• Elastic Load Balancing

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  5. What Are the Precautions of Using UDP?

What Are the Precautions of Using UDP?

  • Health check uses UDP and ping packets to detect the status of backend servers. To ensure smooth transmission of these packets, ensure that ICMP is enabled on the backend servers by performing the following:

    Log in to the backend servers and run the following command as user root:

    cat /proc/sys/net/ipv4/icmp_echo_ignore_all

    • If the returned value is 1, ICMP is disabled.
    • If the returned value is 0, ICMP is enabled.
  • If UDP is used, the health check result may be different from the actual status of servers.

    If a backend server runs Linux, the rate of ICMP packets on the server is limited due to the anti-ICMP attack protection mechanism of Linux. In this case, when a service exception occurs, ELB will not receive error message port XX unreachable and still determine that the health check is successful. This results in an inconsistency between the health check result and the actual server status.

  • A listener that uses the UDP protocol cannot be not added to a private network classic load balancer.