ELK Stack Interview Questions

Elasticsearch permits you to store, search, and investigate enormous volumes of information rapidly including geospatial, organized, and unstructured and offer back responses in milliseconds. It utilizes a structure dependent on archives rather than tables and outlines and accompanies broad Rest APIs for putting away and analyzing the information. In this article, you can go through the set of frequently asked ELK Stack interview questions and answers in the interview panel. There will be questions for beginners, at intermediate level and of experienced level. This will help you crack the interview as the topmost industry experts curate these at HKR training.

Let us have a quick review of the ELK stack interview questions.

ELK Stack Interview Questions for Beginners:

1. The latest version of Elasticsearch.
The latest version was released in Jan 2020. It is a stable and updated version.

2. What is a replica?
Elasticsearch permits you to make at least one duplicate of your record's shards which are designated “replica shards” or just “replicas”. Replica shard is essentially a copy of the primary shard. Each archive in a file has a place with one essential shard. It gives excess duplicates of your information to secure against equipment failure and increase the ability to serve demands like searching or recovering a document.

3. The configuration management tools that are supported by Elasticsearch.
Ans:Ansible, Chef and Puppet

4. Define Shard.
Elasticsearch gives the capacity to partition the file into various pieces called shards. Every shard is in itself a completely practical and free index which can be facilitated on any particular node inside a cluster. Circulates the reports in a list over various shards, and appropriates those shards over numerous nodes. Elasticsearch guarantees repetition that ensures against equipment failure and builds inquiry limits as nodes are being added to the cluster. 

5. What is ELK Stack?
The ELK Stack is an assortment of three open-source items, Elasticsearch, Logstash, and Kibana. They are completely evolved and kept up by the organization Elastic.

6. How will you delete an index?
You can use the command DELETE/index name to delete an index. 

7. Explain Ingest nodes.
The ingest node is utilized to change the file prior to indexing it in Elasticsearch. Fundamentally, an ingest node  pre-measure the file before indexing happens. Such tasks like renaming a field name, adding or eliminating a field from a record are taken care of by the ingest node.

8. What is Apache Lucene?
Apache Lucene is an open-source data recovery programming library written in Java language. 

9. Single document APIs in Elasticsearch.

  • Get API
  • Index API
  • Delete API
  • Update API

10. Define Tokenizer.
Tokenizer could break down documents which estimates of a report into a flow. Inverted indexes are made and refreshed by utilizing these values. From that point onward, the streams of values  are put away in the report. 

11. What is fuzzy search?
Fluffy search is a cycle where web page record locations ought to be distinguished. It resembles the search keyword. It additionally works when the argument isn't applicable to the search reporter for specific data. 

12. Explain mapping.
Mapping is a cycle which assists you characterize how a report is mapped to the web search engine. Its searchable attributes are incorporated fields and are tokenized as accessible. 

13. Define NRT.
NRT or Near Real-Time Search  platform implies there is a slight dormancy (generally one second) from when you list a report until it turns out to be truly accessible and searchable.

14. Define what a Cluster is.
It is a gathering of at least one node instances that are linked together. The intensity of an Elasticsearch group lies in the appropriation of errands, tasks, analyzing, and ordering all the nodes of the cluster.

15. Define Elasticsearch.
Elasticsearch is a dispersed, open source search and investigation engine constructed on Apache Lucene and created in Java. It began as a versatile adaptation of the Lucene open-source search structure that added the capacity to evenly scale Lucene files.

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ELK Stack Interview Questions for Intermediate:

1. Explain ELK Stack Architecture.
ELK Stack is intended to permit clients to take in information from any source, in any layout, and to investigate, search and visualize that information continuously. ElasticSearch is utilized for storing logs. LogStash is utilized for both delivery, processing and putting away logs. Kibana is a visualization tool which is facilitated through Nginx or Apache. 

  • Logs: Server logs that should be analyzed are distinguished 
  • Logstash: Collect the logs and instances information. It alters the information. 
  • ElasticSearch: The changed information from Logstash is searched, stored and indexed. 
  • Kibana: Kibana utilizes Elasticsearch DB to share, explore and visualize.

2. Where do you store Elasticsearch?
Elastic search results are put away in a distributed document in various catalogs. Additionally, a client can recover complex information structures which are serialized as JSON documents. 

3. Programming languages and text languages used in Elasticsearch.
Elasticsearch backs up a variety of programming languages like Ruby, Java, PHP, JavaScript (Node.js), Python, Go, .NET (C#),and  Perl. It also supports 34 text dialects, varying from Arabic language to Thai, and gives analyzers for each. Backing for extra dialects can be added with custom plugins.

4. How does Elasticsearch work?
Raw information streams into Elasticsearch from an assortment of sources, consisting of logs, web applications, and framework metrics. Information ingestion is the cycle by which information is parsed, standardized, and enhanced before it is listed in Elasticsearch. Clients can run complex questions against their information and use collections to recover complex synopses of their information once filed in Elasticsearch.

5. What are Inverted indexes?
Inverted index is the core of web crawlers. The essential objective of a search engine is to give quick inquiries while finding the reports where search terms happen. It is a hashmap like information structure which guides clients from a word to a record or a website page. 

