Data Collection with Hadoop (HDFS)
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This article explains how to use 's to aggregate semi-structured logs into Hadoop HDFS.
is an advanced open-source log collector originally developed at . Fluentd is specifically designed to solve the big-data log collection problem. A lot of users are using Fluentd with MongoDB, and have found that it doesn't scale well for now.
HDFS (Hadoop) is a natural alternative for storing and processing a huge amount of data. It supports an HTTP interface called WebHDFS in addition to its Java library.
This article will show you how to use to receive data from HTTP and stream it into HDFS.
The figure below shows the high-level architecture:
The following software/services are required to be set up correctly:
Apache HDFS
For simplicity, this article will describe how to set up a one-node configuration. Please install the following software on the same node:
You can install Fluentd via major packaging systems.
If out_webhdfs (fluent-plugin-webhdfs) is not installed yet, please install it manually.
Let's start configuring Fluentd. If you used the deb/rpm package, Fluentd's config file is located at /etc/fluent/fluentd.conf.
For the input source, we will set up Fluentd to accept records from HTTP. The Fluentd configuration file should look like this:
The output destination will be WebHDFS. The output configuration should look like this:
The <match> section specifies the regexp used to look for matching tags. If a tag in a log is matched, the respective match configuration is used (i.e. the log is routed accordingly).
The flush_interval parameter specifies how often the data is written to HDFS. An append operation is used to append the incoming data to the file specified by the path parameter.
Placeholders for both time and hostname can be used with the path parameter. This prevents multiple Fluentd instances from appending data to the same file, which must be avoided for append operations.
Other options specify HDFS's NameNode host and port.
Append operations are not enabled by default. Please put these configurations into your hdfs-site.xml file and restart the whole cluster:
Please confirm that the HDFS user has the write access to the path specified as the WebHDFS output.
To test the configuration, just post the JSON to Fluentd (we use the curl command in this example). Sending a USR1 signal flushes Fluentd's buffer into WebHDFS:
We can then access HDFS to see the stored data:
()
For Cloudera CDH, please refer to the
See section how to install fluent-plugin-webhdfs on your environment.
Fluentd with WebHDFS makes the realtime log collection simple, robust and scalable! has already been using this plugin to collect 20,000 msgs/sec, 1.5 TB/day without any major problems for several months now.
If this article is incorrect or outdated, or omits critical information, please . is an open-source project under . All components are available under the Apache 2 License.
