Logstash Interview Questions and Answers


Logstash Interview Questions and answers have been framed specially to get you prepared for the most frequently asked questions in many job interviews. Here we have provided Tips and Tricks for cracking LogStash interview Questions. These LogStash Interview questions and answers are useful for Beginner, Advanced Experienced programmers and job seekers of different experience levels.


Question 1. What is Logstash?

Answer: Logstash is an open source data collection engine with real-time pipelining capabilities. Logstash can dynamically unify the data from disparate sources and normalize the data into destinations of your choice. Cleanse and democratize all your data for diverse advanced downstream analytics and visualization use cases.

Question 2. What is the Architecture of Logstash?

Answer:  The Logstash occasion handling pipeline has three phases

inputs → filters → outputs.

Inputs produce events, filters adjust them, and output sends them somewhere else. Inputs and outputs bolster codecs that empower you to encode or disentangle the information as it enters or leaves the pipeline without utilizing a different channel.

Information is regularly dispersed or soloed across numerous frameworks in numerous configurations. Logstash underpins an assortment of data sources that pull in occasions from a large number of regular sources, all simultaneously. Effectively ingest from your logs, metrics, web applications, information stores, and different AWS services, all in constant, gushing style.


As information goes from source to store, Logstash channels parse every occasion, distinguish named fields to fabricate the structure, and change them to combine on a typical organization for all the more dominant investigation and business esteem.

Logstash powerfully changes and readies your information paying little heed to format or complexity:

  • Get structure from unstructured information with grok.
  • Interpret geo coordinates from IP addresses.
  • Anonymize PII information, bar delicate fields totally.
  • Easy handling, free of the data source, format, or schema.

Question 3. What is Logstash used for?

Answer: Logstash is an open source tool for collecting, parsing, and storing logs for future use. Kibana 3 is a web interface that can be used to search and view the logs that Logstash has indexed. Both of these tools are based on Elastic search.

Question 4. What Does Logstash Forwarder Do?

Answer: File beat is based on the Logstash Forwarder source code and replaces Logstash Forwarder as the method to use for tailing log files and forwarding them to Logstash. The registry file, which stores the state of the currently read files, was changed.

Question 5. What Is ELK Stack (elastic Stack)?

Answer: Elastic search, Logstash, and Kibana, when used together is known as an ELK stack.

 Question 6. What Is The Power Of Logstash?

Answer:  Logstash has below powers:-

1) The ingestion workhorse for Elastic search and more – Horizontally scalable data processing pipeline with strong Elastic search and Kibana synergy.

2) Pluggable pipeline architecture – Mix, match, and orchestrate different inputs, filters, and outputs to play in pipeline harmony.

3) Community-extensible and developer-friendly plugin ecosystem – Over 200 plugins available, plus the flexibility of creating and contributing your own.

Question 7. What Are Logs And Metrics In Logstash?

Answer: Logstash has below Logs and Metrics:-

  • Logs and Metrics – Logstash handle all types of logging data.
  • Easily ingest a multitude of web logs like Apache, and application logs like log4j for Java.s
  • Capture many other log formats like syslog, networking and firewall logs, and more.
  • Enjoy complimentary secure log forwarding capabilities with File beat.
  • Collect metrics from Ganglia, collected, NetFlow, JMX, and many other infrastructure and application platforms over TCP and UDP.

Question 8. How Does Logstash Work With The Web?

Answer:  Logstash transform HTTP requests into events:

  • Consume from web service firehouses like Twitter for social sentiment analysis.
  • Web hook support for GitHub, Hip Chat, JIRA, and countless other applications.
  • Enables many Watcher alerting use cases.
  • Create events by polling HTTP endpoints on demand.
  • Universally capture health, performance, metrics, and other types of data from web application interfaces.
  • Perfect for scenarios where the control of polling is preferred over receiving.

Question 9. Which Java Version Is Required To Install Logstash?

Answer:  Logstash requires Java 8. Java 9 is not supported.

Question 10. What Are The Two Required Elements In Logstash Pipeline?

Answer:  A Logstash pipeline has two required elements, input and output, and one optional element, filter. The input plugins consume data from a source, the filter plugins modify the data as you specify, and the output plugins write the data to a destination.

 Question 11. What Is File Beat?

Answer:  The File beat client is a lightweight, resource-friendly tool that collects logs from files on the server and forwards these logs to your Logstash instance for processing.

File beat is designed for reliability and low latency. File beat has a light resource footprint on the host machine, and the Beats input plugin minimizes the resource demands on the Logstash instance.

