or CLI.

This builds on the change-based workflow that was added to the Console last year. Funny enough, it brought the Console so close to being a Satellite itself that it became… basically a meta example of what you can build with Juno.

And here's the cherry on top: because there's now a CDN tracking versions, developers can rollback or switch between different function versions more easily. A new CDN tab in the Console UI (under Functions) gives you access to all past versions and history.

🖼️ Frontend Deployments, Too​

Frontend deployment now benefits from the same change-based workflow. By default, when you run juno deploy or trigger a GitHub Action, the assets are submitted as pending changes — and applied automatically (if the access key allows it).

Want to skip that workflow? You still can. The immediate deployment path remains available — handy if something fails, or if you just prefer to keep things simple.

🛠️ GitHub Actions for Serverless Functions​

Alright, enough chit-chat — here's how to publish your serverless functions on every push to main, straight from CI:

name: Publish Serverless Functions

on:
  workflow_dispatch:
  push:
    branches: [main]

jobs:
  publish:
    runs-on: ubuntu-latest
    steps:
      - name: Check out the repo
        uses: actions/checkout@v4

      - uses: actions/setup-node@v4
        with:
          node-version: 22
          registry-url: "https://registry.npmjs.org"

      - name: Install Dependencies
        run: npm ci

      - name: Build
        uses: junobuild/juno-action@full
        with:
          args: functions build

      - name: Publish
        uses: junobuild/juno-action@full
        with:
          args: functions publish
        env:
          JUNO_TOKEN: ${{ secrets.JUNO_TOKEN }}

🌸 One Action, Two Flavors​

Noticed the @full in the previous step?

That's because the GitHub Action now comes in two flavors:

• junobuild/juno-action or junobuild/juno-action@slim – perfect for common use cases like deploying frontend assets or running simpler CLI tasks. No serverless build dependencies included, so it's faster and more "lightweight" (relatively, it still uses Docker underneath...).

• junobuild/juno-action@full – includes everything you need to build and publish serverless functions, with Rust and TypeScript support. It's heavier, but it does the job end to end.

The right tool for the right job. Pick what fits.

🧭 Where This Is Going​

This release isn't just about smoother deployments — it's a step toward making Juno feel like real infrastructure. Though, what is “real infrastructure” anyway? Whatever it is, this one doesn't come with the usual baggage.

Developers get to choose how they ship — locally or through CI. They get to decide what gets deployed and who can do it. They're not forced to rely on some big tech platform for their infra if they don't want to. And thanks to the new CDN and access control model, fast iteration and tight control can finally go hand in hand.

If you've been waiting for a way to ship backend logic without giving up on decentralization — or if you just like things working smoothly — this one's for you.

Go ahead. Build it. Push it. Submit it. Ship it.

To infinity and beyond,
David

Stay connected with Juno by following us on X/Twitter.

Reach out on Discord or OpenChat for any questions.

⭐️⭐️⭐️ stars are also much appreciated: visit the GitHub repo and show your support!

One of the goals with Juno has always been to make building decentralized, secure apps feel like something you're already used to. No weird mental models. No boilerplate-heavy magic. Just code that does what you expect, without touching infrastructure.

And with this release, we're taking another step in that direction: You can now write serverless functions in TypeScript.

If you're a JavaScript developer, you can define backend behavior right inside your container. It runs in a secure, isolated environment with access to the same hooks and assertions you'd use in a typical Juno Satellite.

No need to manage infrastructure. No need to deploy a separate service. Just write a function, and Juno takes care of the rest.

Cherry on top: the structure mirrors the Rust implementation, so everything from lifecycle to data handling feels consistent. Switching between the two, or migrating later, is smooth and intuitive.

✨ Why TypeScript?​

Rust is still the best choice for performance-heavy apps. That's not changing.

But let's be real: sometimes you just want to ship something quickly. Maybe it's a prototype. Maybe it's a feature you want to test in production. Or maybe you just want to stay in the JavaScript world because it's what you know best.

Now you can.

