AerisCloud.mongodb

MongoDB Role

Configuration

[mongodb:children]
mongodb-somedc-prod

[mongodb-somedc-prod:children]
mongodb1-somedc-prod

[mongodb1-somedc-prod]
mongodb1.somedc.prod ansible_ssh_host=172.16.0.210
mongodb2.somedc.prod ansible_ssh_host=172.16.0.211
mongodb3.somedc.prod ansible_ssh_host=172.16.0.212

[mongodb1-somedc-prod:vars]
# Where MongoDB data will be stored (default: /var/lib/mongodb)
mongodb_data_path = /data/mongodb

# Should we use smallfiles? (default: false)
# http://docs.mongodb.org/manual/reference/configuration-options/#storage.smallFiles
mongodb_smallfiles = false

# Enables the durability journal to ensure data files remain valid and recoverable.
# http://docs.mongodb.org/manual/reference/configuration-options/#storage.journal.enabled
mongodb_nojournal = false

# It **MUST** be the name of the inventory group containing all the servers of your replica set.
mongodb_replica_set_name = mongodb1-somedc-prod

# Specifies a maximum size in megabytes for the replication operation log.
# Once the mongod has created the oplog for the first time,
# changing this option will not affect the size of the oplog.
# You have to follow [this procedure](http://docs.mongodb.org/manual/tutorial/change-oplog-size/) to change it.
# http://docs.mongodb.org/manual/reference/configuration-options/#replication.oplogSizeMB
# http://docs.mongodb.org/manual/core/replica-set-oplog/#replica-set-oplog-sizing
mongodb_oplog_size = 1024

Bootstrapping a Replica Set

To bootstrap a replica set, you need to add the mongodb_bootstrap variable with the name of of one of the members of the replica set.

Example:

ansible-playbook playbook.yml \
  --limit="mongodb" \
  --extra-vars="mongodb_bootstrap=node1.mongodb1.*"

Notes:

The value of mongodb_bootstrap must be the name of one of the replica set members.
All the servers of the replica set must have mongodb_replica_set_name defined to the same value.

Replication

The minimum requirements for a replica set are: A primary, a secondary, and an arbiter. Most deployments, however, will keep three members that store data: A primary and two secondary members.

Arbiters

If you have an even number of servers, you need to define an arbiter, otherwise the election won't happen. Arbiters do not keep a copy of the data. However, arbiters play a role in the elections that select a primary if the current primary is unavailable. Do not run an arbiter on systems that also host the primary or the secondary members of the replica set.

Read Preference

All members of the replica set can accept read operations. However, by default, an application directs its read operations to the primary member. See Read Preference for details on changing the default read behavior.