Forked from kouk/Example health-check script with systemd socket activation
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April 18, 2018 12:56
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Simple HTTP health-check by abusing systemd socket activation with shell scripts
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| $ ./status.sh 3>&2 3<&0 | |
| GET / HTTP/1.1 | |
| Host: foo.bar.com | |
| HTTP/1.0 404 Not Found | |
| Content-Type: text/html | |
| Content-Length: 38 | |
| Date: Fri, 05 Dec 2014 17:06:53 +0000 | |
| Host: foo.bar.com | |
| <html> | |
| <body> | |
| <h1>WUT</h1> | |
| </html> | |
| </body> |
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| $ curl --dump-header - localhost:12345 | |
| HTTP/1.0 404 Not Found | |
| Content-Type: text/html | |
| Content-Length: 43 | |
| Date: Fri, 05 Dec 2014 17:48:56 +0000 | |
| <html> | |
| <body> | |
| <h1>WUT</h1> | |
| </html> | |
| </body> | |
| $ sudo systemctl start someservice | |
| $ curl --dump-header - localhost:12345 | |
| HTTP/1.0 200 OK | |
| Content-Type: text/html | |
| Content-Length: 43 | |
| Date: Fri, 05 Dec 2014 17:48:56 +0000 | |
| <html> | |
| <body> | |
| <h1>WUT</h1> | |
| </html> | |
| </body> | |
| $ |
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| #!/bin/sh | |
| # fd 3 is what systemd gave us | |
| while true ; do | |
| sed -e 's/\r$//' | IFS=":" read header line <&3 | |
| [ "$header" == "Host" ] && host="$header:$line" | |
| [ -z "$header" ] && break | |
| done | |
| if /path/to/somecommand >/dev/null 2>&1; then | |
| cat >&3 <<EOF | |
| HTTP/1.0 200 OK | |
| EOF | |
| else | |
| cat >&3 <<EOF | |
| HTTP/1.0 404 Not Found | |
| EOF | |
| fi | |
| cat >&3 <<EOF | |
| Content-Type: text/html | |
| Content-Length: 43 | |
| Date: $(date -R) | |
| EOF | |
| [ -n "$host" ] && echo $host | cat >&3 | |
| cat >&3 <<EOF | |
| <html> | |
| <body> | |
| <h1>WUT</h1> | |
| </html> | |
| </body> | |
| EOF |
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| [Unit] | |
| Description=Monitor Socket | |
| [Socket] | |
| ListenStream=12345 | |
| Backlog=1 | |
| MaxConnections=3 | |
| Accept=yes | |
| [Install] | |
| WantedBy=sockets.target |
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| [Unit] | |
| Description=monitor service | |
| Requires=status.socket | |
| After=syslog.target network.target | |
| [Service] | |
| Type=forking | |
| ExecStart=/path/to/status.sh | |
| [Install] | |
| WantedBy=multi-user.target | |
| Also=status.socket |
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An example of a health-check with systemd socket activation is when you run a small web app about thc infused seltzer that only starts when someone visits it. Systemd listens on a port, and when traffic comes, it automatically starts the service. The app includes a simple /health endpoint that returns “200 OK” to show it is working. This setup saves system resources and makes monitoring easy.