Drift · Driftfile: Atomic

Atomic functions

The atomic section sets the function runtime limits. You usually don't list functions at all: drop your handlers into atomic/ as flat source files and the CLI auto-discovers every @atomic function (that flat set is the default element, one language, one backend). A function's URL, method, and authentication come from a one-line directive at the top of its source, never from here:

# @atomic http=post:submit auth=none           # an HTTP endpoint
# @atomic http=get:status/:token auth=none     # with a path parameter
# @atomic queue=validate auth=none             # triggered by a queue message

The limits below apply to every function in the slice. There is no per-function override.

TypeDefaultMeaning

function_memory
Type
size (MB/GB)
Default
32MB
Meaning
Max memory per invocation; exceed it and the invocation is OOM-killed. Bounded to 32MB–256MB, and the resolved value is what you're billed.
atomic_size
Type
size (KB/MB/GB)
Default
platform default
Meaning
Total disk across all deployed functions: their code and the dependencies they vendor, which in practice is your dependency tree. A deploy that would exceed it is refused. Billed as the Atomic storage line.
function_timeout
Type
duration (s/m/h)
Default
platform default
Meaning
Max wall-clock time per invocation before it's killed.
rate_limit
Type
rate (N/s, N/min, N/h)
Default
platform default
Meaning
Max invocations across the whole slice per window. Excess requests get 429.
deploy_history
Type
integer
Default
platform default
Meaning
How many past deploys are kept per function for rollback (drift atomic rollback). Higher means more restore points, more storage.
egress
Type
map
Default
{ mode: open }
Meaning
Outbound network posture; see Outbound egress.
functions[]
Type
string | map (optional)
Default
auto-discovered
Meaning
Usually omitted, because functions are discovered from your flat atomic/* source. Long form adds a directory, an element, a schedule, or alerts; see below.

function_memory is bounded, not free-form.

A value outside 32MB–256MB is refused at create and at resize with function_memory must be between 32MB and 256MB. The ceiling is not a runtime limit in disguise: a compiled language's own startup floor is a platform-owned allowance added underneath, never billed, so the number here is your function's working set and nothing else.

The `functions[]` long form

A bare string is a function name. The map form carries four more keys, and two of them, cron and alerts, are the only way to put a function on a schedule or under an alert from the manifest.

TypeDefaultMeaning

name
Type
string
Default
required
Meaning
The function name. Standard identifier shape.
dir
Type
path
Default
./atomic/<name>
Meaning
Source directory, relative to the Driftfile.
element
Type
string
Default
the flat element
Meaning
The sub-app this function belongs to: the group that shares one language, one dependency manifest, one runtime.
cron
Type
5-field cron
Default
none
Meaning
Run this function on a schedule. The deploy ships a schedule trigger alongside its HTTP route.
alerts[]
Type
list of maps
Default
none
Meaning
Fire a notification when this function errors. Reconciled against the live alert registry on every deploy.

Driftfile

functions:
    - nightly-digest                     # bare name, nothing special
    - name: reconcile
      element: billing                   # lives with the other billing functions
      cron: "0 3 * * *"                  # 03:00 daily, 5 POSIX fields
      alerts:
        - on: errors                     # errors is the only accepted trigger
          threshold: 5                   # errors within the window
          window: 5m                     # minimum 60s
          notify: webhook=https://hooks.example.com/drift

cron is a 5-field POSIX expression; the parser checks the field count and the scheduler validates the grammar, so a malformed expression surfaces at deploy. An alert needs window and notify, and both are errors if missing. threshold defaults to 1, on to errors, and window must be at least 60 seconds. The only notify form is webhook=<http(s) URL>.

The reconcile runs both ways: the deploy deletes any live alert the manifest does not declare, so removing an alert from the Driftfile removes it from the slice.

Outbound egress

atomic.egress declares which hosts your functions may reach. It is the source of truth for the allowlist; drift atomic egress list/refresh/test inspect what the slice has, and there is no CLI verb to add a host.

Driftfile

atomic:
    egress:
      mode: allowlist                  # open (default) | allowlist
      hosts:
        - api.stripe.com
        - "*.amazonaws.com"            # accepted, then skipped: name concrete hosts
        - smtp.sendgrid.net:587        # host:port; port defaults to 443

An allowlist is declared, not yet enforced.

The deploy prints that in as many words when it applies one. Treat the block as a statement of intended reach and keep whatever authentication and secret hygiene you would have used without it. Private ranges are a separate matter and are blocked: RFC-1918, link-local and CGNAT egress is refused from a slice whatever mode says.

Read the Atomic guide → for how to write a function.

Atomic functions

The functions[] long form

Outbound egress

The `functions[]` long form