Improved Kubernetes API server load balancing and strict RFC compliance
Section titled “Improved Kubernetes API server load balancing and strict RFC compliance”We are updating our ingress mechanism to make use of improved Kubernetes API server load balancing in the STACKIT Kubernetes Engine (SKE). We will begin rolling out this update gradually across all clusters starting September 15, 2026. This update significantly benefits the overall stability of SKE and decreases the response times from the API servers under high load.
To achieve this improved load balancing, the new ingress mechanism strictly enforces RFC compliance. This means that misconfigured clients—specifically those where the Server Name Indication (SNI) does not match the Host or :authority HTTP header—will be rejected with a 421 Misdirected Request error. Previously, these clients might have worked because the former L4 load balancers did not take HTTP headers into consideration.
As we roll out this change gradually across our production environments, non-compliant clients will receive a 421 Misdirected Request error when attempting to access the API server. To ensure a smooth transition and minimize disruption, we are proactively monitoring our logs for these 421 Misdirected Request errors. If we detect that your cluster is affected during the rollout, our support team will:
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Temporarily apply a compatibility fix on our end to restore your traffic flow.
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Open a support ticket to notify you, providing your project ID and cluster details.
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Inform you of the temporary nature of this fix and provide a strict deadline to update your non-compliant clients before the compatibility mode is permanently removed.
To learn how to make sure your clients stay compatible, refer to our how-to guide “Ensure RFC-compliant API requests to your SKE cluster”.