Runtimes

Polyglot Serverless

Write functions in your preferred language. Seven verified runtimes — every function runs isolated in its own Firecracker micro-VM.

Verified Runtimes

python
Python 3.x

pip packages installed automatically during the build. Great for ML/AI workloads.

js
JavaScript / Node.js Node LTS

npm packages installed during the build.

php
PHP 8.x

composer packages installed during the build.

ruby
Ruby stable

gem packages supported.

go
Go stable

Single binary deployment. Excellent performance.

java
Java / JVM JVM 21

JAR-based deployment (fat jar). Full Java ecosystem.

binary
Binary (any) any

Ship an executable in an archive — shell scripts, Go binaries, anything.

Custom Runtime Images

docker
Docker (any language) any

Bring your own Fission-compatible runtime image (publicly pullable, HTTP server on port 8888). Haskell, Deno, Ballerina, etc.

Same Function, Multiple Languages

hello.py
from flask import request

def main():
  return {"status": 200,
    "body": "Hello, "
      + (request.args.get(
          "name") or "World")}
hello.php
<?php
$name = $_GET['name']
  ?? 'World';
echo "Hello, $name";
hello.rb
def main(params)
  name = params["name"]
    || "World"
  "Hello, #{name}"
end

Deployment Options

1 · Single file

Paste your code directly into the create call — no build step. Perfect for getting started.

2 · Archive URL + builder

Host an archive (CI, GitHub release). The builder installs pip/npm/composer packages automatically. Set the entrypoint as "module.function", e.g. "hello.main".

3 · OCI image

Deploy code from a container image your CI already builds — no archive, no builder.