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  • Detect and fix rare cases where the primary ENI does not serve default traffic

    calendar Jul 27, 2025 · 3 min read · Linux EC2  ·
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    During testing, we encountered a rare scenario when launching EC2 instances with multiple ENIs: the primary ENI (device index 0) does not serve default network traffic. This occurs in approximately 1 out of 10,000 launches (0.01%). For example, when configuring two ENIs on an instance—ENI-0 (deviceIndex=0) from …


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Peng Zhang

Software Engineer

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