A Technical I.T./DevOps Blog
Problem scenario
You use nmap and get this error from one server but not another:
Note: Host seems down. If it is really up, but blocking our ping probes, try -Pn
Nmap done: 1 IP address (0 hosts up) scanned in 3.05 seconds
There seems to be no intermediate firewall rule stopping one server. What should you do?
Solution
The error message suggests using “-Pn”.
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Problem scenario
You configured Nginx on a Linux server. You want to see if there has been activity on the website (e.g., via a web browser). What log file, visible on the back-end, has records of web browsing activity?
Solution
It is often here: /var/log/nginx/access.log
For general Nginx purposes, the nginx.conf file specifies the location of the Nginx logs and the names of the log files themselves.
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Question
What is a Continuous Application?
Answer
Databricks website says this “[w]e define a continuous application as an end-to-end application that reacts to data in real-time.”
The proper term should probably be “continual application” as there may be discrete moments where no data is coming in. Many streams can be interrupted. In fact, Structured Streaming, an aspect of Spark that is used in Databricks’ “continuous applications” is based on microbatching (according to this site).
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Problem scenario
You have an Amazon Aurora database in you AWS account. You want to see the status of this database with the AWS CLI. How do you list information about your Aurora databases?
Solution
Prerequisites
You must have the AWS CLI installed and configured with a user that has the ability to view Aurora databases (e.g., an administrator of your AWS account).
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Continue reading “How Do You Use the AWS CLI to List Aurora Databases?”
Problem scenario
You want to install Composer (a dependency manager for PHP) on your Debian/Ubuntu Linux server. What do you do?
Solution
sudo apt -y update
sudo apt -y install php-cli unzip
cd ~
sudo curl -sS https://getcomposer.org/installer -o composer-setup.php
HASH=curl -sS https://composer.github.io/installer.sig
echo $HASH
php -r “if (hash_file(‘SHA384’,
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Continue reading “How Do You Install Composer on Debian/Ubuntu Linux?”
Problem scenario
You have a heterogeneous enterprise network of servers. You want your Linux machines to communicate and transfer files with your Windows machines. You do not want to use Active Directory. What do you do?
Solution
1. Install Cygwin on the Windows server if it has not been set up already. If you need assistance with this, see this posting.
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Continue reading “How Do You Set up SSH on a Windows 2016 Server with Cygwin?”
Problem scenario
You have a Kubernetes cluster in AWS. You have the AWS CLI installed. How do you find the URL for the Kubernetes cluster?
Solution
1. Run this command: aws eks list-clusters
2. Run this command: aws eks describe-cluster foobar # where “foobar” was name determined in above command
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Problem scenario
You want to determine what VPC a given AWS server is in. How do you find this out?
Solution
Prerequisite
You must have the AWS CLI installed and configured with a user that has the ability to view EC-2 databases (e.g., an administrator of your AWS account). If you need assistance, see this posting.
Procedure
Run this command: aws rds describe-db-instances | grep -i vpc
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Continue reading “How Do You Find what VPC an EC-2 Instance Is In?”
Problem scenario
You want to make and test Ansible roles, and therefore you want to use Molecule. You are using RHEL version 8.x. You want to use Python 3 and Molecule. What should you do?
Solution
Prerequisites
i. You should install Docker. If you need assistance, see this posting.
ii. You should install these packages before hand:
sudo yum -y install gcc python3-devel
sudo dnf install -y redhat-rpm-config
Procedures
1.
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Continue reading “How Do You Install Molecule on RHEL v. 8.x with Python 3?”
Problem scenario
You want to know if a MapReduce job succeeded. What do you do?
Solution
Run one or both of these pairs of commands:
hadoop job -list all
hadoop job -list all | grep SUCCEEDED
mapred job -list all
mapred job -list all | grep SUCCEEDED
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Continue reading “How Do You Know if a MapReduce Job Succeeded?”