 Question 12. What Is Grok Filter Plugin?

Answer:  The grok filter plugin enables you to parse the unstructured log data into something structured and query able. Because the grok filter plugin looks for patterns in the incoming log data, configuring the plugin requires you to make decisions about how to identify the patterns that are of interest to your use case.

Question 13. What Is Geoip Plugin?

Answer:  Geoip plugin looks up IP addresses, derives geographic location information from the addresses, and adds that location information to the logs.

Question 14. How Do You Read Data From A Twitter Feed?

AnswerTo add a Twitter feed, you use the twitter input plugin. To configure the plugin, you need several pieces of information:

  • A consumer key, which uniquely identifies your Twitter app.
  • A consumer secret, which serves as the password for your Twitter app.
  • One or more keywords to search in the incoming feed. The example shows using “cloud” as a keyword, but you can use whatever you want.
  • An oauth token, which identifies the Twitter account using this app.
  • An oauth token secret, which serves as the password of the Twitter account.

Question 15. Can You Explain How Logstash Works?

AnswerThe Logstash event processing pipeline has three stages:

inputs -> filters -> outputs.

Inputs generate events, filters modify them, and outputs ship them elsewhere. Inputs and outputs support codecs that enable you to encode or decode the data as it enters or exits the pipeline without having to use a separate filter.

Question 16. What Are Inputs In Logstash?

Answer:  You use inputs to get data into Logstash.

Some of the more commonly-used inputs are:

  • File
  • Syslog
  • Redis
  • Beats
  • File:reads from a file on the filesystem, much like the UNIX command tail -0F
  • Syslog:listens on the well-known port 514 for syslog messages and parses according to the RFC3164 format
  • Redis:reads from a redis server, using both redis channels and redis lists. Redis is often used as a “broker” in a centralized Logstash installation, which queues Logstash events from remote Logstash “shippers”.
  • Beats:processes events sent by File beat.

Question 17. What Are Filters In Logstash?

Answer: Filters are intermediary processing devices in the Logstash pipeline. You can combine filters with conditionals to perform an action on an event if it meets certain criteria.

Some useful filters include:

  • Grok:parse and structure arbitrary text. Grok is currently the best way in Logstash to parse unstructured log data into something structured and query able. With 120 patterns built-in to Logstash, it’s more than likely you’ll find one that meets your needs!
  • Mutate:perform general transformations on event fields. You can rename, remove, replace, and modify fields in your events.
  • Drop:drop an event completely, for example, debug events.
  • Clone:make a copy of an event, possibly adding or removing fields.
  • Geoip:add information about geographical location of IP addresses (also displays amazing charts in Kibana!)

Question 18. What Are Outputs In Logstash?

Answer: Outputs are the final phase of the Logstash pipeline. An event can pass through multiple outputs, but once all output processing is complete, the event has finished its execution.

Some commonly used outputs include:

  • Elastic search:send event data to Elastic search. If you’re planning to save your data        in an efficient, convenient, and easily query able format.
  • File:write event data to a file on disk.
  • Graphite:send event data to graphite, a popular open source tool for storing and   graphing metrics.
  • Statsd:send event data to statsd, a service that “listens for statistics, like counters and timers, sent over UDP and sends aggregates to one or more pluggable backend services”. If you’re already using statsd, this could be useful for you!

Question 19. What Are Codecs In Logstash?

Answer:  Codecs are basically streamed filters that can operate as part of an input or output. Codecs enable you to easily separate the transport of your messages from the serialization process. Popular codecs include json, msgpack, and plain (text).

Json: encode or decode data in the JSON format.

Multiline: merge multiple-line text events such as java exception and stack trace messages into a single event.

Question 20. Explain The Execution Model Of Logstash?

Answer: 1) The Logstash event processing pipeline coordinates the execution of inputs, filters, and outputs.

2) Each input stage in the Logstash pipeline runs in its own thread. Inputs write events to a central queue that is either in memory (default) or on disk.

3) Each pipeline worker thread takes a batch of events off this queue, runs the batch of events through the configured filters, and then runs the filtered events through any outputs.

Question 21. How Many Types Of Logstash Configuration Files Are There?

Answer: Logstash has two types of configuration files: pipeline configuration files, which define the Logstash processing pipeline, and settings files, which specify options that control Logstash startup and execution.

We hope, this post will help you a lot. Please leave a comment if you want to update any answer or want to add any new question.

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