Cases2 cases

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1. IL-0098 After 2i2c moved from ingress-nginx to nginx-ingress, a hub's Ingress took priority over cert-manager's temporary Ingress for the same host, so new hubs could not get TLS certificates

   2i2c2026

   Symptoms

   An attempt to launch a new hub failed because its ingress could not obtain a new TLS certificate. The day before, the same engineer had recreated the support deployment on the 2i2c-aws-us cluster and seen its TLS certificate orders stuck pending.

   Misrouted requestsDeploys failing

   Trigger

   Creating new hub deployments that needed new TLS certificates on clusters recently migrated from ingress-nginx to nginx-ingress.

   Root cause

   Breaking change in an upgrade

   Component

   Ingress controllercert-manager

   Contributing factor

   Change with a delayed effect

   Detection

   An attempt to launch a new hub failed; the engineer had seen certificate orders stuck pending on another cluster the day before and declared an incident.

   Remediation

   • annotated the Ingress objects that need TLS so that cert-manager could edit them in place to complete the ACME challenge

   Action items

   • Follow-up tracked in https://github.com/2i2c-org/infrastructure/issues/8016
   • Follow-up tracked in https://github.com/2i2c-org/infrastructure/issues/3278

   Lessons

   Swapping one ingress controller for another can change how Ingress objects that share a host are combined. cert-manager's temporary challenge Ingress depends on that behaviour, so the breakage shows up when a deployment needs a new certificate. 2i2c notes that it got lucky: it had already learned of this possible cause while testing on an internal cluster, and changing the cert-manager configuration was quick.

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2. IL-0173 cert-manager's preferredChain logic picked the Let's Encrypt chain through the expired DST Root CA X3, so clients built on an old BoringSSL could not connect to a development server

   Devsisters2024

   Symptoms

   On 13 February 2024, when Devsisters' infrastructure cell came back from the Lunar New Year holiday, it received a request to look into a development server that could not be reached. No one had made a manual change over the holiday.

   TLS certificate errors

   Trigger

   On 8 February 2024, in the first phase of retiring the DST Root CA X3 cross-sign, Let's Encrypt made the ISRG Root X1 chain its default chain and began offering the DST Root CA X3 chain as the alternate.

   Root cause

   Software defect

   Component

   cert-manager

   Contributing factor

   –

   Detection

   On 13 February, after the Lunar New Year holiday, a request came in to the infrastructure cell that the development server could not be reached; while inspecting the certificate chain the server presented, the team found it serving the chain through the expired DST Root CA X3.

   Remediation

   • submitted a pull request fixing cert-manager's preferred chain selection, which was merged

   Lessons

   A latent bug can stay hidden until an upstream provider changes a default. cert-manager's preferredChain matching gave the intended result while DST Root CA X3 was Let's Encrypt's default chain and the wrong one after the default changed. An expired root at the top of a served chain is harmless to most TLS clients, which fall back to the trusted ISRG Root X1 below it, but fatal to an implementation such as an old BoringSSL that checks the trust anchor's validity and insists on verifying the topmost certificate. ACME clients choose the preferred chain with different heuristics, so the same preferredChain value can behave differently between Certbot and cert-manager.

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