Advanced Connections

The following guide contains information specific to certain types of MongoDB configurations.

For an example of connecting to a simple standalone server, see the Tutorial. To establish a connection with authentication options enabled, see the Authentication page.

Connecting to a Replica Set

Connecting to a replica set is much like connecting to a standalone MongoDB server. Simply specify the replica set name using the ?replicaSet=myreplset URI option.

#include <bson.h>
#include <mongoc.h>

int
main (int   argc,
      char *argv[])
{
    mongoc_client_t *client;

    mongoc_init ();

    /* Create our MongoDB Client */
    client = mongoc_client_new ("mongodb://host01:27017,host02:27017,host03:27017/?replicaSet=myreplset");

    /* Do some work */
    /* TODO */

    /* Clean up */
    mongoc_client_destroy (client);
    mongoc_cleanup ();

    return 0;
}

Multiple hostnames can be specified in the MongoDB connection string URI, with a comma separating hosts in the seed list.

It is recommended to use a seed list of members of the replica set to allow the driver to connect to any node.

Connecting to a Sharded Cluster

To connect to a sharded cluster, specify the mongos nodes the client should connect to. The C Driver will automatically detect that it has connected to a mongos sharding server.

If more than one hostname is specified, a seed list will be created to attempt failover between the mongos instances.

Specifying the replicaSet parameter when connecting to a mongos sharding server is invalid.

#include <bson.h>
#include <mongoc.h>

int
main (int   argc,
      char *argv[])
{
    mongoc_client_t *client;

    mongoc_init ();

    /* Create our MongoDB Client */
    client = mongoc_client_new ("mongodb://myshard01:27017/");

    /* Do something with client ... */

    /* Free the client */
    mongoc_client_destroy (client);

    mongoc_cleanup ();

    return 0;
}

Connecting to an IPv6 Address

The MongoDB C Driver will automatically resolve IPv6 addresses from host names. However, to specify an IPv6 address directly, wrap the address in [].

mongoc_uri_t *uri = mongoc_uri_new ("mongodb://[::1]:27017");

Connecting to a UNIX Domain Socket

On UNIX-like systems, the C Driver can connect directly to a MongoDB server using a UNIX domain socket. Simply pass the path to the socket, which must be suffixed with .sock.

mongoc_uri_t *uri = mongoc_uri_new ("mongodb:///tmp/mysocket.sock");

Connecting directly to a UNIX domain socket is not a common practice.

Connecting to a server over SSL

These are instructions for configuring TLS/SSL connections.

Basic Configuration

To run a server locally (on port 27017, for example):

$ mongod --port 27017 --sslMode requireSSL --sslPEMKeyFile server.pem --sslCAFile ca.pem

Add /?ssl=true to the end of a client URI.

mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?ssl=true");

Specifying Client Certificate

MongoDB requires client certificates by default, unless the --sslAllowConnectionsWithoutCertificates is provided. The C Driver can be configured to present a client certificate using a mongoc_ssl_opt_t:

const mongoc_ssl_opt_t *ssl_default = mongoc_ssl_opt_get_default ();
mongoc_ssl_opts_t ssl_opts = { 0 };

/* optionally copy in a custom trust directory or file; otherwise the default is used. */
memcpy (&ssl_opts, ssl_default, sizeof ssl_opts);
ssl_opts.pem_file = "client.pem" 

mongoc_client_set_ssl_opts (client, &ssl_opts);

The client certificate provided by pem_file must be issued by one of the server trusted Certificate Authorities listed in --sslCAFile, or issued by a CA in the native certificate store on the server when omitted.

To verify the server certificate against a specific CA, provide a PEM armored file with a CA certificate, or contatinated list of CA certificates using the ca_file option, or c_rehash directory structure of CAs, pointed to using the ca_dir option. When no ca_file or ca_dir is provided, the driver will use CAs provided by the native platform certificate store.

See mongoc_ssl_opt_t for more information on the various SSL related options.

Additional Connection Options

A variety of connection options for the MongoDB URI can be found here.