DNS-Based Service Discovery
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dns-pod-service
How does DNS work in K8S
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Tuning ndots
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refer2

NodeLocal DNSCache
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debug

Debug

container1: ping google.com
same network namespace: sudo nsenter -t xxx -n tcpdump -i eth0 udp port 53

UDP tuning for coredns

        'net.core.netdev_budget = 900',
        'net.core.netdev_max_backlog = 131072',
        'net.core.rmem_default = 262144000',
        'net.core.rmem_max = 262144000',