Heroku is the managed PaaS that popularized git push heroku main as a deployment workflow. You point it at a repository, it detects the language via a buildpack, compiles a slug, and runs it inside a lightweight Linux container called a dyno. Everything — processes, scaling, logging, add-ons — is described through the Procfile and a handful of CLI commands.
The dyno model is the core abstraction: stateless, ephemeral containers that are restarted at least daily and assigned to a process type (web, worker, etc.). Scaling is horizontal (heroku ps:scale web=5) and vertical across predefined dyno sizes. Persistent state lives in managed add-ons — Heroku Postgres, Heroku Redis, Kafka — attached via config vars. Releases are immutable and rollbacks are a single command.
Heroku was acquired by Salesforce in 2010 and the buildpack spec it invented became the basis for Cloud Native Buildpacks, now used by Paketo, kpack, and pack. It ended its free tier in late 2022, which pushed many hobby users toward Fly.io, Render, and Railway, but it remains a reference point for what a good developer experience on top of a container platform looks like. If you have ever deployed to Kubernetes and thought “this should be one command,” you are thinking of Heroku.