Sometimes it is the best to create reminders for your annual events so that you don't forget and miss those special dates.
If you and your team/friends are using Slack, then it is a good idea that you automate these reminders via slackbots.
While doing so, if you want your slackbot to be a low maintenance one in that; it may be the best to use serverless technologies for concurrent interactions with the source, also enabling horizontal scalability.