round robin backends in varnish

init.vcl

import directors;

backend ay_p_www1 {
    .host = "10.10.0.137";
    .port = "80";
    .probe = {
        .url = "/status";
        .timeout = 1s;
        .interval = 5s;
        .window = 5;
        .threshold = 3;
    }
}

backend ay_p_www2 {
    .host = "10.10.0.138";
    .port = "80";
    .probe = {
        .url = "/status";
        .timeout = 1s;
        .interval = 5s;
        .window = 5;
        .threshold = 3;
    }
}
# …

sub vcl_init {
    new cluster = directors.round_robin();
    cluster.add_backend(ay_p_www1);
    cluster.add_backend(ay_p_www2);
    # …
}