Initialization and Provisioning

Initialization

Initialization is just a single script which registers blog.service and related blog.timer.

systemd is a system and service manager for Linux operating systems. When run as first process on boot (as PID 1), it acts as init system that brings up and maintains userspace services.

You can consider it as a program that wakes up periodically and does some job. The only reason I am using it is because smallest period in CRON Tabs is 1 minute.

If you open init-infra.sh, you will notice that all blog.service does is running /home/nurlashko/provision/run.sh and then deleting it once operation succeeds.

Provisioning

Another important task of init-infra.sh is starting latest provisioner microservice.

This part is quite tricky, hope you are still with me up until now.

Provisioner microservice starts with /home/nurlashko/provision/ folder mounted to its WORKDIR.

1. Provisioner copies his run.sh into mounted directory which pushes this file to a host filesystem.
2. On the host filesystem, blog.service eventually finds this file and executes it.
3. If provisioning finishes with success, blog.service deletes this file, which prevents it from keep re-provisioning it indefinitely.

In other words, provisioner microservice here is being used as a package delivery task.

This workflow especially powerful when combined with Watcher microservice.

Watcher pulls new version and restarts microservice once new version is available. You guessed it. Once there are any changes in the provisioning scripts(new microservice, config, etc.), changes will be pulled and re-provisioned accordingly.