Merge branch 'kamranahmedse:master' into master

content/roadmaps/101-backend/content/114-design-and-development-principles/103-solid.md

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-# Solid
+# SOLID
+
+SOLID is a set of principles applied to object-oriented design (OOD) to create maintainable, understandable, and flexible code, while avoiding code smells and defects. The principles are:
+
+- Single Responsibility
+- Open/Closed
+- Liskov Substitution
+- Interface Segregation
+- Dependency Inversion
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Original Paper' href='https://web.archive.org/web/20150906155800/http://www.objectmentor.com/resources/articles/Principles_and_Patterns.pdf'>Design Principles and
+Design Patterns</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.baeldung.com/solid-principles'>SOLID Principles</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://www.digitalocean.com/community/conceptual_articles/s-o-l-i-d-the-first-five-principles-of-object-oriented-design'>SOLID: The First 5 Principles of Object Oriented Design</BadgeLink>

content/roadmaps/101-backend/content/116-search-engines/100-elasticsearch.md

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-# Elasticsearch
+# Elasticsearch
+
+Elastic search at its core is a document-oriented search engine. It is a document based database that lets you INSERT, DELETE , RETRIEVE and even perform analytics on the saved records. But, Elastic Search is unlike any other general purpose database you have worked with, in the past. It's essentially a search engine and offers an arsenal of features you can use to retrieve the data stored in it, as per your search criteria. And that too, at lightning speeds.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+
+<BadgeLink colorScheme='blue' badgeText='Official Website' href='https://www.elastic.co/elasticsearch/'>Elasticsearch Website</BadgeLink>
+<BadgeLink colorScheme='blue' badgeText='Official Docs' href='https://www.elastic.co/guide/index.html'>Elasticsearch Documentation</BadgeLink>
+
+