You get most of the same tools, like:

• Hooks that react to document or asset events (onSetDoc, onDeleteAsset, etc.)
• Assertions to validate operations (assertSetDoc, etc.)
• Utility functions to handle documents, storage, and even call other canisters on ICP

The JavaScript runtime is intentionally lightweight. While it doesn't include full Node.js support, we're adding polyfills gradually based on real-world needs. Things like console.log, TextEncoder, Blob, and even Math.random — already covered.

🔁 Designed for Interop​

The approach to writing serverless functions in Rust and TypeScript is aligned by design. That means if you outgrow your TS functions, migrating to Rust won't feel like starting from scratch. The APIs, structure, and flow all carry over.

Start scrappy, scale gracefully.

👀 A Taste of It​

Here's how simple it is to react to a document being created or updated:

import { defineHook, type OnSetDoc } from "@junobuild/functions";

export const onSetDoc = defineHook<OnSetDoc>({
  collections: ["posts"],
  run: async (context) => {
    const data = context.data.data.after.data;
    console.log("New post created:", data);
  }
});

And here's for example how you'd validate a document before accepting it — using Zod for a clean, readable schema:

import { z } from "zod";
import { defineAssert, type AssertSetDoc } from "@junobuild/functions";
import { decodeDocData } from "@junobuild/functions/sdk";

const postSchema = z.object({
  title: z.string().min(5, "Title must be at least 5 characters long")
});

export const assertSetDoc = defineAssert<AssertSetDoc>({
  collections: ["posts"],
  assert: (context) => {
    const data = decodeDocData(context.data.data.proposed.data);
    postSchema.parse(data);
  }
});

That's it. No APIs to expose, no infra to manage. Just code that runs where your data lives.

🖥️ Local-First Development​

Alongside TypeScript support, we've rethought the local development experience.

Instead of providing a partial local environment, the mindset shifted to mimicking production as closely as possible.

You still get a self-contained image with your Satellite, but now you also get the full Console UI included. That means you can manage and test your project locally just like you would on mainnet.

See this other blog post for all the details.

🧰 Zero Tooling, Just Code​

Here's the beautiful part: even though your serverless functions are written in TypeScript, they're bundled and embedded into a Satellite module that's still compiled in Rust behind the scenes.

But you don't need to install Rust. Or Cargo. Or ic-wasm. Or anything that feels complicated or overly specific.

All you need is Node.js and Docker. The container takes care of the rest: building, bundling, embedding metadata and gives you a ready-to-run Satellite that runs locally and is ready to deploy to production.

In short: just code your functions. The container does the heavy lifting.

📡 Already in the Wild​

This isn’t just a feature announcement — serverless functions in TypeScript are already live and powering real functionality.

I used them to build the ICP-to-cycles swap on cycles.watch, including all the backend logic and assertions. The whole process was documented over a few livestreams, from setup to deployment.

If you're curious, the code is on GitHub, and there’s a playlist on YouTube if you want to follow along and see how it all came together.

▶️ Try It Out​

We've put together docs and guides to help you get started. If you're already using the Juno CLI, you're just one juno dev eject away from writing your first function or start fresh with npm create juno@latest.

To infinite and beyond,
David

Stay connected with Juno by following us on X/Twitter.

Reach out on Discord or OpenChat for any questions.

⭐️⭐️⭐️ stars are also much appreciated: visit the GitHub repo and show your support!

Hey there 👋,

Are you looking to extend Juno's features? Stop right there, because it is now possible!

I'm thrilled to unveil today's new addition to the set of features offered by Juno: the introduction of serverless Functions enabling developers to extend the native capabilities of Satellites. This groundbreaking update opens a plethora of opportunities for developers to innovate and customize their applications like never before.

What Are Serverless Blockchain Functions?​

In the realm of cloud computing, serverless architecture allows developers to build and run applications and services without the burden of managing infrastructure. This model enables the execution of server-side code based on user demand, allowing for direct interactions with APIs, databases, and other resources as part of your project's deployment. It's a paradigm that significantly reduces overhead and increases the agility of software development processes.

The introduction of serverless blockchain functions by Juno innovatively takes this concept a step further by integrating blockchain technology into this flexible and efficient framework. This groundbreaking development opens the door for extending the native capabilities of Satellites smart contracts, pushing the boundaries of what's possible within the blockchain space.

