Cases2 cases

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1. IL-0356 Every domain hosted on Railway returned HTTP 404 to new connections for five minutes because route lookups failed

   Railway2026

   Symptoms

   On 30 September 2026, between about 07:35 and 07:40 UTC, new connections to every domain hosted on Railway, both custom domains and *.up.railway.app domains, got HTTP 404 in all regions. Internal alerting paged the on-call team as soon as route lookups started to fail.

   Service outageDNS resolution failures

   Trigger

   At 07:29 UTC an engineer merged a change to the routing control plane that contained a database schema update and a new version of the routing service. At about 07:35 the deployment system rolled the new routing service out to every region before the schema update had been applied.

   Root cause

   Faulty deployment

   Component

   Network control plane (SDN)DatabaseCI system

   Contributing factor

   Unsafe failure behaviourNo staged rolloutExcessive blast radius

   Detection

   Internal alerting engaged the on-call response team as soon as route lookups began to fail at about 07:35 UTC.

   Remediation

   • Let the CI system finish the schema update, after which the routing service's retried lookups succeeded and routing recovered without a rollback

   Action items

   • Force the migration rollout to run in serial order and unify the deployment pipeline so deploy order and blast radius are checked before merge
   • Block the routing service's blue/green rollout until the database schema matching its version is in place
   • Add shard based rollouts per region to the distributed control plane to isolate impact

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2. IL-0350 Hosts in an IONOS TXL cluster lost connectivity when an InfiniBand fabric resweep failed on a full multicast table

   IONOS Cloud2026

   Symptoms

   On 3 March 2026, during a scheduled maintenance to replace a faulty switch in a cluster in IONOS Cloud's TXL data center, monitoring alerts fired and the hosts in that cluster lost network connectivity. Customers saw intermittent network degradation or outages, and the Data Center Designer (DCD) web frontend and the AI Model Hub became unreachable.

   Network unreachableLink flappingService outage

   Trigger

   During a scheduled maintenance to replace a faulty switch, Topology 2 of 2 in the affected cluster was disabled as planned, and a link flap on a switch in Topology 1 then flooded the InfiniBand control plane with alerts and started a fabric resweep.

   Root cause

   Capacity exhaustion

   Component

   InfiniBand fabricNetwork control plane (SDN)BGP routingNIC, cable and switch port linkModel hubDatabase

   Contributing factor

   Automation amplificationExcessive blast radius

   Detection

   IONOS began investigating monitoring alerts in TXL; the first status update was posted at 11:36 UTC.

   Remediation

   • Switched from the affected control plane to its standby
   • Rebooted the locked-up gateways
   • Recovered Topology 1 from the scheduled maintenance
   • Paused provisioning in the cluster that had a backlog of queued jobs
   • Re-enabled provisioning once network connectivity improved and watched job execution
   • Re-established connectivity for the systems that support the DCD

   Action items

   • Adjusted the control-plane configuration to use less aggressive failover timers and reduced heavy sweep activity, lowering the load on the forwarding table
   • Reduced the number of multicast group memberships to relieve the forwarding table
   • Set up continuous monitoring of forwarding table use and control-plane memory with alerts before capacity limits are reached
   • Move the control plane to dedicated high-performance servers, separate from data-plane traffic
   • Audit IPv6 configurations and IPoIB driver settings
   • Modernise the interconnect fabric, including switches, gateways and drivers
   • Hardened IAM maintenance protocols so that critical identity services keep working when the primary Cloud APIs are temporarily unavailable
   • Move IAM to a dedicated platform without a dependency on the standard managed Kubernetes clusters
   • Introduce a dedicated provisioning provider for DBaaS and Managed Kubernetes
   • Add automated circuit breakers to the provisioning engine against overload and queue buildup from self-healing services
   • Improve visibility and control over job execution and prioritisation in the provisioning queue
   • Change the provisioning queue architecture to decouple services and reduce spillover

   Lessons

   IONOS identified the linking of services through the shared provisioning queue as a key reason the degradation lasted as long as it did. Alongside making each service more robust, it is decoupling the provisioning queue and addressing dependencies between services to reduce the blast radius of future incidents.

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