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97 lines
3.0 KiB
97 lines
3.0 KiB
2 years ago
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#!/usr/bin/env python
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# This file implements the API shell.
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# You don't necessarily need to modify it for various algorithms.
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# It starts nginx and gunicorn with the correct configurations and
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# then waits until gunicorn exits.
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#
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# The flask server is specified to be the app object in wsgi.py
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#
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# We set the following parameters:
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#
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# Parameter Environment Variable Default Value
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# --------- -------------------- -------------
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# number of workers MODEL_SERVER_WORKERS the number of CPU cores
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# timeout MODEL_SERVER_TIMEOUT 60 seconds
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from __future__ import print_function
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import multiprocessing
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import os
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import signal
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import subprocess
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import sys
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cpu_count = multiprocessing.cpu_count()
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model_server_timeout = os.environ.get("MODEL_SERVER_TIMEOUT", 60)
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model_server_workers = int(os.environ.get("MODEL_SERVER_WORKERS", cpu_count))
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def sigterm_handler(nginx_pid, gunicorn_pid):
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try:
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os.kill(nginx_pid, signal.SIGQUIT)
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except OSError:
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pass
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try:
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os.kill(gunicorn_pid, signal.SIGTERM)
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except OSError:
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pass
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sys.exit(0)
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def start_server():
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print(f"Starting server with {model_server_workers} workers.")
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# link the log streams to stdout/err so that
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# they will be logged to the container logs
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subprocess.check_call(["ln", "-sf", "/dev/stdout", "/var/log/nginx/access.log"])
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subprocess.check_call(["ln", "-sf", "/dev/stderr", "/var/log/nginx/error.log"])
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nginx = subprocess.Popen(["nginx", "-c", "/opt/program/nginx.conf"])
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gunicorn = subprocess.Popen(
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[
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"gunicorn",
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"--timeout",
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str(model_server_timeout),
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"-k",
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"gevent",
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"-b",
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"unix:/tmp/gunicorn.sock",
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"-w",
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str(model_server_workers),
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"wsgi:app",
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]
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)
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# NOTE: https://docs.python.org/3/library/signal.html#signal.signal
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# This sets a handler (second argument) for the signal SIGTERM (first argument)
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# in the function `signal.signal` which we want to call (unclear why...)
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# The handler should be a callable which takes two arguments (hence `a`, `b`),
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# and it is called with two arguments: the signal number and current stack frame.
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# Neither of these are relevant to us, so we define a dummy handler which kills
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# the two processes we have started (nginx and gunicorn) regardless of `a`/`b`.
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# Basically, we are hard-coding "kill these two processes if you get a SIGTERM"
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def handler(a, b, c):
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return sigterm_handler(nginx.pid, gunicorn.pid)
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signal.signal(signal.SIGTERM, handler)
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# If either subprocess exits, so do we.
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pids = set([nginx.pid, gunicorn.pid])
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while True:
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pid, _ = os.wait()
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if pid in pids:
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break
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sigterm_handler(nginx.pid, gunicorn.pid)
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print("API server exiting")
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# The main routine just invokes the start function.
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if __name__ == "__main__":
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start_server()
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