This means you can now enhance the functionality of Satellites smart contracts and extend those capabilities with anything that can be achieved on the Internet Computer blockchain.

How Does It Work?​

At the core of Juno's serverless blockchain functions are hooks, which are essentially the backbone of how these functions operate within the ecosystem. These hooks are defined to automatically respond to event triggers related within your Satellite, including operations such as creating, updating, and deleting to documents and assets.

An essential feature of these optional hooks is their ability to spawn asynchronously, a design choice that significantly enhances the efficiency and responsiveness of applications built on Juno. This asynchronous spawning means that the hooks do not block or delay the execution of calls and responses between your client-side decentralized application (dApp) and the smart contract.

A picture is worth a thousand words, so here is a simplified schematic representation of a hook that is triggered when a document is set:

Getting Started​

In addition to unveiling this new feature, we're also excited to introduce a brand-new developer experience we hope you're going to enjoy. This is built on the local development environment we released earlier this year, designed to make your work with Juno smoother and more intuitive.

Start by ejecting the Satellite within your project. This step prepares your project for local development. Open your terminal and run:

juno dev eject

In a new terminal window, kick off the local development environment that leverages Docker:

juno dev start

Now, your local development environment is up and running, ready for you to start coding.

Once you're ready to see your changes in action, compile your code:

juno dev build

One of the key benefits of Juno's local development environment is its support for hot reloading. This feature automatically detects changes to your code and deploys them in the local environment. It means you can immediately test your custom code locally, ensuring a fast and efficient development cycle.

Demonstrating Hooks and Data Operations​

This sample application illustrates the use of Juno's serverless functions to perform asynchronous data operations with a small frontend client and backend hook setup.

The frontend client is designed to save a document in the Datastore, while the backend hook modifies this document upon being triggered. This process exemplifies the asynchronous capability of functions to read from and write to the Datastore.

Getting the Sample​

To begin exploring this functionality, clone the example repository and prepare the environment with the following commands:

git clone https://github.com/junobuild/examples
cd rust/hooks
npm ci

After setting up the project, to start and debug the sample in your local environment, please follow the steps as outlined in the previous chapter Getting Started.

Hook Implementation Details​

The core of this sample is the hook code, which is triggered upon the document set operation in a specific collection. Here’s the hook's logic:

#[on_set_doc(collections = ["demo"])]
async fn on_set_doc(context: OnSetDocContext) -> Result<(), String> {
    // Decode the new data saved in the Datastore
    let mut data: Person = decode_doc_data(&context.data.data.after.data)?;

    // Modify the document's data
    data.hello = format!("{} checked", data.hello);
    data.yolo = false;

    // Encode the data back into a blob
    let encode_data = encode_doc_data(&data)?;

    // Prepare parameters to save the updated document
    let doc: SetDoc = SetDoc {
        data: encode_data,
        description: context.data.data.after.description,
        updated_at: Some(context.data.data.after.updated_at),
    };

    // Save the updated document
    set_doc_store(
        context.caller,
        context.data.collection,
        context.data.key,
        doc,
    )?;

    Ok(())
}

This hook demonstrates asynchronous processing by reading the initial data saved from the frontend, modifying it, and then saving the updated version back to the Datastore. It's triggered specifically for documents within the "demo" collection and showcases how to handle data blobs, execute modifications, and interact with the Datastore programmatically.

Unlocking Anything on the Internet Computer​

As mentioned in the introduction, the serverless functions extend Juno's capabilities to anything that can be achieved on the Internet Computer. With this in mind, let's explore implementing HTTPS outcalls to a Web2 API in another sample.

Getting the Sample​

To explore this advanced functionality, follow the steps below to clone the repository and set up the project:

git clone https://github.com/junobuild/examples
cd rust/https-outcalls
npm ci

After cloning and navigating to the correct directory, proceed with starting and debugging the sample in your local environment, as outlined in the Getting Started chapter.

