Elastic Search interview questions for experienced/Elastic search Interview Questions and Answers for Freshers & Experienced

What is Ingest Node in Elasticsearch?

The ingest node is used to transform the document before indexing it in Elasticsearch. Basically, an ingest node pre-process the document before the indexing occurs. Such operations like rename a field name, add or remove a field from a document are handled by the ingest node.

How x-pack helps to get SQL access in Elasticsearch?

X-pack comes with the SQL features that provide SQL access in Elasticsearch to execute the queries. This SQL support feature has been introduced in Elasticsearch 6.3.

Basically, X-pack is an Elastic Stack extension with SQL features, which helps the users to execute the SQL queries against Elasticsearch. The SQL queries execute in a real-time environment and return the result in tabular form.

Can we perform the write operation on frozen indices?

No, we cannot perform a write operation on frozen indices because frozen indices are read-only indices. These indices are searchable, but we cannot write on them without unfreezing. However, without unfreezing the frozen indices, we can include them in our searches.

Is Elasticsearch can integrate with other tools? If Yes, then list the name of those tools?

Yes, Elasticsearch can integrate with other tools and technologies. The most popular tools are Logstash and Kibana, which are the components of the ELK stack. There is a list of some other tools to which Elasticsearch can integrate -

Amazon Elasticsearch Services
Couchbase
Contentful
Datadog

To install the Elasticsearch, which type of files are required to be download on different operating systems?

On each operating system, a different type of file is required to be downloaded.

For example -

* On Windows operating system, zip file needs to be download. Similarly,
* On Linux operating system, download tar.gz file of Elasticsearch setup
* On Mac Operating system, download tar.gz file of Elasticsearch setup
* For Ubuntu-based system or Debian, download the deb package

What is from and size components in Elasticsearch?

The from and size components are used in pagination. They help to divide a large amount of data into several pages, where from is the initial point to start a search and size defines the number of items to be searched.

For example, - If there are 30 items calculated, but we want 15 items first and then remaining.

So, the first time from will be 0 and the size will be 14. Next time from will be 15 and the size will be 29.

What is a document type in Elasticsearch?

In Elasticsearch, a type represents a class of similar documents. A type could be like student, customer, or item. A document type can be seen as the document schema/mapping, which has a mapping of all the fields in the document along with its data type.

What is the query language of ElasticSearch?

Elasticsearch provides a query DSL(Domain Specific Language) on the basis of JSON for defining the queries. Query DSL contains two kinds of clauses:

1) Leaf Query Clauses

Leaf Query Clauses search for a specific value in a specific field, like the term, range, or match queries.

2) Compound Query Clauses

Compound Query Clauses enclose other compound or leaf queries, and we use them for logically combining queries.

What is a Filter in ElasticSearch?

A Filter is all about implementing some conditions in the query to reduce the matching result set. When we use a query in Elasticsearch, the query computes a relevance score for matching the documents. But in some situations, we don’t need relevance scores when the document falls in the range of two provided timestamps.

So, for this yes/no criteria, we use Filters. We use Filters for matching particular criteria, and they are cacheable to allow faster execution. The Token filters receive a flow of tokens from a tokenizer, and they can change, add, and delete the tokens.

What is indexing in ElasticSearch?

The process of storing data in an index is called indexing in ElasticSearch. Data in ElasticSearch can be divided into write-once and read-many segments. Whenever an update is attempted, a new version of the document is written to the index.

Can you please list use cases related to ELK log analytics?

ELK log analytics successfully designed use cases are listed below:

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

What is a document in ElasticSearch?

A document is similar to a row in relational databases. The difference is that each document in an index can have a different structure (fields), but should have the same data type for common fields.Each field can occur multiple times in a document with different data types. Fields can contain other documents too.

How Elastic Stack Reporting is used?

Reporting API helps to retrieve data in PDF format, image PNG format as well as spreadsheet CSV format and can be shared or saved as per need.

How Log stash can be used with Elasticsearch?

Log stash is an open-source ETL server-side engine that comes along with ELK Stack that collects, and processes data from a large variety of sources.

What is Elasticsearch Data Node?

Data nodes hold shards that handle indexed documents. They help you to execute data related CRUD and search aggregation operations etc. However, you need to Set node.data=true to make node as Data Node.

What is Query DSL in Elasticsearch?

Elasticsearch offers full Query DSL (Domain Specific Language) based on JSON to define queries.

Which method is used to fetch the documents from Elasticsearch?

Elasticsearch allows the users to search and fetch the documents from the database in two ways. We can use one of them accordingly -

* By sending a GET request having a string parameter with a query, or
* By sending a POST request which has a query in request body.

