Incidents/2023-01-17 asw-b2-codfw failure redux

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document status: final


Incident metadata (see Incident Scorecard)
Incident ID 2023-01-17 asw-b2-codfw failure redux Start 2023_01_17 13:00:00
Task T327001 End not ongoing/follow up stage
People paged ? Responder count ?
Coordinators effie, inflatador Affected metrics/SLOs
Impact All hosts in codfw row B lost network connectivity. End-user impact TBD.

Two main issues happened during this window:

  1. The prep work to bring online the replacement switch from the prior incident triggered a Junos bug which brought instability in row B (mostly impacting connectivity between the different switches in row B)
  2. Another Junos bug (triggered by an operator error) broke IPv6 connectivity for the whole row

The first point was quickly fixed, while the 2nd required onsite work to minimize downtime as it required B2 to come back up to be able to reboot B7 (those two are the uplinks to the core routers).

Switch status during incident
Switch status during incident


All times in UTC.

  • 12:49: #pages for hosts down in codfw
  • 12:57: codfw frontend depooled geoip/generic-map/codfw => DOWN
  • 13:00 Incident opened. effie becomes IC.
  • 13:01: conftool action : set/pooled=false; selector: dnsdisc=restbase-async,name=codfw
  • 13:01 : conftool action : set/pooled=true; selector: dnsdisc=restbase-async,name=.*
  • 13:12: Klaxxoned all SREs
  • 13:13: START - Cookbook sre.discovery.service-route check citoid: maintenance
  • 13:14: START - Cookbook sre.discovery.service-route depool mobileapps in codfw: maintenance
  • 13:14: <Emperor> depool swift from codfw [ sudo confctl --object-type discovery select 'dnsdisc=swift,name=codfw' set/pooled=false]
  • 13:16: misconfiguration on router fixed, IPv4 works, IPv6 still not working
  • 13:26 _joe_: depooling all services in codfw
  • 13:27: jynus: restarting manually replication on es2020, may require data check afterwards
  • 13:35: mvernon: conftool action : set/pooled=false; selector: dnsdisc=thanos-swift,name=codfw
  • 13:35: mvernon: conftool action : set/pooled=false; selector: dnsdisc=thanos-query,name=codfw
  • 13:37: jiji: conftool action : set/pooled=false; selector: dnsdisc=recommendation-api,name=codfw
  • 13:40: claime: investigating unreachable etcds on ganeti host ganeti2020.codfw.wmnet
  • 14:10: restart cassandra on aqs2005 (didn’t help)
  • 14:39: topranks: I added a static ARP entry for the secondary IPv4 addresses belonging to restbase2013 on cr2-codfw and they are reachable again
  • 14:39: so the issue is similar to the IPv6 problem, in that the switch is not forwarding certain multicast/broadcasts (some ARP, all ICMPv6 ND)
  • 15:26: XioNoX: we're going to bring B2 into the row B virtual chassis,
  • 15:29: :XioNoX: rack B2 comming up, looks stable
  • 15:42: claime: etcd clusters OK
  • 16:20 inflatador becomes IC
  • 16:59 effie: !log pooling back depooled mw servers in codfw
  • 17:07 bblack: confirmed that all B2 hosts seem to be on private1-b-codfw, and yeah all have the :118: issue (except the one I manually fixed)
  • 17:16 bblack: │ trying the cumin run
  • 17:17: bblack: [done]


  • 12:49: LibreNMS alerts fired. Example verbiage: Alert for device asw-b-codfw.mgmt.codfw.wmnet - virtual-chassis crash
  • The issues were triggered by Netops work, so engineers were already looking and identified the bugs quickly

Did the appropriate alert(s) fire? Was the alert volume manageable? Did they point to the problem with as much accuracy as possible?

Yes and yes


What went well?

  • Alerts helped pinpoint the root cause almost immediately
  • The prep work was done in advance of scheduled onsite work
  • Most services continued to work over IPv4 when IPv6 was not working

What went poorly?

  • The eqiad and codfw Juniper virtual chassis are particularly sensitive to switch replacements
  • Some of codfw switches are cabled differently from our standards, resulting in some virtual-chassis cables being already connected on the "to be configured" switch
  • We hit two different bugs in the same window

Where did we get lucky?

  • Incident happened during EU working hours
  • Services were already depooled from Saturday's incident (some luck, but also good judgement from Saturday's responders)

Links to relevant documentation



Incident Engagement ScoreCard
Question Answer


People Were the people responding to this incident sufficiently different than the previous five incidents? no
Were the people who responded prepared enough to respond effectively yes
Were fewer than five people paged? no
Were pages routed to the correct sub-team(s)? yes
Were pages routed to online (business hours) engineers?  Answer “no” if engineers were paged after business hours. yes
Process Was the "Incident status" section atop the Google Doc kept up-to-date during the incident? yes
Was a public entry created? no
Is there a phabricator task for the incident? yes T327001
Are the documented action items assigned? no No action items yet, will consult with more experienced SREs before creating
Is this incident sufficiently different from earlier incidents so as not to be a repeat occurrence? yes
Tooling To the best of your knowledge was the open task queue free of any tasks that would have prevented this incident? Answer “no” if there are

open tasks that would prevent this incident or make mitigation easier if implemented.

Were the people responding able to communicate effectively during the incident with the existing tooling? yes
Did existing monitoring notify the initial responders? yes
Were the engineering tools that were to be used during the incident, available and in service? yes
Were the steps taken to mitigate guided by an existing runbook? no Originally a question mark, so defaulting to no
Total score (count of all “yes” answers above) 10