85 lines
2.2 KiB
Markdown
85 lines
2.2 KiB
Markdown
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---
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layout: post
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title: "CGI-Like python scripts with systemd socket activation"
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date: 2015-06-25 10:52:19 +0200
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comments: true
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categories: systemd python
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---
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Lets say you want to trigger remote the start of a python script.
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But you don't want to have a service running all the time waiting for requests.
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What you can do, is using socket-unit in systemd, which is waiting on a tcp port for connections
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and starts the service, if somebody is requesting it.
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The systemd configuration could look like this:
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- Listens on tcp port 3000 (both ipv4 and ipv6)
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- Execute python script as user 'nobody' with a timeout of 5 minutes
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```
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[Unit]
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Description=Start update on demand
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[Socket]
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ListenStream=3000
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# only listen on localhost
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#ListenStream=127.0.0.1:3000
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BindIPv6Only=both
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[Install]
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WantedBy=multi-user.target
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```
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```
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[Unit]
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Description=Start update on demand
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JobTimeoutSec=5min
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[Service]
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User=nobody
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ExecStart=/usr/bin/python /path/to/script.py
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```
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In your python code, do the following
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```python
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def systemd_socket_response():
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"""
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Accepts every connection of the listen socket provided by systemd, send the
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HTTP Response 'OK' back.
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"""
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try:
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from systemd.daemon import listen_fds;
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fds = listen_fds()
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except ImportError:
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fds = [3]
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for fd in fds:
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import socket
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sock = socket.fromfd(fd, socket.AF_INET, socket.SOCK_STREAM)
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sock.settimeout(0)
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try:
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while True:
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conn, addr = sock.accept()
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conn.sendall(b"HTTP/1.1 200 OK\r\nContent-Type: text/plain\r\nContent-Length: 3\r\n\r\nOK\n")
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except socket.timeout:
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pass
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except OSError as e:
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# Connection closed again? Don't care, we just do our job.
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print(e)
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if __name__ == "__main__":
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if os.environ.get("LISTEN_FDS", None) != None:
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systemd_socket_response()
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# here your own code begins
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do_work()
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```
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This still lacks of authentication and does not take any arguments.
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You could protect this port using a frontend webserver with http authentication,
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or you pass the listen socket to an python http server, which add some token
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passed authentication. Systemd will ensure, that your service will not run more
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than once at the time.
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