Procedure 8.10. To Install MongoDB on Each Host:

1. On a minimum of three hosts, install MongoDB and turn on the MongoDB service to make it persistent:

   # yum install -y mongodb-server mongodb
   # chkconfig mongod on

2. If you choose to install MongoDB using the basic install script provided, you must also delete the initial data from all but one installation to make it a part of the replica set. Stop the MongoDB service and delete the data using:

   # service mongod stop
   # rm -rf /var/lib/mongodb/*

Procedure 8.11. To Configure the MongoDB Service on Each Host:

1. Edit the /etc/mongodb.conf file and modify or add the following information:

   bind_ip = 0.0.0.0  # allow access from all interfaces
   auth = true
   rest = true
   smallfiles = true
   keyFile = /etc/mongodb.keyfile
   replSet = ose
   journal = true

   The following table provides a brief description of each setting from the example above.

   Table 8.1. Descriptions of /etc/mongodb.conf Settings

   Setting	Description
   bind_ip	This specifies the IP address MongoDB listens on for connections. Although the value must be an external address to form a replica set, this procedure also requires it to be reachable on the localhost interface. Specifying 0.0.0.0 binds to both.
   auth	This enables the MongoDB authentication system, which requires a login to access databases or other information.
   rest	This enables the simple REST API used by the replica set creation process.
   replSet	This names a replica set, and must be consistent among all the members for replication to take place.
   keyFile	This specifies the shared authentication key for the replica set, which is created in the next step.
   journal	This enables writes to be journaled, which enables faster recoveries from crashes.
   smallfiles	This reduces the initial size of data files, limits the files to 512MB, and reduces the size of the journal from 1GB to 128MB.

2. Create the shared key file with a secret value to synchronize the replica set. For security purposes, create a randomized value, and then copy it to all of the members of the replica set. Verify that the permissions are set correctly:

   # echo "sharedkey" > /etc/mongodb.keyfile
   # chown mongodb.mongodb /etc/mongodb.keyfile
   # chmod 400 /etc/mongodb.keyfile

3. Configure the firewall to allow MongoDB traffic on each host using the lokkit command:

   # lokkit --port=27017:tcp

   Red Hat Enterprise Linux provides different methods for configuring firewall ports. Alternatively, use iptables directly to configure firewall ports.
4. Start the MongoDB service on each host:

   # service mongod start

Procedure 8.12. To Form a Replica Set:

1. Authenticate to the admin database and initiate the ose replica set:

   # mongo
   > use admin
   switched to db admin
   
   > db.auth("admin", "password")
   1
   
   > rs.initiate()
   {
   	"info2" : "no configuration explicitly specified -- making one",
   	"me" : "mongo1.example.com:27017",
   	"info" : "Config now saved locally.  Should come online in about a minute.",
   	"ok" : 1
   }

2. Wait a few moments then press Enter until you see the ose:PRIMARY prompt. Then add new members to the replica set:

   ose:PRIMARY> rs.add("mongo2.example.com:27017")
   { "ok" : 1 }

   Repeat as required for all datastore hosts, using the FQDN or any resolvable name for each host.
3. Verify the replica set members:

   ose:PRIMARY> rs.status()
   {
   	"set" : "ose",
   	"date" : ISODate("2013-12-02T21:33:43Z"),
   	"myState" : 1,
   	"members" : [
   		{
   			"_id" : 0,
   			"name" : "mongo1.example.com:27017",
   			"health" : 1,
   			"state" : 1,
   			"stateStr" : "PRIMARY",
   			"uptime" : 1416,
   			"optime" : Timestamp(1386019903, 1),
   			"optimeDate" : ISODate("2013-12-02T21:31:43Z"),
   			"self" : true
   		},
   		{
   			"_id" : 1,
   			"name" : "mongo2.example.com:27017",
   			"health" : 1,
   			"state" : 2,
   			"stateStr" : "SECONDARY",
   			"uptime" : 120,
   			"optime" : Timestamp(1386019903, 1),
   			"optimeDate" : ISODate("2013-12-02T21:31:43Z"),
   			"lastHeartbeat" : ISODate("2013-12-02T21:33:43Z"),
   			"lastHeartbeatRecv" : ISODate("2013-12-02T21:33:43Z"),
   			"pingMs" : 1,
   			"syncingTo" : "mongo1.example.com:27017"
   		}
   	],
   	"ok" : 1
   }
   [...]
   

Procedure 8.13. To Configure the Broker Application to Use a Replica Set:

1. If you have not configured a MongoDB user named openshift to allow access to the broker host before forming the replica set as described in Chapter 7, Manually Installing and Configuring a Broker Host, add it now. Database changes at this point are synchronized among all members of the replica set.
2. Edit the /etc/openshift/broker.conf file on all broker hosts and set MONGO_HOST_PORT to the appropriate replica set members:

   # For replica sets, use ',' delimiter for multiple servers
   # Eg: MONGO_HOST_PORT="<host1:port1>,<host2:port2>..."
   MONGO_HOST_PORT="mongo1.example.com:27017,mongo2.example.com:27017,mongo3.example.com:27017"
   MONGO_USER="openshift"
   MONGO_PASSWORD="password"
   MONGO_DB="openshift_broker"