Calls to core DNS are timing out

Question

Calls to core DNS are timing out

Jan Jannink 0

We are seeing timeouts of this type in the logs of our kubernetes cluster as we contact core DNS:


requests.exceptions.ConnectionError: HTTPSConnectionPool(host='openaipublic.blob.core.windows.net', port=443): Max retries exceeded with url: /encodings/cl100k_base.tiktoken (Caused by NameResolutionError("

Anusree Nashetty 4,790 Reputation points Microsoft External Staff Moderator

2025-06-26T22:35:19.2066667+00:00

Hi Jan Jannink,

Could you please tell us if the issue is intermittent.
Which type of DNS are you using, is it Custom DNS or Azure provided DNS.
Please run the nslookup on source machine and provide the result here.

Also, could you please elaborate the issue, any document if you are using.
Anusree Nashetty 4,790 Reputation points Microsoft External Staff Moderator

2025-06-27T23:26:23.0166667+00:00

Hi Jan Jannink,

Please provide above details, we can assist you in detail. Thank you.
Anusree Nashetty 4,790 Reputation points Microsoft External Staff Moderator

2025-07-01T17:10:19.8266667+00:00

Hi Jan Jannink,

Did you get a chance to see my response. If you have any further queries, let me know. If the information is helpful, please click on Upvote.

1 answer

Your answer

Anusree Nashetty 4,790 Reputation points Microsoft External Staff Moderator

2025-06-26T22:35:19.2066667+00:00

Hi Jan Jannink,

Could you please tell us if the issue is intermittent.
Which type of DNS are you using, is it Custom DNS or Azure provided DNS.
Please run the nslookup on source machine and provide the result here.

Also, could you please elaborate the issue, any document if you are using.
Anusree Nashetty 4,790 Reputation points Microsoft External Staff Moderator

2025-06-27T23:26:23.0166667+00:00

Hi Jan Jannink,

Please provide above details, we can assist you in detail. Thank you.
Anusree Nashetty 4,790 Reputation points Microsoft External Staff Moderator

2025-07-01T17:10:19.8266667+00:00

Hi Jan Jannink,

Did you get a chance to see my response. If you have any further queries, let me know. If the information is helpful, please click on Upvote.

Answer 1

Hi Jan Jannink,

As per my understanding, I have provided the troubleshooting steps:

Check if CoreDNS pods are restarting or under pressure. If you're using coredns, it may be misconfigured or not scaling.

Enable NodeLocal DNS Cache, this significantly reduces DNS lookup latency and load on CoreDNS. https://kubernetes.io/docs/tasks/administer-cluster/nodelocaldns/

If using Azure-provided DNS: Ensure egress to Azure DNS IP 168.63.129.16 is not blocked. Confirm CoreDNS is forwarding to this IP.

If using custom DNS: Verify the upstream DNS server is reachable from the node subnet. Ensure the custom DNS is responsive and not intermittently timing out.

If you have any further queries, let me know. If the information is helpful, please click on Upvote.

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Calls to core DNS are timing out

1 answer

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