Capturing the data
My scenario is that I wish capture some multicast data and analyse it later. I’d like this process to be automated, start at a specific time, stop at a specific time, and then process the captured data file.
Fortunately, the ExaNIC cards come with a great utility called exanic-capture, this tool is one of the features of the ExaNIC card outlined in this post on the Exablaze site. The exanic-capture utility can produce a pcap file that has nanosecond timestamp resolution (6.2 nanoseconds).
systemd has the capability to create services and associated timers, in this case I wanted to capture mulitcast data between the hours of 0830 and 1700. I first created a mulitcast listener service that registers the host to listen for the data, and then a bit later I start a service to capture the raw data. Note I did not filter the data as I also wanted the data to be passed up to the kernel. If you add a filter to the exanic-capture utility it keeps the data to itself.
For the services on CentOS 7 I will define them under
[Unit] Description=Multicast Data listener After=NetworkManager.service Requires=NetworkManager.service [Service] TimeoutStartSec=0 ExecStart=/usr/bin/socat UDP4-RECVFROM:30011,ip-add-membership=126.96.36.199:10.3.78.13,fork - Restart=on-abort [Install] WantedBy=multi-user.target
[Unit] Description=Start registering for multicast data [Timer] OnCalendar=Mon-Fri *-*-* 08:00:00 Unit=mdlisten.service [Install] WantedBy=basic.target
Multicast data capture service
I called this service datacapture.service
[Unit] Description=Multicast Data collector After=mdlisten.service Requires=mdlisten.service [Service] TimeoutStartSec=0 ExecStart=/bin/sh -c "export D=\"`date +\"%Y%%m%%d\"`\"; /usr/bin/exanic-capture -i exanic0:0 -w /data/logging/$(hostname -s)/\"$D\".pcap " ExecStop=/bin/sh -c "export D=\"`date +\"%Y%%m%%d\"`\"; cd /data/logging/$(hostname -s)/;/usr/local/bin/process-data.sh \"$D\".pcap \"$D\"" #Restart=on-abort [Install] WantedBy=multi-user.target
Multicast data capture timer
I have this setup to start 5 minutes after the listener
[Unit] Description=Start listening to market data [Timer] OnCalendar=Mon-Fri *-*-* 08:05:00 Unit=datacapture.service [Install] WantedBy=basic.target
Clock sync service
This service is going to run all the time, and requires that NTP service is running
[Unit] Description=ExaNIC Clock Sync to host After=ntpd.service Requires=ntpd.service [Service] TimeoutStartSec=0 ExecStart=/usr/bin/exanic-clock-sync exanic0:host Restart=on-abort [Install] WantedBy=multi-user.target
systemctl daemon-reload systemctl status mdlisten systemctl status mdlisten.timer
You will see that both services are disabled by default, we will need to enable each of new services
systemctl enable mdlisten systemctl enable mdlisten.timer systemctl enable market systemctl enable datacapture.timer systemctl enable datacapture
Then ensure that the status is correct for each service and that the timers fire their respective services at the correct times.