Heroku is awesome for this use case, but there are also great alternatives based on Cloud Foundry. Cloud Foundry is an open source PaaS with support for Heroku buildpacks + docker containers. At a median of ~5€/GB RAM per month they will also be a bit cheaper than Heroku.

Some providers that offer Cloud Foundry including a free tier for small Apps:

- Meshcloud (hosted in Germany, 2 Locations) https://panel.meshcloud.io/#/register (Disclaimer: I'm a founder there)

- Pivotal Web Services (hosted on AWS US): https://run.pivotal.io/

- IBM Bluemix https://www.ibm.com/cloud-computing/bluemix/ (various locations, a bit more expensive than the other two though)