Along with the request method, we have to use a __search API to search the documents in database. Here GET and POST are request methods. Elasticsearch allows the users to search the documents as single or in bulk too.

What is the importance of installing X-Pack for Elasticsearch?

X-Pack is an extension that gets installed with Elasticsearch. Some of the functionalities of X-Pack are security (Roles and User security, Role-based access, Privileges/Permissions), monitoring, alerting, reporting, and more.

What is the functionality of cat API in Elasticsearch?

Cat API commands provide an overview of the Elasticsearch cluster including data related to aliases, allocation, indices, node attributes, etc. These cat commands use query string as a parameter that returns queried data from the JSON document.

How Beats can be used with Elasticsearch?

Beats is an open-source tool used to transfer data to Elasticsearch where data is processed before being viewed using Kibana. Data such as audit data, log files, window event logs, cloud data, and network traffic are transported.

Can you please explain the functionality and importance of the installation of X-Pack for Elasticsearch?

X-Pack is an extension that gets installed along with Elasticsearch. Various functionalities of X-Pack are security (Role-based access, Privileges/Permissions, Roles and User security), monitoring, reporting, alerting and many more.

How Migration API can be used as an Elasticsearch?

Migration API is applied after the Elasticsearch version is upgraded with a newer version. With migration API, X-Pack indices get updated into a newer version of the Elasticsearch cluster.

What is the difference between Master node and Master eligible no4de?

Master node functionality includes the creation of index/indices, monitor an account of nodes forming a cluster, deletion of index/indices. Whereas, Master eligible nodes are those nodes that get elected to become Master Node.

What is the difference between Term-based queries and Full-text queries?

Full-text queries analyze the query string before executing it whereas term-level queries operate on the exact terms stored in the inverted index without analyzing.

The full-text queries are commonly used to run queries on full-text fields like the body of an email whereas term level queries are used for structured data like numbers, dates, and enums, rather than full-text fields.

What are the various types of queries that Elasticsearch supports?

Queries are categorized into two types: Full Text/Match Queries and Term-based Queries.

Text Queries include basic match, match phrase, common terms, query-string, multi-match, match phrase prefix, simple query string.

Term Queries include term exists, type, wildcard, regexp term set, range, prefix, ids, and fuzzy.

How does a character filter in Elasticsearch Analyzer utilized?

Character filter in Elasticsearch analyzer is not mandatory. These filters manipulate the input stream of the string by replacing the token of text with corresponding value mapped to the key.

We can use mapping character filters that use parameters as mappings and mappings_path. The mappings are the files that contain an array of key and corresponding values listed, whereas mappings_path is the path that is registered in the config directory that shows the mappings file present.

Differentiate between Master node and Master eligible node in Elasticsearch?

Master node functionality revolves around actions across the cluster such as the creation of index/indices, deletion of index/indices, monitor or keeps an account of those nodes that form a cluster. These nodes also decide shards allocation to specific nodes resulting in stable Elasticsearch cluster health.

Whereas, Master – eligible nodes are those nodes that get elected to become Master Node.

What do you understand by multi-document APIs?

Multi-document API is a document API, which further has few more APIs. Multi-document APIs are basically used to perform queries across multiple documents. Simply says that - it allows the users to perform the operation in bulk like fetch or update multiple documents using a single query.

It is further classified and has the following APIs for bulk operations -

* Bulk API
* Multi Get API
* Delete By Query API
* Update By Query API
* Reindex API

What is the query language of Elasticsearch?

Apache Lucene query language which is also called as Query DSL is used by Elasticsearch.

What are common area of use Elasticsearch?

It’s useful in application where need to do analysis, statics and need to find out anomalies on data based on pattern.

It’s useful where need to send alerts when particular condition matched like stock market, exception from logs etc.

It’s useful with application where log analysis and issue solution provide because of full search in billions of records in milliseconds.

It’s compatible with application like Filebeat, Logstash and Kibana for storage of high volume data for analysis and visualize in form of chart and dashboards.

What are the basic operations you can perform on a document?

The following operations can be performed on documents

INDEXING A DOCUMENT USING ELASTICSEARCH.
FETCHING DOCUMENTS USING ELASTICSEARCH.
UPDATING DOCUMENTS USING ELASTICSEARCH.
DELETING DOCUMENTS USING ELASTICSEARCH.

What is Grok?

Grok is a filter plugin for Logstash that is used to parse unstructured data. It is often used for transforming Apache, Syslog and other webserver logs into a structured and queryable format for easier data analysis to be performed.

