slack_notification

Post messages to Slack using an incoming webhook URL.

Parameters

Either text/message or payload.text is required.

webhook_url is optional and may be omitted if SLACK_WEBHOOK is set in env.

If payload is provided, all string values are context-interpolated (${ctx.key}).

HTTP Transport

Webhook redirects follow only the original scheme, host, and effective port, with at most 10 hops. Cross-origin redirects fail before replaying notification content. Automatic Referer is disabled so the token-bearing webhook path is not copied into that header. Configure a new webhook URL explicitly when its origin changes.

Success and error response bodies share the HTTP limit IRONFLOW_MAX_HTTP_BODY_BYTES (default 52428800, 50 MiB). An oversized Content-Length is rejected before reading the body; actual bytes are checked before each chunk is retained, including responses without a declared length. Exceeding the cap, a body-read failure, timeout, or run cancellation fails or cancels the step without publishing partial notification output. The cap applies to received body bytes before text decoding, not total process memory or decoded JSON size. Charset/BOM decoding and JSON-or-text output behavior are unchanged.

Non-2xx responses within the cap still fail with their status and redacted body detail. A size error takes precedence over provider body parsing when the cap is exceeded. A failed response read does not prove the message was not delivered; retrying a notification can send it again.

Context Output

• {output_key}_status — HTTP status code.
• {output_key}_data — Response body (JSON parsed if possible, otherwise raw text).
• {output_key}_success — true on HTTP 2xx success.

Example

The runnable Slack example uses SLACK_WEBHOOK, which can point to a local HTTP fixture for offline testing.

local flow = Flow.new("slack_notification")

flow:step("notify", nodes.slack_notification({
    webhook_url = env("SLACK_WEBHOOK"),
    text = "Workflow completed",
    payload = {
        username = "IronFlow",
        channel = "#alerts"
    }
})):depends_on("run_job")

flow:step("log", nodes.log({
    message = "Slack status: ${ctx.slack_status}"
})):depends_on("notify")

return flow