Hook Implementation Details​

The hook implemented in this sample interacts with the Dog CEO API to fetch random dog images and update documents within the dogs collection in the Datastore. Here's how it works:

// The data of the document we are looking to update in the Satellite's Datastore.
#[derive(Serialize, Deserialize)]
struct DogData {
    src: Option<String>,
}

// We are using the Dog CEO API in this example.
// https://dog.ceo/dog-api/
//
// Its endpoint "random" returns such JSON data:
// {
//     "message": "https://images.dog.ceo/breeds/mountain-swiss/n02107574_1118.jpg",
//     "status": "success"
// }
//
// That's why we declare a struct that matches the structure of the answer.
#[derive(Serialize, Deserialize)]
struct DogApiResponse {
    message: String,
    status: String,
}

#[on_set_doc(collections = ["dogs"])]
async fn on_set_doc(context: OnSetDocContext) -> Result<(), String> {
    // 1. Prepare the HTTP GET request
    let url = "https://dog.ceo/api/breeds/image/random".to_string();

    let request_headers = vec![];

    let request = CanisterHttpRequestArgument {
        url,
        method: HttpMethod::GET,
        body: None,
        max_response_bytes: None,
        // In this simple example we skip sanitizing the response with a custom function for simplicity reason.
        transform: None,
        // We do not require any particular HTTP headers in this example.
        headers: request_headers,
    };

    // 2. Execute the HTTP request. A request consumes Cycles(!). In this example we provide 2_000_000_000 Cycles (= 0.002 TCycles).
    // To estimate the costs see documentation:
    // - https://internetcomputer.org/docs/current/developer-docs/gas-cost#special-features
    // - https://internetcomputer.org/docs/current/developer-docs/integrations/https-outcalls/https-outcalls-how-it-works#pricing
    // Total amount of cycles depends on the subnet size. Therefore, on mainnet it might cost ~13x more than what's required when developing locally. Source: https://forum.dfinity.org/t/http-outcalls-cycles/27439/4
    // Note: In the future we will have a UI logging panel in console.juno.build to help debug on production. Follow PR https://github.com/junobuild/juno/issues/415.
    //
    // We rename ic_cdk::api::management_canister::http_request::http_request to http_request_outcall because the Satellite already includes such a function's name.
    match http_request_outcall(request, 2_000_000_000).await {
        Ok((response,)) => {
            // 3. Use serde_json to transform the response to a structured object.
            let str_body = String::from_utf8(response.body)
                .expect("Transformed response is not UTF-8 encoded.");

            let dog_response: DogApiResponse =
                serde_json::from_str(&str_body).map_err(|e| e.to_string())?;

            // 4. Our goal is to update the document in the Datastore with an update that contains the link to the image fetched from the API we just called.
            let dog: DogData = DogData {
                src: Some(dog_response.message),
            };

            // 5. We encode those data back to blob because the Datastore holds data as blob.
            let encode_data = encode_doc_data(&dog)?;

            // 6. Then we construct the parameters required to call the function that save the data in the Datastore.
            let doc: SetDoc = SetDoc {
                data: encode_data,
                description: context.data.data.after.description,
                updated_at: Some(context.data.data.after.updated_at),
            };

            // 7. We store the data in the Datastore for the same caller as the one who triggered the original on_set_doc, in the same collection with the same key as well.
            set_doc_store(
                context.caller,
                context.data.collection,
                context.data.key,
                doc,
            )?;

            Ok(())
        }
        Err((r, m)) => {
            let message =
                format!("The http_request resulted into error. RejectionCode: {r:?}, Error: {m}");

            Err(message)
        }
    }
}

This sample not only provides a practical demonstration of making HTTP outcalls but also illustrates the enhanced capabilities that serverless functions offer to developers using Juno.

Conclusion​

In conclusion, Juno's serverless functions mark a significant advancement in blockchain development, offering developers the tools to create more sophisticated and dynamic applications. This feature set not only broadens the scope of what can be achieved within Juno's ecosystem but also underscores the platform's commitment to innovation and developer empowerment. As we move forward, the potential for serverless technology in blockchain applications is boundless, promising exciting new possibilities for the future.

👋

Stay connected with Juno by following us on X/Twitter.

Reach out on Discord or OpenChat for any questions.

⭐️⭐️⭐️ stars are also much appreciated: visit the GitHub repo and show your support!