Cases6 cases

3 to 6 of 6

1. IL-0530 Virtual router controllers in us-central1 ran out of memory in a loop, cutting networking for new and migrated VMs

   Google Cloud2023

   Symptoms

   On 5 October 2023 in us-central1, newly created VMs waited a long time before their networking worked, and VMs that had been live migrated lost connectivity for a long time after the migration. Networking telemetry showed cross-region packet loss to and from us-central1 from 03:08 US/Pacific. Health check state of VMs reached load balancers late.

   Packet lossNetwork unreachableOOMKilledStale endpoint routingCluster or node provisioning stall

   Trigger

   A management plane behaviour change, meant to decouple the processing of API updates to Instance Groups and Network Endpoint Groups used as load balancer backends, was deployed in us-central1 after rolling out to several other regions without incident.

   Root cause

   Faulty deployment

   Component

   Network control plane (SDN)Cloud load balancer

   Contributing factor

   Excessive blast radiusNo alert on limit

   Detection

   Engineers were alerted to slowness in the virtual network control plane in us-central1 at 21:45 US/Pacific on 4 October, before the packet loss started, and to controller failures from memory exhaustion at 02:11 on 5 October. Networking telemetry showed cross-region packet loss from 03:08.

   Remediation

   • Increased the memory allocated to the virtual network router controllers
   • Rolled back the management plane change in us-central1
   • Restarted by hand the routers that were still not accepting updates

   Action items

   • Alert proactively on memory risks and unexpected memory increases
   • Refactor the deployment configuration so engineers can reallocate memory much faster
   • Re-evaluate existing practices and add safety mechanisms for API reconciliation
   • Make management plane changes more visible across teams so the changes can be correlated faster
   • Adjust the deployment footprint so a regional API change is less likely to exhaust memory across the region at once
   • Optimise memory use in the traffic routers and their controllers

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2. IL-0473 Jenkins infrastructure went fully down after a pod IP range fix deleted every AKS node pool and could not recreate them

   Jenkins project2023

   Symptoms

   On 7 July 2023 from 11:05 to 15:25 UTC many public Jenkins infrastructure services were completely down, including get.jenkins.io, plugins.jenkins.io, accounts.jenkins.io, javadoc.jenkins.io and incrementals.jenkins.io, while ci.jenkins.io, issues.jenkins.io, repo.jenkins-ci.org and www.jenkins.io were partly or completely disrupted.

   Network unreachableResources deletedCluster or node provisioning stallService outage

   Trigger

   After the upgrade to Kubernetes 1.25 changed the range of the pods' originating IP and LDAP access was blocked, a fix (Azure PR 431) deployed at 10:55 UTC to set a proper set of pod IP ranges removed all node pools of the cluster.

   Root cause

   Configuration change

   Component

   Node poolCNI pluginCloud load balancer

   Contributing factor

   Unverified assumptionNo staged rolloutNo safeguard on destructive change

   Detection

   After the upgrade, at 10:30 UTC, the team noticed that services inside the cluster, such as accounts.jenkins.io, could not reach the LDAP service.

   Remediation

   • Created the cluster again from scratch with a fixed network setup
   • Set a custom pod CIDR in a range separate from the virtual network
   • Moved the services and their DNS records to new public IPs
   • Pushed a pull request that recorded the manual rebuild, including the IP setup, in code

   Action items

   • Protect the public IPs from deletion with a Management Lock
   • Keep the public IPs in a separate resource group and point the Kubernetes-managed load balancers to it with the service.beta.kubernetes.io/azure-load-balancer-resource-group annotation
   • Improve network diagrams and documentation so possible overlaps are visible when preparing operations
   • Avoid changing the configuration of all AKS node pools at once

   Lessons

   The team said that changing one node pool at a time would have shown the problem after the first pool and avoided a full outage, and that the public IPs should change as little as possible because users behind corporate firewalls with allow-lists depend on them. The team also noted that it could rebuild, in under 4 hours, the cluster that hosts almost all public services.

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3. IL-0396 New or live-migrated GCE instances, VPN tunnels and network load balancers were unreachable on public IPs for over 2h

   Google Cloud2017

   Symptoms

   On 30 January 2017, Google Compute Engine instances, Cloud VPN tunnels and GCE network load balancers that were created or live migrated between 10:36 and 12:42 PDT could not be reached on their public IP addresses. Resources created earlier, and instances that were not live migrated, kept working.

   Network unreachableProbe failures

   Trigger

   A large set of updates was applied to a rarely used load balancing configuration on the shared layer 2 load balancers.

   Root cause

   Software defect

   Component

   Cloud load balancerNetwork control plane (SDN)

   Contributing factor

   Excessive blast radiusGap in automated tests

   Remediation

   • Restarted the jobs that program changes into the network load balancers, so the stuck changes were processed as a batch
   • Applied the fix zone by zone between 11:36 and 12:42

   Action items

   • Increase the canary timeout so updates that hit the inefficient code path only slow network changes instead of stopping them
   • Improve the inefficient code path
   • Write new tests that check behaviour on a wider range of configurations
   • Accelerate replacing global propagation of address configuration with decentralized routing
   • Add metrics and alerting that identify this kind of issue sooner

   View case
4. IL-0494 Netlify's central load balancer IP stopped responding when Rackspace null-routed it in a DDoS, and A-record sites hung

   Netlify2016

   Symptoms

   At 8am PST on Monday, August 22, 2016, Netlify got alerts that its central load balancer, the single public IP that users point A records at, had stopped responding. Rackspace had null-routed the load balancer, so all traffic to that IP hung before it reached Netlify's servers.

   Network unreachable

   Trigger

   A DDoS attack against Netlify's central load balancer in Rackspace's Chicago datacenter, after which Rackspace null-routed the load balancer's public IP.

   Root cause

   Cloud provider outage

   Component

   Cloud load balancer

   Contributing factor

   Single point of failureLimited debug access

   Detection

   Alerts at 8am PST reported that the central load balancer had stopped responding, and Rackspace then confirmed it had null-routed the load balancer.

   Remediation

   • Started a new cluster of CDN machines in Google Compute behind a Google network load balancer
   • Gave clients who had contacted support the new public IP and told them to change their A records
   • Updated the documentation and announced the new IP on Twitter, Gitter and the status page

   Action items

   • Keep the new Google-based network IP running in place of the Rackspace load balancer
   • Release Netlify's own DNS hosting, integrated with the CDN, so domains do not depend on a fixed IP
   • Fix the status page publishing process so it is updated straight away during an issue
   • Build a mailer that sends targeted mails to all paying clients during an outage

   Lessons

   Netlify judged Rackspace's load balancer too vulnerable to DDoS and Rackspace's DDoS processes not up to the standard of other cloud providers, and expected Google's anycast-based Maglev load balancer to be more resilient. In the end, the only way to protect a domain from DDoS-related outages is not to expose any fixed IP address for it, which is why sites should use the www domain with a CNAME, or Netlify DNS, rather than a single A-record IP.

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