Stream Processing with Norikra
This article explains how to use Fluentd and Norikra to create a SQL-based realtime complex event processing platform.
​Fluentd is an advanced open-source log collector originally developed at Treasure Data, Inc. Fluentd is not only a log collector, but also an all-purpose stream processing platform. Plugins can be written to handle many kinds of events.
However, Fluentd is not primarily designed for stream processing. We must restart Fluentd after making modifications to its configuration/code, making it unsuitable for running both short-span (seconds or minutes) calculations and long-span (hours or days) calculations. If we restart Fluentd to perform a short-span calculation, all existing internal statuses of short and long span calculations are lost. For large scale stream processing platforms, code/processes must be added/removed without any such losses.
​Norikra is an open-source stream processing server based on Esper by EsperTech. It allows you to subscribe/unsubscribe to data streams anytime and add/remove SQL queries anytime. Norikra is written by @tagomoris, a committer of the Fluentd project.
This article will show you how to integrate Fluentd, Norikra, and the Fluentd norikra plugin to create a robust stream data processing platform.
The figure below shows the high-level architecture:
For the sake of simplicity, this guide will set up a one-node configuration. Please install the following on the same node:
​Fluentd​
​Fluentd Norikra Plugin​
​Norikra​
Fluentd can be installed through RubyGems or via deb/rpm packages.
​Debian Package​
​RPM Package​
​Ruby gem​
fluent-plugin-norikra can be installed with the gem install fluent-plugin-norikra (or fluent-gem) command.
Norikra requires JRuby. You can download the JRuby binary directly from the official site and export the PATH of JRUBY_INSTALL_DIRECTORY/bin.
Once JRuby is set up, install Norikra:
jgem install norikra
We'll start the Norikra server after installation. The norikra start command will launch the Norikra server in your console.
....2014-05-20 20:36:01 +0900 [INFO] : Loading UDF plugins2014-05-20 20:36:01 +0900 [INFO] : RPC server 0.0.0.0:26571, 2 threads2014-05-20 20:36:01 +0900 [INFO] : WebUI server 0.0.0.0:26578, 2 threads2014-05-20 20:36:01 +0900 [INFO] : Norikra server started.
You can also check the current Norikra's status via the WebUI (http://localhost:26578/).
We'll now configure Fluentd. If you used the deb/rpm package, Fluentd's config file is located at /etc/td-agent/td-agent.conf. Otherwise, it is located at /etc/fluentd/fluentd.conf.
For the input source, we will set up Fluentd to accept records from HTTP. The Fluentd configuration file should look like this:
<source>@type httpport 8888</source>
The output destination will be Norikra. The output configuration should look like this:
<match data.*>@type norikranorikra localhost:26571target_map_tag trueremove_tag_prefix data​<default>include *exclude time</default></match>
The <match> section specifies the glob pattern used to look for the matching tags. If the tag of a log is matched, the respective match configuration is used (i.e. the log is routed accordingly).
The norikra attribute specifies the Norikra server's RPC host and port (default: 26571). By target_map_tag true and remove_tag_prefix data, out_norikra handle the rest of tags (e.g. foo for data.foo) as the target, which is the name of the set of events as same as table name of RDBMS.
The <default> section specifies which fields are sent to the Norikra server. We can also specify these sets per target with <target NAME>...</target>. For more details, refer to fluent-plugin-norikra.
To test the configuration, just post the JSON to Fluentd (we use the curl command in this example):
$ curl -X POST -d 'json={"action":"login","user":2}' \http://localhost:8888/data.access
Norikra's console log will show that Fluentd has opened the target access and sent a message with fields of action and user.
2014-05-20 20:43:22 +0900 [INFO] : opening target, target:"access", fields:{}, auto_field:true2014-05-20 20:43:23 +0900 [INFO] : opening lazy target, target:#<Norikra::Target:0x69c04611 @last_modified=nil, @fields={}, @name="access", @auto_field=true>2014-05-20 20:43:23 +0900 [INFO] : target successfully opened (snip)
We can check its fields with norikra-client command from the console that has the PATH to JRuby:
$ norikra-client target listTARGET AUTO_FIELDaccess true1 targets found.$ norikra-client field list accessFIELD TYPE OPTIONALaction string falseuser integer false2 fields found.
We can add queries on opened targets via the WebUI or CLI. The following query (just SQL!) counts the number of events with a non-zero user per 10 second interval, with a 'group by' action:
SELECTaction,count(*) AS cFROM access.win:time_batch(10 sec)WHERE user != 0GROUP BY action
To register a query, issue norikra-client query add on the CLI:
$ norikra-client query add test_query "SELECT action, count(*) AS c FROM access.win:time_batch(10 sec) WHERE user != 0 GROUP BY action"$ norikra-client query listNAME GROUP TARGETS QUERYtest_query default access SELECT action, count(*) AS c FROM access.win:time_batch(10 sec) WHERE user != 0 GROUP BY action1 queries found.
Once the query has been registered, post the events that you want:
$ curl -X POST -d 'json={"action":"login","user":2}' \http://localhost:8888/data.access$ curl -X POST -d 'json={"action":"login","user":0}' \http://localhost:8888/data.access$ curl -X POST -d 'json={"action":"write","user":2}' \http://localhost:8888/data.access$ curl -X POST -d 'json={"action":"save","user":2}' \http://localhost:8888/data.access$ curl -X POST -d 'json={"action":"logout","user":2}' \http://localhost:8888/data.access$ curl -X POST -d 'json={"action":"logout","user":0}' \http://localhost:8888/data.access$ curl -X POST -d 'json={"action":"login","user":2}' \http://localhost:8888/data.access
And fetch output events from this test_query query:
$ norikra-client event fetch test_query{"time":"2014/05/20 21:00:24","c":1,"action":"logout"}{"time":"2014/05/20 21:00:24","c":1,"action":"save"}{"time":"2014/05/20 21:00:24","c":1,"action":"write"}{"time":"2014/05/20 21:00:24","c":2,"action":"login"}{"time":"2014/05/20 21:00:34","c":0,"action":"logout"}{"time":"2014/05/20 21:00:34","c":0,"action":"save"}{"time":"2014/05/20 21:00:34","c":0,"action":"write"}{"time":"2014/05/20 21:00:34","c":0,"action":"login"}$
If posts are done in 10 seconds, this query calculates all the events in first 10 seconds, and counts events per action for events with user != 0 only, and outputs events at "2014/05/20 21:00:24". At "2014/05/20 21:00:34", just after next 10 seconds, this query reports that no events arrived (These are teardown records, and reported only once).
We can create a stream data processing platform without any schema definitions, using Fluentd and Norikra. This platform enables an agile stream processing environment that can handle real workloads.
​Fluentd Architecture​
​Fluentd Get Started​
​Norikra: Query Syntax​
​Norikra: Query Examples​
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.
