Re: libipvs

["Alexandre CASSEN" <alexandre.cassen@xxxxxxxxxxxxxx>]

Hi Jeremy,

> Is there any documentation available for the libipvs interface? I'm
wanting
> to add/remove realservers from the ipvs table and change the server
weights.
>
> If not, I'll just look at how it's done in ipvsadm.

Here is a quick example on howto use libipvs (the code is taken from
Keepalived: ipvswrapper.c):

[Pseudo code is used]

1. For conventional use define a ipvs_talk function as follow :

=> This function is responsible of sending request to IPVS kernel code
using libipvs interface.
=> cmd is the command type and can take the following value (ipvs syncd
excluded from the list) :
      o IP_VS_SO_SET_ADD
      o IP_VS_SO_SET_DEL
      o IP_VS_SO_SET_ADDDEST
      o IP_VS_SO_SET_DELDEST
=> I consider you are using IPVS for Kernel 2.4 series.

static int
ipvs_talk(int cmd, struct ip_vs_rule_user *urule)
{
        int result;

        /* Init IPVS kernel channel */
        if (ipvs_init()) {
                /* try to insmod the ip_vs module if ipvs_init failed */
                if (modprobe_ipvs() || ipvs_init()) {
                        printf("IPVS : Can't initialize ipvs: %s\n",
                               ipvs_strerror(errno));
                        return IPVS_ERROR;
                }
        }

        result = ipvs_command(cmd, urule);
        if (result)
                printf("IPVS : %s\n", ipvs_strerror(errno));
        ipvs_close();
        return IPVS_SUCCESS;
}


2. Define a IPVS rule creation function :

=> This function define IPVS urule that will be passed to ipvs_talk() func
=> cmd take the same values as ipvs_talk() cmd arg
=> Kernel 2.4 IPVS code is supposed used


int
ipvs_cmd(int cmd)
{
        struct ip_vs_rule_user urule;

        memset(&urule, 0, sizeof (struct ip_vs_rule_user));

        strncpy(urule.sched_name, sched, IP_VS_SCHEDNAME_MAXLEN);
        urule.weight = 1;
        urule.conn_flags = loadbalancing_kind;
        urule.netmask = ((u_int32_t) 0xffffffff);
        urule.protocol = service_type;

        if (!parse_timeout(timeout_persistence, &urule.timeout))
                printf("IPVS: illegal timeout.\n");
        if (urule.timeout != 0 || granularity_persistence)
                urule.vs_flags = IP_VS_SVC_F_PERSISTENT;

        /* VS specific */
        if (fwmark) {
                urule.vfwmark = fwmark;
        } else {
                urule.vaddr = vs_addr;
                urule.vport = vs_port;
        }

        if (cmd == IP_VS_SO_SET_ADD || cmd == IP_VS_SO_SET_DEL)
                if (granularity_persistence)
                        urule.netmask = granularity_persistence;

        /* SVR specific */
        if (cmd == IP_VS_SO_SET_ADDDEST || cmd == IP_VS_SO_SET_DELDEST) {
                urule.weight = weight;
                urule.daddr = rs_addr;
                urule.dport = rs_port;
        }

        /* Talk to the IPVS channel */
        return ipvs_talk(cmd, &urule);
}

The values used here are :

o sched : Load balancing scheduler
      - Type : char *
      - Values : rr, wrr, lc, wlc, lblc, dh, sh

o loadbalancing_kind : Routing method
      - Type : char *
      - Values : NAT, DR, TUN

o service_type : Virtual service type
      - Type : uint16_t
      - Value : IPPROTO_TCP, IPPROTO_UDP

o timeout_persistence : Timeout for persistent virtual services definition
      - Type : char[5]
      - Value : integer string

o granularity_persistence : Persistence Granularity
      - Type : uint32_t
      - Value : inet_addr() 32 bit network representation

o fwmark : Virtual Service is a firewall mark
      - Type : int
      - Value : integer

o vs_addr & vs_port : Virtual service definition
      - Type : vs_addr = uint32_t , vs_port = uint16_t
      - Value : vs_addr is a network representation 32bit of IP address of
the virtual service

o rs_addr & rs_port : Real service definition (the same as vs_addr &
vs_port definition)

o weight : Real service weight definition
      - Type : int
      - Value : integer


=> modprobe_ipvs(...) & parse_timeout(...) funcs are coming from ipvsadm.c
code.


The description bellow is very short, for more information on other
option/definition (ipvs syncd manipulation) please look into ipvsadm code.

Best regards,
Alexandre