Versions | v1.0 (td-agent3) | v0.12 (td-agent2)

MongoDB Output Plugin

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 doesn't describe all parameters. If you want to know full features, check the Further Reading section.

Table of Contents

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


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_size 1024m

  # authentication
  user michael
  password jordan

    # key name of timestamp
    time_key time

    # flush
    flush_interval 10s

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.



The value must be mongo.


type default version
string ‘localhost’ 1.0.0

The MongoDB hostname.

port (required)

type default version
integer 27017 1.0.0

The MongoDB port.


type default version
string required parameter 1.0.0

The database name.

collection (required, if not tag_mapped)

type default version
string ‘untagged’ or required parameter if not tag_mapped 1.0.0

The collection name.


type default version
string optional 1.0.0

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


type default version
size optional 1.0.0

Sets the capped collection size.


type default version
string nil 1.0.0

The username to use for authentication.


type default version
string nil 1.0.0

The password to use for authentication.


type default version
string time 1.0.0

The key name of timestamp. (default is “time”)


type default version
bool false 1.0.0

This option will allow out_mongo to use Fluentd’s tag to determine the destination collection. For example, if you generate records with tags ‘’, 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.

  # If the tag is "", 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

This option is useful for flexible log collection.

Common Output / Buffer parameters

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

Further Reading

Last updated: 2019-03-23 17:14:14 +0000

Versions | v1.0 (td-agent3) | v0.12 (td-agent2)

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.