Lifecycle
Understand the full journey of Serverless Functions in Juno, from setup and development to deployment and maintenance.
Initial Setup
If you didn’t use a template or skipped the language selection during setup, you can run juno dev eject at the root of your project. This command configures your project with the appropriate setup based on your language of choice. For Rust, it includes a Cargo.toml and a lib.rs file. For TypeScript, it sets up an index.ts file.
Developing Functions
Once your project is scaffolded, you can start writing your functions. Use the CLI to build them with:
juno dev build
If you start the emulator (see chapter below) in watch mode, your functions will be rebuilt automatically on save, so you don’t need to run this command manually.
Local Development
For local development and testing, a sandbox environment is essential. With Docker and the CLI, you can establish this environment by running juno dev start.
Find more information about local development in the documentation.
The local sandbox environment supports hot reloading. This means that the container will automatically redeploy your local Satellite each time juno dev build is executed and a new version is produced.
If you start the emulator with the --watch flag, it will also rebuild your functions automatically when changes are detected.
Deployment
After finalizing and testing your Functions, the next step is to deploy your modified Satellite to production. The juno dev build command produces a compressed WASM file (satellite.wasm.gz) that includes both the optimized code and necessary metadata. This file is located at ./target/deploy/satellite.wasm.gz relative to your project's root directory.
To deploy, use the following command from the same root directory:
juno upgrade -t s -s target/deploy/satellite.wasm.gz
This process updates your Satellite with your new custom Functions.
Summary
| CLI Command | Short description |
|---|---|
juno dev eject | Initializes your project for writing serverless functions. |
juno dev start | Starts the local development environment using Docker. |
juno dev build | Compiles your custom Satellite's code. Changes are automatically redeployed locally. |
juno upgrade -t s -s ./target/deploy/satellite.wasm.gz | Upgrades your Satellite in production. |