---
title: "More Predictable Shared Dyno Performance"
description: "Heroku describes a year-long effort to make CPU access more predictable for shared dynos in the Common Runtime. Previously, individual dynos could burst CPU use relatively freely when capacity was available, improving utilization but sometimes allowing misconfigured or malicious “noisy neighbors” to cause response-time spikes or H12 timeouts. The platform introduced improved resource isolation for eco, basic, standard-1X, and standard-2X Dynos, limiting bursts while preserving the ability to burst and aiming for fairer access to shared CPU resources. The change does not alter the number of dynos per instance, and Performance, Private, and Shield type Dynos are excluded because they run on dedicated instances."
---

# More Predictable Shared Dyno Performance

[Heroku](https://yomu.fyi/company/heroku) · Michael Friis · Apr 11, 2023

**Type:** Announcement

## Summary

Heroku describes a year-long effort to make CPU access more predictable for shared dynos in the Common Runtime. Previously, individual dynos could burst CPU use relatively freely when capacity was available, improving utilization but sometimes allowing misconfigured or malicious “noisy neighbors” to cause response-time spikes or H12 timeouts. The platform introduced improved resource isolation for eco, basic, standard-1X, and standard-2X Dynos, limiting bursts while preserving the ability to burst and aiming for fairer access to shared CPU resources. The change does not alter the number of dynos per instance, and Performance, Private, and Shield type Dynos are excluded because they run on dedicated instances.

## Context

Shared dynos previously had relatively liberal CPU bursting. Although this improved overall resource utilization, customers sometimes experienced degraded performance from noisy neighbors, including random response-time spikes and H12 timeouts.

## Approach / What changed

Heroku rolled out improved resource isolation for shared dyno types over the course of a year. The change limits CPU bursting for eco, basic, standard-1X, and standard-2X Dynos while retaining some burst capacity; it does not change the number of dynos running on each instance.

## Takeaways

- Shared dynos can still burst CPU use, but less extensively than before, prioritizing fairer and more predictable access to shared resources.
- Noisy neighbors could cause random request-response spikes or H12 timeouts when other dynos consumed much more than their fair share.
- Performance, Private, and Shield type Dynos are unaffected because they run on dedicated instances.

**Tags:** [Cloud Native Buildpacks](https://yomu.fyi/topic/cloud-native-buildpacks), [Reliability](https://yomu.fyi/topic/reliability)

- Source: [Heroku](https://www.heroku.com/blog/more-predictable-shared-dyno-performance)
- Source URL: https://www.heroku.com/blog/more-predictable-shared-dyno-performance
- Ingested by Yomu: 2026-09-09T20:03:42.686Z

[Read original post](https://www.heroku.com/blog/more-predictable-shared-dyno-performance)