The out_mongo_replset Output plugin writes records into MongoDB, the emerging document-oriented database system.

This plugin is for users using ReplicaSet. If you are not using ReplicaSet, please see the out_mongo article instead.

This plugin has breaking changes since 0.8.0 due to mongo-ruby driver's breaking changes. If you are using prior 0.7.x series, please be careful to upgrade 1.0.0 or later versions.

Why Fluentd with MongoDB?

Fluentd enables your apps to insert records to MongoDB asynchronously with batch-insertion, unlike direct insertion of records from your apps. This has the following advantages:

1. less impact on application performance

2. higher MongoDB insertion throughput while maintaining JSON record

   structure

Install

out_mongo_replset is not included in td-agent by default. Fluentd gem users will need to install the fluent-plugin-mongo gem using the following command.

$ fluent-gem install fluent-plugin-mongo

Example Configuration

# Single MongoDB
<match mongo.**>
  @type mongo_replset
  database fluentd
  collection test
  nodes localhost:27017,localhost:27018,localhost:27019
​
  # The name of the replica set
  replica_set myapp
​
  <buffer>
    # flush
    flush_interval 10s
  </buffer>
</match>

Please see the Store Apache Logs into MongoDB article for real-world use cases.

Please see the Config File article for the basic structure and syntax of the configuration file. For <buffer> section, please check Buffer section cofiguration.

Parameters

type

The value must be mongo.

nodes

The comma separated node strings (e.g. host1:27017,host2:27017,host3:27017).

database

The database name.

collection

The collection name.

capped

This option enables capped collection. This is always recommended because MongoDB is not suited to storing large amounts of historical data.

capped_size

Sets the capped collection size.

user

The username to use for authentication.

password

The password to use for authentication.

tag_mapped

This option will allow out_mongo to use Fluentd's tag to determine the destination collection.

For example, if you generate records with tags 'mongo.foo', the records will be inserted into the foo collection within the fluentd database.

<match mongo.*>
  @type mongo_replset
  database fluentd
  nodes localhost:27017,localhost:27018,localhost:27019
​
  # Set 'tag_mapped' if you want to use tag mapped mode.
  tag_mapped
​
  # If the tag is "mongo.foo", then the prefix "mongo." is removed.
  # The inserted collection name is "foo".
  remove_tag_prefix mongo.
​
  # This configuration is used if the tag is not found. The default is 'untagged'.
  collection misc
</match>

replica_set

The name of the replica set.

read

The ReplicaSet read preference (e.g. secondary, etc).

num_retries

The ReplicaSet failover threshold. The default threshold is 60. If the retry count reaches this threshold, the plugin raises an exception.

Common Output / Buffer parameters

For common output / buffer parameters, please check the following articles.

• ​Output Plugin Overview​

• ​Buffer Section Configuration​

Further Readings

• ​fluent-plugin-webhdfs mongo​

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is a open source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.