How Do You Troubleshoot the Cassandra Problem about “Connection refused”?

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Problem Scenario
You have installed Apache Cassandra on Linux.  It is deployed as a single node configuration (not a cluster).  When you run “cqlsh” you get this error:

“Connection error: (‘Unable to connect to any servers’, {‘127.0.0.1’: error(111, “Tried connecting to [(‘127.0.0.1’, 9042)]. Last error: Connection refused”)})”

How do you troubleshoot cqlsh when you get this message “”Tried connecting to [(‘127.0.0.1’, 9042)].

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How Do You Install Zookeeper on Any Type of Linux?

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Updated on 5/14/20 with a minor update on 11/13/21

Problem scenario
You want to install Apache Zookeeper with a script.  You want the same script to work regardless of what distribution of Linux you are using (e.g., Ubuntu/Debian, RedHat (including CentOS/Fedora), or SUSE).  How do you write a script to install the latest version of Zookeeper?

Solution
The file that is attached called zki.txt is not needed but is attached as a reference copy of the below. 

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How Do You Install Apache Cassandra on Ubuntu 16.04?

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Problem scenario
You are running Ubuntu 16.x Linux and want to install Apache Cassandra.  How do you install Apache Cassandra on Linux Ubuntu Linux as a single-server configuration?

Solution
These directions will work to deploy Debian 9 Linux too.  They have been tested to work in AWS and GCP.

Prerequisites
i.  This solution assumes that you have installed Apache Ant and Git. 

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How Do You Install Apache Cassandra on a RedHat Derivative of Linux?

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Problem scenario
You want to install Apache Cassandra on CentOS, RHEL, or Fedora Linux.  What do you do?

Solution
These directions will deploy Apache Cassandra in a solo-server configuration.  This will not create a cluster.  These directions will work for a physical server, a VM, an EC-2 instance in AWS or a virtual machine in GCP.

Prerequisites
i.  This assumes that you have 3 GB of memory (in combination of either RAM or virtual memory,

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A List of Elastic Stack (Elasticsearch, Logstash, Beat, and Kibana) Books

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The Elastic Stack used to be called the ELK Stack; this link provides more information. 

Applied Network Security Monitoring: Collection, Detection, and Analysis by Chris Sanders and Jason Smith
The Art of Monitoring by James Turnbull
ElasticSearch 5.0 Cookbook – Third Edition by Alberto Paro
Elasticsearch Blueprints by Vineeth Mohan
Elasticsearch: A Complete Guide by Bharvi Dixit,

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What Are the Different Acronym Stacks in I.T.?

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Question
What are the different acronym stacks in I.T.?

Answer
There are many open source combinations of technologies that are in wide use.  These acronyms referred to as “full stacks” or “stacks” appear in articles and job descriptions.  A full stack is a bundle of software that (includes an OS and) can create a complete and functional product when properly configured. 

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How Do You Troubleshoot Mongodb when It Will Not Start and You Get This Error “Failed to start mongodb.service: Unit mongodb.service not found.”?

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Problem scenario
Using Linux you try to start the Mongodb service, but the service fails to start.  You get this error: “Failed to start mongodb.service: Unit mongodb.service not found.”  How do you fix this problem?

Solution
Verify you have this file: /etc/systemd/system/mongodb.service
Verify it has this content (with the last line being the “WantedBy=multi-user.target” stanza):

[Unit]
Description=High-performance, schema-free document-oriented database
After=network.target
Documentation=https://docs.mongodb.org/manual

[Service]
User=mongodb
Group=mongodb
ExecStart=/usr/bin/mongod –quiet –config /etc/mongod.conf

[Install]
WantedBy=multi-user.target

With Ubuntu 16 the command “systemctl start mongodb” (as root with no quotes) should start the Mongodb service.

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