Heroku Generations

Last updated April 14, 2025

A generation refers to a specific version or iteration of the Heroku platform’s underlying infrastructure and tools used to run applications. Each generation represents a significant upgrade or evolution in Heroku’s technology stack, offering improved performance, security, and features.

Both the Common Runtime and Private Spaces run on the Cedar generation of the platform. Starting in 2025, Heroku is upgrading to the next generation of the platform: Fir.

Fir is now generally available with Fir Private Spaces.

Cedar

The Legacy Platform

Heroku’s Cedar generation was a significant leap forward in platform capabilities. It introduced a streamlined HTTP stack, enabling advanced HTTP features and paving the way for a more flexible and powerful platform.

Key Features of Cedar

  • Polyglot support: Beyond the official set of Heroku languages, Cedar has a rich library of custom classic buildpacks contributed by partners or community developers.

  • Heroku run: The ability to execute arbitrary one-off dynos, providing flexibility for various tasks.

  • Procfile and process model: A robust mechanism for managing diverse application processes. Cedar was a cornerstone of Heroku’s platform for many years, offering a reliable, performant, and feature-rich environment for developers.

Fir

The Future of Heroku

Heroku’s latest generation, Fir, builds upon the strengths of Cedar while introducing a new era of developer experience, performance, and flexibility. Fir leverages modern cloud-native technologies to provide a seamless and efficient platform.

Key Features of Fir

  • Streamlined deployments: Deploy your applications effortlessly with a single command, utilizing Cloud Native Buildpacks to automate the containerization process.

  • Simplified and diversified dyno options: Scale your applications with ease using intuitive controls and intelligent defaults, powered by Kubernetes.

  • Integrated observability: Gain deep insights into your application’s performance with OpenTelemetry, seamlessly integrated into Fir and Heroku Metrics. Fir offers a powerful and predictable platform that empowers developers to build modern, cloud-native applications while maintaining the familiar Heroku developer experience.

Here are some of the key benefits of using Fir compared to the Cedar version of Private Spaces:

  • Cloud native, open-source standards: Future-proof your apps with scalable solutions built on Kubernetes, OCI containers, and OpenTelemetry. Easily integrate with modern cloud ecosystems.
  • Operational excellence: Powered by AWS services like EKS, Graviton, and Global Accelerator, delivering scale, resilience, and performance to keep your business running smoothly.
  • Access to new features: The most modern product and feature development is happening on Fir. Start building on the new generation now to have first access to new features and platform improvements.

Fir New Feature Development Roadmap

The following new features are available or are coming to Fir. These features are not available in the Cedar generation.

Available Coming
Kubernetes-based GPU dynos
Graviton / ARM64 dynos OpenTelemetry log egress add-on support
IPv6 support OpenTelemetry log ingress add-on support
Cloud Native Buildpack builds HTTP/2 to the dyno
In-space builds HTTP/3 support
More than 500 dynos per space Software Bill-of-Materials
Native OpenTelemetry (traces, metrics, logs) Dyno health check support
OpenTelemetry drains Enhanced Heroku networking firewalls
Base image updates with CNB rebase Blue/green deployments

Feature Parity

We’ll update this table as we add features to Fir. You can also subscribe to our changelog to stay informed.

Feature Fir Cedar
Heroku run:inside X X
One-off dynos (heroku run:detached) X X
Private databases X X
Logs X (Third-party add-on logs not yet available) X
Log drains X X
Encrypted Config Vars X X
Github integration (auth, sync, chatops) X X
git push (Git service) X X
Custom Buildpacks X X
Automated Certificate Management (Heroku ACM) X X
Heroku Routing X X
Usage tracking and dashboard display X X
Add-on support X X
Pipelines (incl. promotions) X X
Review Apps X X
Release Phase X X
HTTP/2 to the Router X X
Heroku App Metrics X (Router health and some events/errors coming.) X
Threshold Alerts X X
Heroku ACM wildcard domains X X
Dyno autoscaling To Be Added X
Common Runtime To Be Added X
ISO and SOC compliance To Be Added X
Shield compliance To Be Added X
Heroku run (CLI Command and Dashboard Console) To Be Added X
Heroku CI To Be Added X
Network error logging To Be Added X
Trusted IP ranges To Be Added X
Internal routing To Be Added X
VPC peering To Be Added X
VPN support To Be Added X
Private Spaces DNS Service Discovery. To Be Added X
x86 architecture support To Be Added X
Router maintenance & error pages To Be Added X
Clojure support To Be Added X
Montreal Private Space Region Support To Be Added X

Cedar-Only Features

Some features from Cedar-generation Private Spaces have been or will be replaced by improved Fir-only features.

