ZeroMQ

Model One: Simple Retry and Failover

So, our menu appears to offer the following choices: simple, brutal, complex, or nasty. Let’s start with simple and then work out the kinks. We’ll take Lazy Pirate and rewrite it to work with multiple server endpoints. We’ll start one or several servers first, specifying a bind endpoint as the argument (Example 4-77).

Example 4-77. Freelance server, Model One (flserver1.c)

//
//  Freelance server - Model One
//  Trivial echo service
//
#include "czmq.h"

int main (int argc, char *argv [])
{
    if (argc < 2) {
        printf ("I: syntax: %s <endpoint>\n", argv [0]);
        exit (EXIT_SUCCESS);
    }
    zctx_t *ctx = zctx_new ();
    void *server = zsocket_new (ctx, ZMQ_REP);
    zsocket_bind (server, argv [1]);

    printf ("I: echo service is ready at %s\n", argv [1]);
    while (true) {
        zmsg_t *msg = zmsg_recv (server);
        if (!msg)
            break;          //  Interrupted
        zmsg_send (&msg, server);
    }
    if (zctx_interrupted)
        printf ("W: interrupted\n");

    zctx_destroy (&ctx);
    return 0;
}

Then we’ll start the client (Example 4-78), specifying one or more connect endpoints as arguments.

Example 4-78. Freelance client, Model One (flclient1.c)

//
//  Freelance client - Model One
//  Uses REQ socket to query one or more services
//
#include "czmq.h"

#define REQUEST_TIMEOUT     1000
#define MAX_RETRIES         3       //  Before we abandon

static zmsg_t *
s_try_request (zctx_t *ctx, char *endpoint, zmsg_t *request)
{
    printf ("I: trying echo service at %s...\n", endpoint);
    void *client = zsocket_new (ctx, ZMQ_REQ);
    zsocket_connect ...