example.py

from airflow import DAG
from airflow.operators.bash_operator import BashOperator
from datetime import datetime, timedelta

default_args = {
    'owner': 'airflow',
    'depends_on_past': False,
    'start_date': datetime(2018, 1, 1),
    'email_on_failure': False,
    'email_on_retry': False,
    'retries': 1,
    'retry_delay': timedelta(minutes=5),
}

dag = DAG('example_dag',
          max_active_runs=50,
          concurrency=500,
          schedule_interval=timedelta(minutes=5),
          default_args=default_args)

t1 = BashOperator(
    task_id='print_date1',
    bash_command='true',
    #bash_command='sleep $[ ( $RANDOM % 30 )  + 1 ]s',
    dag=dag)

t2 = BashOperator(
    task_id='print_date2',
    bash_command='true',
    dag=dag)

t3 = BashOperator(
    task_id='print_date3',
    bash_command='true',
    dag=dag)

t4 = BashOperator(
    task_id='print_date4',
    bash_command='true',
    dag=dag)

t5 = BashOperator(
    task_id='print_date5',
    bash_command='true',
    dag=dag)

t6 = BashOperator(
    task_id='print_date6',
    bash_command='true',
    dag=dag)

t7 = BashOperator(
    task_id='print_date7',
    bash_command='true',
    dag=dag)

t8 = BashOperator(
    task_id='print_date8',
    bash_command='true',
    dag=dag)

t2.set_upstream(t1)
t3.set_upstream(t2)
t4.set_upstream(t3)
t5.set_upstream(t3)
t6.set_upstream(t3)
t7.set_upstream(t3)
t8.set_upstream(t3)

t9 = BashOperator(
    task_id='print_date9',
    bash_command='true',
    dag=dag)

t10 = BashOperator(
    task_id='print_date10',
    bash_command='true',
    dag=dag)

t11 = BashOperator(
    task_id='print_date11',
    bash_command='true',
    dag=dag)

t12 = BashOperator(
    task_id='print_date12',
    bash_command='true',
    dag=dag)

t9.set_upstream(t8)
t10.set_upstream(t8)
t11.set_upstream(t8)
t12.set_upstream(t8)