To connect to a replica set, specify one or more members of the set and use
the "replicaSet" option. Multiple servers may be delimited
by a comma.
Example #1 ReplicaSet seedlist
// Using multiple servers as the seed list (prefered)
$m = new MongoClient("mongodb://rs1.example.com:27017,rs2.example.com:27017/?replicaSet=myReplSetName");
// Using one server as the seed list
$m = new MongoClient("mongodb://rs1.example.com:27017", array("replicaSet" => "myReplSetName"));
// Using multiple servers as the seed list
$m = new MongoClient("mongodb://rs1.example.com:27017,rs2.example.com:27017", array("replicaSet" => "myReplSetName"));
The PHP driver will query the database server(s) listed to determine the
primary. So long as it can connect to at least one host listed and find a
primary, the connection will succeed. If it cannot make a connection to any
servers listed or cannot find a primary, a
MongoConnectionException will be thrown.
You should always provide a seedlist with more than one member of the
ReplicaSet. For highest availability you should seed with at least one
server from each of your datacenters.
The host names that you specify here must match the
names as given in the replica set configuration because the driver uses the
name as specified in the replica set configuration as identifier in its
internal mapping. Specifying (for example) the IP address instead of the
configured host name makes that the driver keeps a connection for both the
host name and its accompanying IP address.
The driver does not support connecting to different
replica sets with the same name. This extends beyond one script so make
sure to have separate names for each of your replica sets. That also means
that you can not do this:
Example #2 Wrong replica set name duplication
$m = new MongoClient("mongodb://devserver1,devserver2,devserver3/?replicaSet=repset");
$m = new MongoClient("mongodb://prodserver1,prodserver2,prodserver3/?replicaSet=repset");
Instead, you need to have two different names for your replica sets:
Example #3 Correct use of two replica set names
$m = new MongoClient("mongodb://devserver1,devserver2,devserver3/?replicaSet=devset");
$m = new MongoClient("mongodb://prodserver1,prodserver2,prodserver3/?replicaSet=prodset");
If the primary becomes unavailable, an election will take place and a
secondary will be promoted to the role of primary (unless a majority vote
cannot be established). During this time
(» 20-60 seconds), the
connection will not be able to perform any write operations and attempts to
do so will result in an exception. Connections to secondaries will still be
able to perform reads.
The default Read Preference
is to only read from the primary. During the election process there is no
primary, and all read will therefore fail.
It is recommended to use
MongoClient::RP_PRIMARY_PREFERRED Read Preference for
applications that require high availability for reads, as reads will only
be executed on the secondaries when there simply isn't a primary
Once a primary is elected, attempting to perform a read or write will allow
the driver to detect the new primary. The driver will make this its primary
database connection and continue operating normally.
The health and state of a secondary is checked every 5 seconds
or when the next operation occurs after 5 seconds. It will also recheck
the configuration when the driver has a problem reaching a server.
Replica set failovers are checked every 60 seconds (configurable with
and whenever a write operation fails when using acknowledged writes.
Secondaries may be behind the primary in operations, so
your application must be able to handle out-of-date data when using
Read Preferences other then
For more information on replica sets, see the
» core documentation.
Added support for connecting to ReplicaSet and automatic failover.