Provided by: libmongoc-doc_1.16.1-1build2_all 
NAME
mongoc_advanced_connections - 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/bson.h>
#include <mongoc/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;
}
TIP:
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.
WARNING:
Specifying the replicaSet parameter when connecting to a mongos sharding server is
invalid.
#include <bson/bson.h>
#include <mongoc/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 WITH IPV4 AND IPV6
If connecting to a hostname that has both IPv4 and IPv6 DNS records, the behavior follows
RFC-6555. A connection to the IPv6 address is attempted first. If IPv6 fails, then a
connection is attempted to the IPv4 address. If the connection attempt to IPv6 does not
complete within 250ms, then IPv4 is tried in parallel. Whichever succeeds connection first
cancels the other. The successful DNS result is cached for 10 minutes.
As a consequence, attempts to connect to a mongod only listening on IPv4 may be delayed if
there are both A (IPv4) and AAAA (IPv6) DNS records associated with the host.
To avoid a delay, configure hostnames to match the MongoDB configuration. That is, only
create an A record if the mongod is only listening on IPv4.
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. Pass the URL-encoded path to the socket, which must be suffixed with .sock.
For example, to connect to a domain socket at /tmp/mongodb-27017.sock:
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://%2Ftmp%2Fmongodb-27017.sock");
Include username and password like so:
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://user:pass@%2Ftmp%2Fmongodb-27017.sock");
CONNECTING TO A SERVER OVER SSL
These are instructions for configuring TLS/SSL connections.
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");
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_opt_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 concatenated 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.
COMPRESSING DATA TO AND FROM MONGODB
MongoDB 3.4 added Snappy compression support, zlib compression in 3.6, and zstd
compression in 4.2. To enable compression support the client must be configured with
which compressors to use:
mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?compressors=snappy,zlib,zstd");
The compressors option specifies the priority order of compressors the client wants to
use. Messages are compressed if the client and server share any compressors in common.
Note that the compressor used by the server might not be the same compressor as the client
used. For example, if the client uses the connection string compressors=zlib,snappy the
client will use zlib compression to send data (if possible), but the server might still
reply using snappy, depending on how the server was configured.
The driver must be built with zlib and/or snappy and/or zstd support to enable compression
support, any unknown (or not compiled in) compressor value will be ignored. Note: to build
with zstd requires cmake 3.12 or higher.
ADDITIONAL CONNECTION OPTIONS
The full list of connection options can be found in the mongoc_uri_t docs.
Certain socket/connection related options are not configurable:
┌──────────────┬──────────────────────────┬────────────────────────┐
│Option │ Description │ Value │
├──────────────┼──────────────────────────┼────────────────────────┤
│SO_KEEPALIVE │ TCP Keep Alive │ Enabled │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_KEEPIDLE │ How long a connection │ 300 seconds │
│ │ needs to remain idle │ │
│ │ before TCP starts │ │
│ │ sending keepalive probes │ │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_KEEPINTVL │ The time in seconds │ 10 seconds │
│ │ between TCP probes │ │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_KEEPCNT │ How many probes to send, │ 9 probes │
│ │ without acknowledgement, │ │
│ │ before dropping the │ │
│ │ connection │ │
├──────────────┼──────────────────────────┼────────────────────────┤
│TCP_NODELAY │ Send packets as soon as │ Enabled (no buffering) │
│ │ possible or buffer small │ │
│ │ packets (Nagle │ │
│ │ algorithm) │ │
└──────────────┴──────────────────────────┴────────────────────────┘
AUTHOR
MongoDB, Inc
COPYRIGHT
2017-present, MongoDB, Inc