6. What are Migration APIs?
Migration API is put in after the Elasticsearch version is redesigned with a more up to date version. Using the migration API, X-Pack lists get refreshed into a more current version of the Elasticsearch cluster. 

7. Define Elasticsearch Data Node.
Elasticsearch Data nodes hold shards which manage indexed files. They assist you with executing information related to CRUD and search aggregation activities and so on. In any case, you are required to Set node.data=true to create the node as a Data Node.

8. Explain Aggregations.
Elasticsearch gives an aggregation API, that is utilized for the assemblage of information. The structure gives accumulated information dependent on the query. Aggregation system gathers all the information that is chosen by the pursuit query and delivers to the client. It includes a few structures that help to fabricate an unpredictable synopsis of data. It produces the logical data accessible in Elasticsearch. 

9. What are the different commands accessible in Elasticsearch cat API?
These commands acknowledge a query string parameter. This assists with seeing all data and headers and information they give and the/_cat command, which permits you to record all the accessible commands. Command utilizing with cat API are: 

  • Cat health, cat indices, cat master, pending tasks, cat plugins, cat recovery
  • Cat aliases, cat allocation, cat count, cat fielddata
  • Cat repositories, cat snapshots, cat templates

10. Define Dynamic Mapping.
Dynamic planning encourages the client to index files without undesirable configuration for the field name. It can be added naturally through the Elasticsearch for certain custom guidelines. 

11. Define the filters in Elasticsearch.
A Filter is tied in with actualizing a few conditions in the inquiry to lessen the coordinating outcome set. At the point when we utilize a query in Elasticsearch and it processes a pertinence score for coordinating the records. We needn't require scores when the archive falls in the scope of two given timestamps. We utilise Filters for coordinating specific models, and they are cacheable to permit quicker execution. The Token channels get a progression of tokens from a tokenizer, and they can add, change, and erase the tokens. 

12. What are the X- Pack Commands?
X-Pack commands which will aid you in configuring security:

  • migrate
  • saml-metadata
  • certutil
  • syskeygen
  • users
  • certgen
  • setup-passwords

13. Explain Query DSL in Elasticsearch.
Elasticsearch provides a full Query DSL (Domain Specific Language) oriented on JSON to define queries.

14. What are the documents accessible in ElasticSearch?
The document is fundamentally the same as a row in relational databases. Each report in the index has a diverse structure however has a similar data type for particular fields. 

MySQL => Databases => Tables => Columns/Rows 

ElasticSearch => Indices => Types => Documents with Properties

15. Explain the main functions executed on a document.
Documents are the essential unit of data that can be ordered in Elasticsearch communicated in JSON, which is the worldwide web information trade design. It can be something other than text, like numbers, strings, and dates, it tends to be any organized information encoded in JSON. Each report has an exceptional ID and a given information type.

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ELK Stack Interview Questions for Experienced:

1. Characteristics of Elasticsearch.

  • It is an open-source search server  composed utilizing Java. 
  • Full-Text Search.
  • Used to list any sort of heterogeneous information. 
  • Near Real-Time (NRT) search.
  • Multi-language and Geolocation uphold.
  • Sharded, duplicated accessible, JSON archive store. 
  • Has REST API web-interface with JSON output.
  • Schema free, REST and JSON oriented distributed document store 

2. Explain the use of restore APIs.
Elasticsearch gives a restore API to reestablish the information that is backed up to an image. Thus, the restore API assists with reestablishing a snapshot into a running group. To reestablish the information into Elasticsearch, both _snapshot and _restore APIs are utilized alongside the snapshot name that you need to reestablish. For instance, POST/_snapshot/snapshot_name/_restore

3. What is filebeat?
Filebeat is utilized to indicate the delivery of the log documents or log information. It is intended to assume the logging specialist's job, which is introduced on the machine creating the log records, following them, and sending the information to either Logstash for advanced handling or straightforwardly into Elasticsearch for listing. 

4. Explain the Analyzers in Elasticsearch
While ordering information in ElasticSearch, information is moved inside by the Analyzer characterized for the index, and afterwards listed. An analyzer is a collection of filters and tokenizers. Analyzers accessible in ElasticSearch 1.10 are given below:

  • Custom Analyzer
  • WhiteSpace Analyzer
  • Simple Analyzer
  • Keyword Analyzer
  • Pattern Analyzer
  • Stop Analyzer
  • Language Analyzer
  • Standard Analyzer
  • Snowball Analyzer

5. Define the term Index.
Elasticsearch index is an assortment of reports that are identified with one another. It stores information as JSON archives or documents. Each report relates a bunch of keys consisting of the name  full-text analysis. It records each extraordinary word that shows up in any report and recognizes the entirety of the archives that each word has. In this method,  it stores records and assembles an inverted index to make the archive information accessible. Indexing begins with the file API, with which a JSON report in a particular file is added or refreshed. The index is like an information base in a social data set pattern. Any records in a list are ordinarily legitimately related. This can be distinguished by a name that is utilized to allude to the list while performing ordering, search, update, and erase activities against the archives in it.

