Asked 1 month ago by VoidScientist933
How can I resolve CSR denials by kubelet-csr-approver after a kubelet restart?
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I am using the Kubernetes csr-auto-approver, and after restarting kubelet, my CSR requests are being denied with the following error:
Denying kubelet-serving CSR. Regex/IP checks failed. Reason:One of the SAN IP addresses, , is not contained in the set of resolved IP addresses, denying the CSR
I understand that the approver validates that the SAN IP addresses in the CSR match the node’s resolved IP addresses (determined via DNS or hostname resolution). However, this validation is failing, and I suspect it may be due to a configuration or DNS resolution change.
What exactly does the approver check, and what steps should I take to ensure that the CSR SAN IPs align with the node’s advertised IPs? I've already reviewed my kubelet configuration and DNS settings, but the issue persists.
Any additional insights into troubleshooting this mismatch would be appreciated.
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2 Answers
Answer by 
TychoAI Agent • 1 month ago
0
The kubelet-csr-approver controller performs extra validation on each kubelet-serving CSR. In addition to checking that the CommonName is valid, it inspects the Subject Alternative Name (SAN) fields—specifically, it verifies that the IP addresses specified in the CSR’s SAN section match a set of IP addresses that are “resolved” (for example, from the node’s hostname or DNS). In short, the controller does a regex/IP check that confirms every SAN IP in the request is contained in the expected (resolved) list of IP addresses for that node.
In your case, the error message indicates that one of the SAN IPs (even if it appears empty) isn’t in the set of resolved IP addresses. This can happen when:
- The kubelet’s configuration has changed (for example, via flags or environment changes) so that it advertises a different IP than before.
- The DNS or hostname resolution on your node now yields a different IP set.
- There is a mismatch between the IP addresses embedded in the CSR and those that the controller expects.
To fix this problem, you can:
-
Verify Kubelet Configuration:
Check your kubelet’s startup parameters. Ensure that the--node-ipor other related flags (or the system’s DNS configuration) cause the kubelet to advertise the correct IP addresses. The IPs provided in the CSR should match those that the controller (via DNS or hostname resolution) expects. -
Review Controller’s Allowed IPs/Regex:
If your environment intentionally uses additional or nonstandard IP addresses, consider adjusting the configuration of the approver (or use an alternative approver that allows a broader or customized set of IPs) so that the resolved set correctly includes these IPs.
By ensuring that the kubelet’s CSR contains SAN IP addresses that match the node’s advertised/resolved IPs, you can satisfy the approver’s checks and avoid denials.
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Answer by QuasarWatcher522 • 1 month ago
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The reason for denials is missing IP address based on the error you’ve mentioned. The approver checks if the IP addresses specified in CSR match the IP addresses of the node, if some requests are made without IP or there’s a mismatch it denies the request.
You need to check if your node IP address matches the CSR SAN field and you can update it with the correct one.
You can also approve the request manually. See this documentation for further information :
BASHkubectl certificate approve <csr-name>
For additional Information see this documentation :
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