server-selection

This attribute determines how Radiator selects an LDAP server when multiple server blocks are configured. Possible values are:

• fallback: Servers are tried in priority order. The highest-priority available server receives every request. Lower-priority servers are used only when higher-priority servers are unavailable or degraded.
• round-robin: Requests are distributed across all available servers in rotation. If a server fails, the next available server in the rotation is used.
• no-fallback: Only the highest-priority available server is tried for each request. If the operation fails on that server, the request fails without retrying on other servers.
• least-connections: Each request is routed to the available server with the fewest in-use connections. If that server also fails, the next least-loaded server is tried. When servers are tied, servers with a lower priority value are preferred; within the same priority, alphabetical name order is used as a tiebreaker — the same as fallback. Because saturated pools are skipped immediately for LDAP, this strategy is useful for balancing load under high concurrency.

Default: fallback

Example configuration:

ldap "LDAP_HA" {
    server-selection least-connections;

    server "LDAP1" {
        url "ldap://ldap1.example.com:389/";
        timeout 3s;
        shared-connections 10;
        exclusive-connections 10;
        authentication {
            dn "cn=radiator,dc=example,dc=com";
            password "secret";
        }
    }

    server "LDAP2" {
        url "ldap://ldap2.example.com:389/";
        timeout 3s;
        shared-connections 10;
        exclusive-connections 10;
        authentication {
            dn "cn=radiator,dc=example,dc=com";
            password "secret";
        }
    }

    search "FIND_USER" {
        base "dc=example,dc=com";
        scope sub;
        filter "(&(uid=%{aaa.identity})(objectClass=inetOrgPerson))";
        mapping {
            user.username = uid;
            vars.dn = entry::dn;
        }
    }
}

See Backend Load Balancing for more details and examples.