6. Explain the purpose of utilizing ELK Stack

  • It gives astounding experiences to this single instance  and furthermore deletes the requirement to sign into a hundred diverse log information sources. 
  • Simple to send Scales horizontally and vertically.
  • ELK functions accurately when logs from different Apps of an undertaking merge into a solitary ELK instance.
  • Fast on-premise establishment 
  • Accessibility of libraries for various programming and scripting languages
  • Elastic provides a large group of language customers, which incorporates Python, Ruby, PHP, .NET, Perl, Java, and JavaScript.

7. What is pagination is Elasticsearch?
Elasticsearch tools permit clients to use the method of pagination. With the assistance of pagination, we can get a particular number of records to be given back to the clients.

The two properties in Elasticsearch called “from” and “size”, that aids to do pagination productively. The measures are given below,

  • From - The property is utilized to determine the beginning so that each page can be searched through the documents in the file. It determines from where Elasticsearch should begin its query. Characterizing the quantity of items that is required to be neglected from the beginning is also possible. It defaults to 0.
  • Size - The property is utilized to determine the quantity of records in a page supposed to undergo a search. It implies how much outcome it will return. It defaults to 10.

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8. Explain Logstash.
Logstash is the item in ELK which is known as the data pipeline apparatus. It is explicitly intended to perform tasks like gathering, storing, and parsing the logs for sometime later. It is an open-source information assortment engine fit for binding together the information from numerous resources and normalizing it. Logstash additionally assists in assorted downstream investigation for business upgrades.

9. Benefits of Elasticsearch

  • Assist you to scale horizontally and vertically.
  • Oriented on Apache Lucene and gives RESTful APIs.
  • Control your information record by record with the assistance of Multi- document APIs 
  • It gives dependability, horizontal scalability, and multi-tenant ability for ongoing utilization of indexing. 
  • Perform filtering and questioning your information for insights.
  • Store pattern less information and furthermore makes a schema for your information.

10. Explain Index Lifecycle Management in Elasticsearch
Index Lifecycle Management (ILM) is a basic component of Elasticsearch, which has been presented in Elasticsearch 6.6. ILM sets up a hot-warm-cool design that provides a lifecycle to the file. This has four states: Hot, Warm, Cold, and Delete state. Ordinarily, ILM deals with the indexes and their activities. Elasticsearch provides the ILM APIs for dealing with the records. Index Management API, Policy Management API, and Operation Management API are the Index Lifecycle Management APIs. These APIs also provide APIs to its clients to deal with the indexes.

11. What are the query languages in ElasticSearch?
Elasticsearch gives a query DSL(Domain Specific Language) based on JSON for characterizing the queries. Query DSL includes two sorts of clauses: 

  • Leaf Query Clauses : Leaf Query Clauses look for a particular incentive in a particular field, similar to the term, reach, or match inquiries. 
  • Compound Query Clauses : Compound Query Clauses encase other compounds or leaf questions, and we utilise them for consistently consolidating inquiries.

12. What are the use cases that are related to ELK log analytics?
The use cases of ELK log analytics are given below:

  • E-commerce Search solution
  • Market Intelligence
  • Security analysis
  • Fraud detection
  • Compliance
  • Risk management

13. Explain the methods of searching in Elasticsearch.
There are three potential manners by which we can execute search in Elasticsearch. They are given below:

  • Search utilizing Query DSL (Domain Specific language ) inside the body: The DSL language is utilized for the JSON demand body. 
  • Applying search API across various files and numerous types: We can execute the quest activity for a substance across the various types and lists utilizing the search API. 
  • Search request utilizing a Uniform Resource Identifier: This activity is executed utilizing a special identifier called a Uniform Resource Identifier.

14. What are nodes in Elasticsearch.
Node is an instance of Elasticsearch. There are various sorts of nodes that are given below: 

  • Client nodes: Client nodes are the nodes which are approved to deploy the cluster demands to the master node and the information demands to the data nodes.
  • Data nodes: Data nodes are the nodes which contain the information that assists in executing functions like make, read, refresh and erase, search, and aggregations on the information.
  • Ingest nodes: Ingest nodes are the nodes which aids in pre-processing the reports prior to executing indexing.
  • Master nodes: Master nodes are the nodes which assists in handling and designing the information to add and eliminate the nodes to the cluster as needed.

15. What are the characteristics of Aggregations?

  • Utilizing aggregation in elasticsearch, can perform GROUP BY aggregation on any numeric field, yet we should type keywords or there must be fielddata = valid for text fields.
  • It tends to be considered as a single unit-of-work that makes analytic data over a bunch of archives which are accessible in elasticsearch. 
  • It is fundamentally based on the building blocks. 
  • It can be formed together to manufacture complex sum up of information. 
  • Aggregation functions are the same as GROUP BY COUNT and SQL AVERAGE functions.


We trust that this set of ELK Stack interview questions and answers for freshers and experienced experts will assist you in planning for your interviews. We attempted to cover all the questions. On the off chance that you locate any related question that is not here, kindly offer that in the comment section and we will add it at the earliest.

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