By Kane Hooper: Certified Heroku Architect and Salesforce AI Specialist.
Earlier this year reinteractive was involved in beta testing the Next Gen Heroku Fir platform. Since we have been utilising Heroku for close to 12 years it was a good opportunity to deploy a few major applications on the platform and see how it compares to the traditional Heroku build process.
The way in which Fir builds application has been completely re-achitected. Heroku slugs? Gone! Fir uses something called Cloud Native Buildpacks (CNBs) which generates standard OCI container images – basically, the kind of container images Docker uses. This makes a big difference as it means your builds are uniquely tied to the Heroku platform. You could potentially build on Fir and run that same image locally, say in Docker, or on another cloud platform which gives you a lot of versatility. That’s a big win for flexibility and avoiding vendor lock-in. It appears that builds are faster too, especially for updates, because of smarter caching. We'll have to see how that pans out in practice for hefty Rails apps with lots of gems, but the potential is there. If you were relying on custom classic buildpacks on Cedar though, be prepared to rewrite them for the CNB way of doing things.
One of the elements our team is very happy with is the expanded range of dynos. Instead of the handful of types on the traditional Heroku platofm, Fir launched with 18 different options, with more granular steps in CPU and memory. You can pick a dyno size that actually fits your web process or your Sidekiq worker, instead of just jumping to the next big tier and paying for resources you don't need. Right-sizing could genuinely save some cash and maybe even boost performance. Plus, the overall limits – dynos per app, apps per space – are much higher, which is good news if you're running lots of services or really large applications.
However, there’s a pretty significant catch right now: Dyno Autoscaling isn't available on Fir yet. For any Rails app that relies on Cedar's autoscaling to handle traffic spikes or queue lengths, that's a major hurdle for migration. You'd have to go back to manual scaling or wait until Heroku adds it to Fir. Keep an eye out on the Heroku Roadmap.
Another point, telemetry and observability looks like it's getting a really solid upgrade. Fir has native support for OpenTelemetry (OTel). Therefore, getting traces, metrics, and logs combined together should be a lot easier, with additional configuration. Imagine tracing a slow web request all the way through Rails, ActiveRecord, and maybe into a background job – that kind of thing should be simpler without needing to stitch together data from multiple add-ons. It's a modern approach, though teams will need to get comfortable with OTel concepts if they aren't already.
We have noted however that some of the key features available in Cedar Private Spaces aren't in Fir just yet. Things like Internal Routing (for services talking directly to each other), Trusted IP Ranges (locking down access), and VPN connections are currently marked as 'To Be Added' or are being re-architected. If your application's security or architecture relies heavily on these Cedar features, migrating to Fir right now might be blocked or require significant workarounds. That's probably the biggest blocker for existing complex setups.
Here’s my verdict. Fir is definietly a modernisation of Heroku, embracing containers and standard observability practices. If you are building a new Rails projects, starting on Fir seems like a good idea, so you can get the benefits immediately. For your existing applications on Cedar, it's a bit trickier. The increased dyno choice and built-in telemetry are quite exciting, except the missing autoscaling and Private Space networking features could be serious considerations. Migrating your existing apps might involve careful planning, testing, and potentially waiting for Heroku to reach feature parity before even considering it. We will definitely be keeping an eye on Heroku’s future roadmap, Fir looks extremely promising, and once feature parity is achieved, I’d say it’s a no-brainer.
Need help migrating to Fir? Contact reinteractive
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