Functions

Deploy function bundles and expose them through gateway routes. HTTP and websocket $connect events carry gateway request headers, including X-Forwarded-For and X-Kernstack-Viewer-* location fields.

Declare a function

Add an entry under resources.functions[] in stack.json (omit src when source lives at functions/{name}), add a matching gateway.routes[] entry, then run kernstack deploy. See the IAC reference.

Workflow

1. Add a function: kernstack add function --name api (or edit stack.json).
2. Deploy: kernstack deploy (or kernstack deploy --only function:api).
3. Call the HTTP route URL from the deploy output.
4. Optionally add schedules under resources.functions[].schedules[].

Change stream events

A function named in a table's change_stream.function receives batched item changes. See change streams for delivery semantics and the record format.

func handler(ctx context.Context, req sdk_types_functions.FunctionInvokeRequest) (sdk_types_functions.FunctionInvokeResponse, error) {
    if req.IsChangeStreamEvent() {
        for _, rec := range req.ChangeRecords {
            switch rec.ChangeType {
            case "INSERT", "MODIFY":
                // rec.NewItem holds the item after the write; rec.OldItem is nil for new items
            case "REMOVE":
                // rec.OldItem holds the deleted item
            }
            _ = rec.Keys
        }
        return sdk_types_functions.FunctionInvokeResponse{StatusCode: 200}, nil
    }
    // ... HTTP, schedule and other triggers
}

req.ChangeTableName names the source table, so one function can serve several tables. Returning an error (or a 5xx or 429 response) retries the whole batch, and later changes wait until it succeeds or is 24 hours old. Other 4xx responses are not retried. A record can occasionally be delivered more than once, so make the handler idempotent; rec.ChangeID identifies each change.

CLI

Operation	Command
Add blueprint	kernstack add function [--name NAME]
Serve locally	kernstack serve [--function NAME]
Deploy	kernstack deploy
Scoped deploy	kernstack deploy --only function:NAME
Tail logs	kernstack logs --function NAME

kernstack add function --name api
kernstack deploy
kernstack serve --function api