Functions module

Work in progress

Functions are a work in progress: the API, the interface and the CLI exist, but the feature can still change. Runtime updates, external secret stores, public HTTP access and a per-function disk quota are not available yet.

The Functions module runs handlers written for AWS Lambda™ (Node.js, Python, or a compiled bootstrap) on the Docker host, in the AWS Lambda base images published by AWS, with Loch Lambda Runtime as entrypoint. This page sets the module up. To create and run functions, see Functions.

note

Admin only. Requires FUNCTIONS_ENABLED=true and HOSTING_STACKS_DIRECTORY (the compose files go there, even when the Hosting module is off).

Enable the module

Add the variables to the API .env, then restart the API:

Variable	Role	Default
FUNCTIONS_ENABLED	Enables the module	false
FUNCTIONS_DATA_DIRECTORY	Code, runtime binaries, secrets and references. Same path on the host and in the API container	/data/functions
FUNCTIONS_RUNTIME_DOWNLOAD	Download the runtime binary from GitHub when it is missing	true
FUNCTIONS_RUNTIME_SOURCE_DIR	Directory holding the runtime binary, for offline installations	empty

FUNCTIONS_DATA_DIRECTORY takes letters, digits and _ . / - only. It must be outside HOSTING_STACKS_DIRECTORY, HOSTING_SITES_DIRECTORY, SFTP_DIRECTORY, SERVICES_DATA_DIRECTORY and API_LOG_DIR. A subdirectory of DATA_DIR is fine, DATA_DIR itself is not. The API checks it at startup. Every directory under it must be owned by the panel and writable by nobody else.

The menu Serverless → Functions appears for admins. If the installation checks fail (directories, Docker), only the module is disabled: the API logs say why, and GET /functions/config answers FUNCTIONS_MISCONFIGURED.

Limits and budgets: Configuration reference.

Runtime binary

Every function runs the Loch Lambda Runtime binary. The panel build trusts given releases (today v1.0.1, amd64 and arm64) and only stores a binary that matches their size and SHA-256.

Mode	How
Download (default)	At startup, the panel downloads the release for the host architecture from GitHub over HTTPS. Allow outbound HTTPS to github.com, release-assets.githubusercontent.com and objects.githubusercontent.com. HTTPS_PROXY is honored
Offline	Set FUNCTIONS_RUNTIME_DOWNLOAD=false and FUNCTIONS_RUNTIME_SOURCE_DIR to a directory holding loch-lambda-runtime-linux-<arch>, mounted read-only in the API container

# On a machine with Internet access, then copy the files to the host
gh release download v1.0.1 -R loch-sh/lambda-runtime -p 'loch-lambda-runtime-linux-*' -p 'SHA256SUMS*'
shasum -a 256 -c SHA256SUMS --ignore-missing

The source directory and its files must be owned by the panel's user or root and writable by nobody else, as regular files (no symlinks). Otherwise the API refuses to start.

While no trusted binary is installed, the list page says No trusted function runtime is installed on the server yet, and creating or starting a function fails with FUNCTION_RUNTIME_UNAVAILABLE: the reason is in the API logs. An installed binary is never replaced. One that fails verification must be removed by hand. Release verification: Releases.

What the panel creates

Object	Name
Compose project	fn-<name> in HOSTING_STACKS_DIRECTORY. It starts with docker compose up -d without the panel
Private network	fn-<name>, created with the function
Image	mirror.gcr.io/amazon/aws-lambda-nodejs, …-python or …-provided, pinned by digest
Code	Read-only deployments in FUNCTIONS_DATA_DIRECTORY, mounted at /var/task
Secrets	A file of the private directory, never in compose.yaml

A compose file edited by hand is never run again: the function shows Edited outside the panel and can only be purged.

Networks and egress

• A function never joins the services network. It joins its own network fn-<name> and the private networks you attach.
• It has no published port. Members of its networks reach it on port 8080, with its invoke credentials.
• Internet access is off by default. When on, the function also reaches the host gateway, the LAN and cloud metadata endpoints unless DOCKER-USER firewall rules block them. Turning it on is audited as a warning.
• Function containers are protected like the API container: no shell, file copy, file tail, port tunnel, container action or exec scheduled task. Their stdout logs stay readable by admins. Restricted users never see them, and fn-* containers cannot be granted.

API key scopes

Scope	Allows
functions:read	Read functions and the module configuration
functions:write	Create, resize, start, stop, restart, delete
functions:deploy	Code, deployments, secrets, credentials, variables, handler, networks, egress, MCP opt-in
functions:invoke	Invoke. Implied by no other scope but *

The interface does not offer these scopes in its key form yet: use a key with All permissions, or create one through the API. Details: API key scopes.

Audit

Every change is audited (function created, function code deployed, function secret set with the name only, function egress toggled…). Invocations are counted per function and per minute in function invoked, never with their content. Full list: Audit trail.

Good to know

• The total memory and CPU of all functions are capped by FUNCTIONS_MAX_TOTAL_MEMORY and FUNCTIONS_MAX_TOTAL_CPUS (default: the host memory and 4 × its CPUs).
• The kept deployments bound the disk used per function: FUNCTIONS_DEPLOYMENTS_KEPT × 250 MB at most.
• Deleting the compose directory does not delete the code or the secrets.
• At startup, the panel removes interrupted uploads and logs the functions edited outside the panel.
• AWS and AWS Lambda are trademarks of Amazon.com, Inc. or its affiliates. Loch.sh is not affiliated with or endorsed by Amazon.