Timer Trigger¶

Timer-triggered functions run on a schedule instead of in response to external traffic. They are a good fit for maintenance jobs, polling loops, and lightweight recurring automation where NCRONTAB precision matters more than low-latency event delivery.

Trigger¶

Use @app.timer_trigger(...) with an NCRONTAB schedule.

Key parameters: schedule, arg_name, run_on_startup, and use_monitor.

import datetime
import azure.functions as func

app = func.FunctionApp()

@app.timer_trigger(schedule="0 */5 * * * *", arg_name="timer", run_on_startup=False, use_monitor=True)
def timer_example(timer: func.TimerRequest) -> None:
    if timer.past_due:
        print("Timer is running late")
    print(f"Ran at {datetime.datetime.utcnow().isoformat()}Z")

Input Binding¶

Timer has no native input payload, but it composes well with lookup bindings.

import azure.functions as func

app = func.FunctionApp()

@app.timer_trigger(schedule="0 0 * * * *", arg_name="timer")
@app.blob_input(arg_name="config", path="app-config/daily.json", connection="AzureWebJobsStorage")
def load_schedule_config(timer: func.TimerRequest, config: bytes) -> None:
    print(config.decode("utf-8"))

Output Binding¶

Timers commonly publish work to another system.

import json
import azure.functions as func

app = func.FunctionApp()

@app.timer_trigger(schedule="0 */15 * * * *", arg_name="timer")
@app.queue_output(arg_name="out_msg", queue_name="maintenance-jobs", connection="AzureWebJobsStorage")
def enqueue_maintenance(timer: func.TimerRequest, out_msg: func.Out[str]) -> None:
    out_msg.set(json.dumps({"job": "cleanup", "past_due": timer.past_due}))

Configuration¶

host.json usually only needs the extension bundle; timer-specific persistence is handled by the runtime monitor:

{
  "version": "2.0"
}

local.settings.json commonly needs AzureWebJobsStorage because schedule monitoring uses the storage account. If you reference app settings in the NCRONTAB string, add those keys too.

Scaling Behavior¶

A timer schedule is coordinated so one host instance claims each occurrence when monitoring is enabled. Timers do not scale out the way queues or hubs do; instead, one due occurrence becomes one invocation. Missed occurrences can replay as past_due after restarts depending on monitor state.

Common Pitfalls¶

use_monitor=False can skip persisted schedule tracking and is usually wrong for production jobs.
NCRONTAB has six fields in Azure Functions, including seconds.
Timer functions are poor choices for high-throughput parallel fan-out unless they immediately hand work to queues, hubs, or Durable Functions.

https://learn.microsoft.com/azure/azure-functions/functions-bindings-timer?pivots=programming-language-python&tabs=python-v2
https://learn.microsoft.com/azure/azure-functions/functions-bindings-timer#ncrontab-expressions