[gunicorn] basic use of gunicorn

Gunicorn

gunicorn is a python-based Web Servers Gateway Interface for unix; it is a bridge between the web server receiving requests and the python app application;
if you don't use gunicorn, just use Flask, for a large number of simultaneous requests, it will crash and errors will occur; And gunicorn is for a large number of highly concurrent requests, can realize the request to reach the server, and make a response, and can increase/decrease the worker in time according to the load demand, so as to achieve the role of management coordination.

basic introduction

Gunicorn is a way to start the app program, which is different from starting the app program directly in the main file, which is more convenient and manageable;
three startup methods:

• workers mode

  Each worker is a UNIX process that loads the python application No shared memory between workers

  The recommended number of workers is (2*CPU) + 1;

• multi-threaded mode

  Gunicorn also allows each worker to have multiple threads. In this mode, each worker will be loaded once, and each thread generated by the same worker will share the same memory space. Use threads mode, use threads mode every time, worker class It will be gthread;

  gunicorn -w 5 --threads=2  main:app
  #等同于
  gunicorn -w 5 --thread=2 --worker-class=gthread main:app
  

• Pseudo-thread gevent (coroutine)

  gunicorn --worker-class=gevent --worker-connections=1000 -w 3 main:app
  

  work-connections is a special setting for the gevent worker class; the recommended number of workers is still (2*CPU) + 1;

  In this case, the maximum number of concurrent requests is 3000 (3 workers * 1000 connections/worker).

basic use

Start with a configuration file

gunicorn --config=config.py myapp.test:app
#myapp.test为文件，第二个指的是flask应用的名字；

close gunicorn

pstree -ap|grep gunicorn #寻找masterpid
kill -HUP 9479 #重启Gunicorn任务
kill -9 9479 #退出gunicorn任务

• gunicorn address used
  If you use gunicorn to start, you don't need to mianstart it, and you don't need to use it app.run();

#gunicorn 启动
if __name__ != '__main__':
	#日志的绑定
	gunicorn_logger = logging.getLogger(‘gunicorn.error’)#获得gunicorn的logger
	#将gunicorn的logger和flask app的logger绑定在一起
    app.logger.handlers = gunicorn_logger.handlers
    #将绑定的logger 的level设置成gunicorn logger的level, 因为最终输出的log level是在gunicorn中配置的
    app.logger.setLevel(gunicorn_logger.level)
    #启动分析任务
    crossline_t = threading.Thread(target=crossline_analyze.task_start)
    crossline_t.start()

• Exit gunicorn
  to end the process according to the pid number in the pid file

  kill -QUIT pid
  kill -TERM pid	
  

ref:

gunicorn configuration file
gunicorn documentation
Gunicorn introduction and pressure measurement
gunicorn log binding
reference 01
The role of the pid file

common mistakes

• No module named <module_name>" while running gunicorn
  Celery cannot be found in gunicorn. By checking, we which gunicorncan see that the default call is gunicorn under local; uninstall and reinstall gunicorn in the virtual environment where celery is installed;
  when using it, you need to specify the specific location of gunicorn in the virtual environment;
  if bad interpreteran error occurs , needs to be in progress bin/gunicorn, edit the python interpreter path in the first line;
  soft link the gunicorn in the virtual environment to the local path, then use without specifying the specific path;

• gunicorn.errors.HaltServer
--preloadAdd to display specific errors at startup ;