Add blog post about NoSQL datastores

docs/blog/index.rst

@@ -14,3 +14,4 @@ Blog
    command-line-engines
    search-indexer-engines
    sql-engines
+   search-database-engines

docs/blog/search-database-engines.rst

@@ -0,0 +1,95 @@
+===============================
+Query more of your NoSQL stores
+===============================
+
+From now on, searx lets you to query your NoSQL data stores:
+
+* `Redis`_
+* `MongoDB`_
+
+The reference configuration of the engines are included ``settings.yml`` just commented out,
+as you have to set various options and install dependencies before using them.
+
+By default, the engines use ``key-value`` template for displaying results.
+If you are not satisfied with the original result layout,
+you can use your owm template by placing the template under
+``searx/templates/{theme_name}/result_templates/{template_name}`` and setting
+``result_template`` attribute to ``{template_name}``.
+
+Futhermore, if you do not want to expose these engines on a public instance, you can
+still add them and limit the access by setting ``tokens`` as described in the `blog post about
+private engines`_.
+
+Configuring searx to use the stores
+===================================
+
+NoSQL data stores are used for storing arbitrary data without first defining their
+structure.
+
+Redis
+-----
+
+Reqired package: ``redis``
+
+Redis is a key value based data store usually stored in memory. 
+
+Select a database to search in and set its index in the option ``db``. You can
+either look for exact matches or use partial keywords to find what you are looking for
+by configuring ``exact_match_only``.
+
+In this example you can search for exact matches in your first database:
+
+.. code:: yaml
+
+  - name : mystore
+    engine : redis_server
+    exact_match_only : True
+    host : 127.0.0.1
+    port : 6379
+    password : secret-password
+    db : 0
+    shortcut : rds
+    enable_http : True
+
+
+MongoDB
+-------
+
+Required package: ``pymongo``
+
+MongoDB is a document based database program that handles JSON like data. 
+
+In order to query MongoDB, you have to select a ``database`` and a ``collection``. Furthermore,
+you have to select a ``key`` that is going to be searched. MongoDB also supports the option ``exact_match_only``, so configure it
+as you wish.
+
+Above is an example configuration for using a MongoDB collection:
+
+.. code:: yaml
+
+  - name : mymongo
+    engine : mongodb
+    shortcut : md
+    host : '127.0.0.1'
+    port : 27017
+    database : personal
+    collection : income
+    key : month
+    enable_http: True
+
+
+Acknowledgement
+===============
+
+This development was sponsored by `Search and Discovery Fund`_ of `NLnet Foundation`_ .
+
+.. _Redis: https://redis.io/
+.. _MongoDB: https://mongodb.com/
+.. _blog post about private engines: private-engines.html#private-engines
+.. _Search and Discovery Fund: https://nlnet.nl/discovery
+.. _NLnet Foundation: https://nlnet.nl/
+
+
+| Happy hacking.
+| kvch // 2021.07.13 23:16
+