Cases2 cases

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1. IL-0227 Most Heroku dynos in Private Spaces lost outbound connectivity after an automated OS update restarted host networking

   Heroku2025

   Symptoms

   From 06:00 UTC on 10 June 2025, Heroku services degraded badly: customers reported intermittent logins, applications failed, and Heroku's monitoring detected widespread errors with dyno networking. Heroku's own tools and the Heroku Status Page were affected as well, which delayed communication with customers and left many of them without accurate status updates. Only at 13:58 UTC did the team find a workaround to post updates to the @herokustatus account on X.

   Network unreachableService outageHigh error rate

   Trigger

   An automated operating system update ran on Heroku's production infrastructure when it should have been disabled, and it restarted the hosts' networking services.

   Root cause

   Breaking change in an upgrade

   Component

   Host routes and routing rules

   Contributing factor

   Unpinned versionCircular dependencyLimited debug access

   Detection

   Customers reported intermittent logins, and Heroku's monitoring detected widespread errors with dyno networking. Heroku's own tools and the Heroku Status Page were affected as well.

   Remediation

   • Restarted internal instances in rotation, which gave some relief
   • Had an upstream vendor invalidate the token used for the automated updates
   • Disabled the automated upgrade service
   • Recycled dynos across the whole fleet

   Action items

   • Put permanent controls in place so no system change happens outside the controlled deployment process
   • Audit all base images for similar risks
   • Make network routing survive graceful restarts of the networking service
   • Build fully independent backup communication channels
   • Overhaul incident response tooling, including tools that run queries across the whole fleet
   • Streamline break-glass procedures for rapid access to critical systems
   • Improve monitoring to detect complex issues earlier

   Lessons

   Heroku's post-mortem names three areas: production lacked immutability controls, so an automated process could change it; communication was too slow, made worse by a status page that went down with the platform; and gaps in tooling and process made recovery take longer than it should have.

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2. IL-0373 Heroku Postgres Essential-tier databases in the EU region ran out of memory and refused connections, twice in four days

   Heroku2024

   Symptoms

   From 22:31 UTC on 27 July 2024, 33 Heroku Postgres clusters in the EU (Dublin) region could not serve requests and ran into memory problems, and some Essential-tier customers could not connect to their databases. Customers trying to reach an affected database received out of memory errors.

   Memory pressureService outage

   Trigger

   A third-party vendor deployed a change to a monitoring agent that runs on Heroku's Postgres database clusters.

   Root cause

   Software defect

   Component

   DatabaseTelemetry agent

   Contributing factor

   Monitoring blind spot

   Detection

   Heroku Support paged the technology team at 07:50 UTC on 28 July based on customer support tickets. The second occurrence also reached the technology team as an escalation from Heroku Support.

   Remediation

   • Allocated more resources and restarted the Postgres clusters, which fixed the first outage temporarily
   • Provisioned the previous version of the third-party monitoring software, which did not leak memory
   • The vendor applied an interim mitigation

   Action items

   • Add enhanced metrics collection for the third-party monitoring software
   • Evaluate the vendor's fixed release of the monitoring software and roll it out if acceptable

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