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Getting started with Momento Functions

This page walks you from a fresh machine to a deployed Function in a few minutes. By the end you'll have a pong web Function running on the Momento platform that you can curl. From there, the rest of the Develop section shows you how to add JSON, headers, cache reads, and other stuff.

One-time setup​

Functions are written in Rust and compiled to wasm32-wasip2. You need a Rust toolchain and the matching target.

# Install Rust
# https://rustup.rs/
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

# Add the Functions compile target
rustup target add wasm32-wasip2

You also need a Momento API key for the cache that will host your Function. If you don't have one, follow the authentication guide.

Create a project​

Functions are ordinary Rust libraries that compile to a WebAssembly artifact.

cargo init --lib hello
cd hello

Set the build target​

Add .cargo/config.toml so you don't have to pass --target on every build:

[build]
target = "wasm32-wasip2"

Configure Cargo.toml​

A minimal web Function needs the bytes host crate (for payloads) and guest-web host crate (for the invoke! macro). Tell cargo to produce a cdylib to get the right .wasm output:

[lib]
crate-type = ["cdylib"]

[dependencies]
momento-functions-bytes     = { version = "0" }
momento-functions-guest-web = { version = "0" }

Write the Function​

Fill src/lib.rs with the simple web Function (of course you don't have to write this in lib.rs, but it makes the example slightly shorter so here we are):

use momento_functions_bytes::Data;
use momento_functions_guest_web::invoke;

invoke!(ping);
fn ping(_payload: Data) -> &'static str {
    "pong"
}

Data is a handle on a host-side buffer — the bytes don't need to enter your sandbox unless you call Data::into_bytes(). The invoke! macro wires ping up as the entry point the Function host calls.

Build​

cargo build --release

Your artifact is at target/wasm32-wasip2/release/hello.wasm.

Deploy​

You can deploy with the Momento CLI (recommended) or by base64-encoding the artifact and uploading it directly to the management API.

momento preview function put-function \
   --cache-name "$MOMENTO_CACHE_NAME" \
   --name ping \
   --wasm-file target/wasm32-wasip2/release/hello.wasm

In the placeholders above:

  • MOMENTO_CACHE_NAME - The cache that hosts the Function. Functions are scoped to a cache.
  • MOMENTO_CELL_HOSTNAME - The region endpoint for your cache.
  • MOMENTO_API_KEY - A Momento API key with permission to manage Functions.

Invoke​

Functions are callable over HTTP at the same endpoint as the cache that hosts them.

curl \
  https://api.cache.$MOMENTO_CELL_HOSTNAME/functions/$MOMENTO_CACHE_NAME/ping \
  -H "authorization: $MOMENTO_API_KEY" \
  -d 'ping'

You should see pong.

tip

For more substantial starting points — JSON request/response, token vending, cache integration, HTTP fan-out to OpenAI and Turbopuffer — see the examples/ directory in the Functions repo.

Next steps​