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run-and-update-service

Install sig as a long running service on a linux system, and periodically have it self-update based on the latest code in the configured branch and restart. This exists to maintain CI test environments.

Install​

git clone https://github.com/Syndica/sig.git
cd sig/ci/run-and-update-service

sudo make install      # install update script and systemd units to the system
sudo vim /etc/sig.conf # optionally edit file to specify custom configuration
sudo make start        # start sig, metrics, and the timer to periodically update sig

Uninstall​

sudo make uninstall

Configuration​

These options may be configured in /etc/sig.conf

  • CLI_ARGS: The command line options that will be passed to sig. Default: '--log-file /home/sig/sig/logs/sig.log'
  • BRANCH: The branch that will be checked periodically and rebuilt when it changes. Default: 'main'
  • SLACK_WEBHOOK_URL (optional): Enable slack web hooks. Only used if non-empty. Default: ''

Design​

The service is installed to the system in /usr/local using make. A new user called sig is added to the system and is used to build and run the sig binary.

The service is orchestrated by systemd, using two services and one timer.

Note: Systemd is the most common init system for linux. It can run processes, daemons, and schedules. A service is a short- or long-running process that's run by systemd, and a timer is used to start services on a schedule, similar to a cron job.

Call graph: sig-update.timer -> sig-update.service -> sig-update -> sig.service -> sig

sig-update.timer periodically runs the sig-update binary as root on a schedule. This script de-escalates to the sig user to check if there are new commits on BRANCH, and if so, it builds a new sig binary. Then as root, it restarts sig.service and starts sig's metrics with docker-compose. As the sig user, sig.service runs the sig binary that was built in the sig user's home folder, passing the configured CLI_ARGS.

Config​

The configuration file /etc/sig.conf is used by both systemd and the sig-update binary. systemd reads the file when running sig.service in order to pass the correct CLI_ARGS to sig. sig-update reads the file when it's checking the BRANCH for new commits, and when setting the SLACK_WEBHOOK_URL for sig's metrics.

Root privileges​

All of the systemd units are system-level units, with some root privileges, because we want the service to start reliably when the system boots. If these three units were instead user-level units, they would only run after the user logs in. Automating startup on boot would require additional system-level units to log in the user, which would increase the complexity. Minimal root privileges were integrated into the existing units to keep this both simple and reliable.