[haidrali]

I think AWS is good for side projects. I am also a solo developer and have deployed side projects on AWS so far my experience is very good. As you have mentioned that you can't afford to spend >100 euros/month I think you can go with AWS free tier where it is possible

1- For DB server you can you RDS free tier I would say it would be enough for a side project

2- For Redis Instance you can use EC2 free tier to run single Redis Instance or you can try Amazon elastic Cache as well

3- For Rails app depending upon your need again you can either use free tier server or whatever suits you check different AWS EC2 instance types https://aws.amazon.com/ec2/instance-types/

4- For CDN you have to use Amazon S3 first and that would cost you and cost depends upon usage + storage, since its a side project bill won't be too much

Happy Deployment ;)