Key Differences in the Fir Platform Generation

As we enhance Heroku with the new Fir platform generation, we’re introducing powerful capabilities. While we work towards feature parity with our previous Cedar generation, there are some important distinctions to understand when migrating or starting new projects on Fir.

Dyno Architecture: Graviton/ARM Only (Currently)

The Fir platform currently exclusively uses Graviton (ARM) processors for its dynos.

What this means for you: Applications or dependencies compiled specifically for x86 architecture likely fail to build or run on Fir.

Recommendation: Ensure your application and its dependencies are compatible with ARM architecture.

Future Plans: Support for x86-based dynos is on our Fir roadmap.

Networking: Default IPv6 for Private Spaces

Fir utilizes IPv6 as the default and recommended connection protocol for networking within Heroku Private Spaces.

What this means for you: If you designed your application, its dependencies, or connected services within a space assuming only IPv4 connectivity, they don’t bind properly on Fir.

Recommendation: Ensure IPv6 compatibility by correctly binding to an IPv6 listener or the dual-stack address listener in your app’s language (typically ::) to leverage Fir’s networking configuration.

Builds: Cloud Native Buildpacks (CNB) Required

The Fir platform exclusively uses Cloud Native Buildpacks (CNB) for building applications. The previous classic Heroku buildpacks used on the Cedar stack unsupported on Fir. In addition, building Docker images with heroku.yml and the container stack are unsupported in Fir.

What this means for you: If your application relies on a classic buildpack, including custom forks, the app may fail to build on Fir. If your application relies on the container stack, you can’t migrate it to Fir.

Recommendation: Migrate your build process to use compatible CNBs. Consult the Cloud Native Buildpacks article to understand how to adapt your application.

Build Strategy: Monorepo Builds Not Yet Supported

The current implementation of Cloud Native Buildpacks on the Fir platform has no support for building applications directly from a monorepo structure (a single repository containing multiple deployable applications or services).

What this means for you: Standard monorepo tooling integrations may not function as expected during the build phase on Heroku.

Recommendation: Ensure each application intended for deployment on Fir resides in its own dedicated repository or be structured such that the CNB build process targets only a single application within the repository root or via configuration.

Future Plans: Support for streamlined monorepo builds is under roadmap consideration.

Logs: OpenTelemetry Instead of Syslog Drains

Fir supports OpenTelemetry (OTel) metrics, logs, and traces via telemetry drains. Syslog drains are not available today.

What this means for you: Third-party OTel-native observability platforms work out of the box. Request tracing functionality is enabled without additional instrumentation. Tooling that relies on syslog format is not yet be compatible with Fir.

Recommendation: Use OTel-native observability tooling to monitor signals of interest. Heroku app metrics and alerting are also available. Open-source SDKs are available for additional language-specific signals.

Future Plans: We have additional OTel signal enhancements planned. We are evaluating support for syslog drains on Fir and working with the Heroku Elements partners that rely on them to ensure continuity of experience.

Fir Compliance

The compliance certifications that exist under the Cedar generation will be coming to Fir with the introduction of certifications for SOC 1, 2, 3. We can’t consider Fir certified for any particular compliance program until we receive the proper reports from our external auditors. We will announce the certifications for the various compliance programs in changelogs and update the appropriate documentation in the Heroku Dev Center.

Upgrade to Fir

While Cedar remains a reliable choice, Heroku recommends migrating to Fir for new applications and actively developed projects. Fir offers a more modern, efficient, and feature-rich platform.

By embracing Fir, you can take advantage of the latest advancements in cloud-native technology and accelerate your development workflow.

Get Started with Fir

Start exploring by trying out one of our Getting Started guides:

Have Feedback?

To report any findings or bugs during the pilot program, open a ticket at https://help.heroku.com/. The ticket will get escalated to our product team for review. You’re also encouraged to leave feedback in our Public Roadmap Item to generate a public conversation where our product team can also assist.

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