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

If you're using ReplicaSet, please see the out_mongo_replset article instead.

This document does not describe all the parameters. For details, check the Further Reading section.

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 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

For more details, see Plugin Management.

Example Configuration

# Single MongoDB
<match mongo.**>
  @type mongo
  host fluentd
  port 27017
  database fluentd
  collection test
​
  # for capped collection
  capped
  capped_size 1024m
​
  # authentication
  user michael
  password jordan
​
  <inject>
    # key name of timestamp
    time_key time
  </inject>
​
  <buffer>
    # flush
    flush_interval 10s
  </buffer>
</match>

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

Please see the Configuration File article for the basic structure and syntax of the configuration file.

For <buffer>, refer to Buffer Section Configuration.

Parameters

@type

The value must be mongo.

connection_string (required)

The MongoDB connection string for URI.

host

The MongoDB hostname.

port (required)

The MongoDB port.

database (required)

The database name.

collection (required, if not tag_mapped)

The collection name.

capped

This option enables the capped collection. This is always recommended because MongoDB is not suited for 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.

time_key

The key name of timestamp.

tag_mapped

This option allows 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
  host fluentd
  port 27017
  database fluentd
​
  # 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>

This option is useful for flexible log collection.

Common Output / Buffer parameters

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

• ​Output Plugin Overview​

• ​Buffer Section Configuration​

Further Reading

• ​fluent-plugin-mongo​

If this article is incorrect or outdated, or omits critical information, please let us know.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