Environment Variables¶

Verified status as of March 28, 2026.

This page is a practical index of the environment variables that show up most often in FastFN docs and runtime behavior.

Quick View¶

Complexity: Reference
Typical time: 10-15 minutes
Use this when: you want to know which FN_* variables matter and what each one does
Outcome: you can set the right variable in the right place without guessing

Variable	Default	What it controls
`FN_HOST_PORT`	`8080`	HTTP listen port for the gateway
`FN_FUNCTIONS_ROOT`	project-specific	Root directory for functions and discovery
`FN_RUNTIMES`	`python,node,php,lua`	Which runtimes are enabled. Rust and Go must be added explicitly (e.g. `FN_RUNTIMES=python,node,php,lua,rust,go`)
`FN_NAMESPACE_DEPTH`	`3`	How deep runtime-grouped discovery recurses
`FN_ZERO_CONFIG_IGNORE_DIRS`	empty	Extra directories ignored by zero-config discovery
`FN_FORCE_URL`	`0`	Global config route override behavior
`FN_PUBLIC_BASE_URL`	request-derived	Canonical OpenAPI server URL
`FN_OPENAPI_INCLUDE_INTERNAL`	`0`	Whether internal `/_fn/*` paths appear in OpenAPI
`FN_HOT_RELOAD`	`1`	Enables hot reload in `dev` and `run`

Variable	Default	What it controls
`FN_RUNTIME_DAEMONS`	one per runtime	Number of external runtime daemons to launch
`FN_RUNTIME_SOCKETS`	generated sockets	Explicit socket map for runtimes
`FN_SOCKET_BASE_DIR`	internal default	Base directory for generated socket paths
`FN_RUNTIME_LOG_FILE`	empty	File used for runtime log capture
`FN_MAX_FRAME_BYTES`	`2097152`	Maximum socket frame size accepted by runtimes
`FN_*_BIN`	runtime default	Host binary used by a specific runtime/tool

Common binary overrides:

Variable	Default	What it controls
`FN_STRICT_FS`	`1`	Handler filesystem sandboxing
`FN_STRICT_FS_ALLOW`	empty	Extra allowed roots for strict fs access
`FN_PREINSTALL_PY_DEPS_ON_START`	`1`	Preinstall Python deps before serving
`FN_AUTO_INFER_PY_DEPS`	`1`	Infer Python deps from imports
`FN_PY_INFER_BACKEND`	`native`	Python inference backend (`native`, `pipreqs`)
`FN_AUTO_INFER_WRITE_MANIFEST`	`1`	Write inferred dependency manifests
`FN_AUTO_INFER_STRICT`	`1`	Make dependency inference stricter
`FN_PY_RUNTIME_WORKER_POOL`	`1`	Enable Python persistent worker pool
`FN_GO_RUNTIME_WORKER_POOL`	`1`	Enable Go persistent worker pool
`FN_NODE_RUNTIME_PROCESS_POOL`	`1`	Enable Node persistent worker pool
`FN_NODE_INFER_BACKEND`	`native`	Node inference backend (`native`, `detective`, `require-analyzer`)

Variable	Default	What it controls
`FN_UI_ENABLED`	`0`	Console UI availability
`FN_CONSOLE_API_ENABLED`	`1`	Console API availability
`FN_CONSOLE_WRITE_ENABLED`	`0`	Console write operations
`FN_CONSOLE_LOCAL_ONLY`	`1`	Local-only access guard
`FN_ADMIN_TOKEN`	empty	Admin override token
`FN_CONSOLE_LOGIN_ENABLED`	`0`	Console UI login screen
`FN_CONSOLE_LOGIN_API`	`0`	Whether login also protects console API
`FN_CONSOLE_LOGIN_USERNAME`	empty	Login username
`FN_CONSOLE_LOGIN_PASSWORD_HASH`	empty	Recommended login hash (`pbkdf2-sha256:<iterations>:<salt_hex>:<digest_hex>`)
`FN_CONSOLE_LOGIN_PASSWORD_HASH_FILE`	empty	File that contains the login password hash
`FN_CONSOLE_LOGIN_PASSWORD`	empty	Legacy plaintext login password fallback
`FN_CONSOLE_LOGIN_PASSWORD_FILE`	empty	File that contains the legacy plaintext login password
`FN_CONSOLE_SESSION_SECRET`	empty	Signed session cookie secret
`FN_CONSOLE_SESSION_SECRET_FILE`	empty	File that contains the signed session secret
`FN_CONSOLE_SESSION_TTL_S`	`43200`	Session cookie lifetime
`FN_CONSOLE_LOGIN_RATE_LIMIT_MAX`	`5`	Maximum login attempts per window
`FN_CONSOLE_LOGIN_RATE_LIMIT_WINDOW_S`	`300`	Login rate-limit window in seconds
`FN_CONSOLE_RATE_LIMIT_MAX`	`120`	Max read/UI console requests per window
`FN_CONSOLE_RATE_LIMIT_WINDOW_S`	`60`	General console rate-limit window in seconds
`FN_CONSOLE_WRITE_RATE_LIMIT_MAX`	`30`	Max write/admin console requests per window

Variable	Default	What it controls
`FN_SCHEDULER_ENABLED`	`1`	Enable or disable the scheduler
`FN_SCHEDULER_INTERVAL`	`1`	Tick interval in seconds for checking due schedules
`FN_SCHEDULER_PERSIST_ENABLED`	`1`	Persist scheduler state to disk
`FN_SCHEDULER_PERSIST_INTERVAL`	`15`	How often (seconds) to write state to disk
`FN_SCHEDULER_STATE_PATH`	`<functions_root>/.fastfn/scheduler-state.json`	Path for scheduler state file
`FN_JOBS_ENABLED`	`1`	Enable or disable the async jobs queue
`FN_JOBS_POLL_INTERVAL`	`1`	Jobs queue polling interval in seconds
`FN_JOBS_MAX_CONCURRENCY`	`2`	Maximum concurrent job executions
`FN_JOBS_MAX_RESULT_BYTES`	`262144`	Maximum result storage per job (256 KB)
`FN_JOBS_DIR`	`/tmp/fastfn/jobs`	Directory for job spec and result files

Variable	Default	What it controls
`FN_RUST_BUILD_TIMEOUT_S`	`60`	Timeout for Rust handler compilation
`GO_BUILD_TIMEOUT_S`	`30`	Timeout for Go handler compilation

Variable	Default	What it controls
`FN_MAX_ASSET_BYTES`	`33554432`	Maximum asset size served from memory
`FN_HOT_RELOAD_WATCHDOG`	`0` or runtime default	File watcher mode for dev workflows
`FN_HOT_RELOAD_WATCHDOG_POLL`	runtime default	Watchdog poll interval
`FN_HOT_RELOAD_DEBOUNCE_MS`	runtime default	Debounce for reload events

Some variables are read by the CLI, some by the gateway, and some by runtime daemons.
The same FN_* prefix can mean different scopes depending on the file or service that reads it.
If a variable does nothing, check which process is actually reading it.
For console login, PBKDF2 is the recommended hash format; sha256:<hex> remains accepted only as a legacy compatibility format.
Dependency inference backends are optional. Explicit manifests stay faster and more predictable than invoking pipreqs, detective, or require-analyzer.

Last reviewed: March 28, 2026 · Docs on fastfn.dev