How can you make balanced shards?

Your clusters and/or shards are considered balanced when they have an equal number of shards across each node, thankfully Elasticsearch will run an automatic process of rebalancing shards which moves shards between the nodes that make up your cluster in order to improve its performance. You may need to take manual action if your configurations for forced awareness or allocation filtering clashes with Elasticsearch's attempts to automatically rebalance shards.

What is reindexing?

Reindexing your Elasticsearch index is mainly required in the event that you wish to update mapping or settings associated with your current index. Reindexing means that you are copying preexisting data from an index that already exists to a new destination index. The command endpoint _reindex can be used for this purpose.

What is WinLogBeat?

Winlogbeat is a log shipper used for collecting Windows event logs as it can easily read events from any event log channel using the Windows operating system. Windows log data once centralised within the ELK stack can then be monitored for anomaly detection & other security-related incidents.

What is Journalbeat?

Journalbeat is one of the most recent additions to the Beats family. This particular Beat is used to collect log entries from Systemd Journals. As with the other Beats, Journalbeat is based on the libbeat framework. Journalbeat is rated as being easier to use than more commonly known Beats for collecting Systemd Journal logs (such as Filebeat) but is regarded as an experimental Beat so may be subject to change.

What is Metricbeat?

Metricbeat is a metrics shipper built on the Libbeat framework. It originated from Topbeat (which has now been deprecated) and is primarily used for collecting metrics prior to their enrichment within Logstash for further processing within Elasticsearch & Kibana. Some users of Metricbeat may not wish to automatically push their metrics data to Logstash, in this instance they would likely use a service (for example Kafka or Redis) to buffer the data.

What is Filebeat?

Filebeat is the leading choice for forwarding logs to the Elastic Stack due to its reliability & minimal memory footprint. Filebeat was originally written in the Go programming language and its features originated from a combination of the best attributes of Logstash-Forwarder & Lumberjack. Additionally, when Filebeat is part of the logging pipeline it can generate and parse common logs to be indexed within Elasticsearch. You may often see Filebeat mentioned alongside Logstash as the two are used in tandem with each other for the majority of logging use cases.

What are common reasons that Kibana might be slow to load?

If you find that your Kibana instance is loading slowly it is often mentioned in the support forums that the reason this happens is due to the Apps bundle or apps themselves loading in the background.

Where are Kibana dashboards stored?

Kibana dashboards are stored in Elasticsearch under the default index kibana-int which can be edited within the config.js file if you wish to store your dashboards in a different location.

How can you create a Kibana dashboard?

Once you have Kibana loaded you will want to open the main menu and select Dashboard, from here you can select Create Dashboard. Once this step has been completed you will need to add panels of data to your dashboard for further visualisations and chart type selection to be applied.

How do you start Kibana?

When Kibana has been installed using a .tar.gz package on Linux, it can be started from the command line using the following command: ./bin/kibana For additional installation types & operating systems consult the following guide.

What is a Logstash pipeline?

A Logstash pipeline consists of these elements as listed in the following order: Input (the source of data), filter (processing, parsing & enrichment of data) & output (write the data for use within Elasticsearch & Kibana).

What is the step-by-step procedure to start an Elasticsearch server?

Follow the given steps to start an elasticsearch server

* First of all open, the command prompt from the windows start menu
* Change the directory to the bin folder of the elasticsearch folder which was created after its installation
* Type/Elasticsearch.bat and press enter to start the Elasticsearch server

By following these steps, Elasticsearch will start in CMD in the background. Further, open the browser and type http://localhost:9200, and press enter. This will show you the elasticsearch cluster name and meta value related to the database.

How can you forward logs from Kubernetes to Logstash?

By using a log shipper such as Filebeat, as illustrated on our integration page for sending Kubernetes logs to Logstash.

How can you use Logstash GeoIP?

The Logstash GeoIP filter is used to add supplementary information on the geographic location of IP addresses based on data available within the MaxMind GeoLite2 database.

What do you mean by fuzzy query Elasticsearch?

The fuzzy query returns the document that contains terms similar to the search terms. To find similar terms, a fuzzy query creates a set of possible variations of search terms within a specified edit distance. When a user searches for some terms using a fuzzy query, the system returns the most resembling terms for each expansion.

How to delete an index in Elasticsearch?

To delete an index in Elasticsearch, you have to create a query having DELETE as the request method and index name you want to delete.

DELETE index name

What is Query DSL in Elasticsearch?

Elasticsearch offers full Query DSL (Domain Specific Language) based on JSON to define queries.

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