How Do You Determine the IP Address Assignments of Running Docker Containers?

0 Comments

Problem scenario
You created some Docker containers and assigned them IP addresses. How do you find out what their IP addresses are?

Solution

1. Run this command: docker ps -a # find the container ID of the container you want to know about
2. Run this command but substitute “container_id” with the container ID you found above:
docker inspect -f ‘{{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}’ container_id

…

Continue reading “How Do You Determine the IP Address Assignments of Running Docker Containers?”

In Python, What Are Some Disadvantages with Calling a Function as a New Thread?

0 Comments

Question
Python supports the creation of new threads for [bound or unbound] functions. They can help with multiprocessing. If you want a server to begin certain operations in parallel with others, you may want to use new processes as opposed to new threads. Both threads and processes can provide the same parallel processing benefit. What are some disadvantages of using a thread to call a function?

…

Continue reading “In Python, What Are Some Disadvantages with Calling a Function as a New Thread?”

How Do You Set up a Send-Only (Postfix) Email Server on a Linux RHEL AWS Instance?

0 Comments

Problem scenario
You have a monitoring tool on a RedHat Enterprise Linux server that needs to send out emails upon certain events happening. You want to install and configure an email server. You need to send outbound emails, but you do not need to receive inbound emails. How do you configure RHEL to be able to send out regular emails over the internet?

Prerequisite
This assumes that Postfix has been installed.

…

Continue reading “How Do You Set up a Send-Only (Postfix) Email Server on a Linux RHEL AWS Instance?”

What Are The Kubernetes Concepts “pod label,” “label selector,” and “pod selector”?

0 Comments

Question
What is the difference between these three two-word terms “pod label,” “label selector,” and “pod selector”?

Answer
This answer provides details on what these are and provides some information on how they are different.

pod label: It is an inherent attribute of the pod. It can be changed via a command like this: kubectl label pod new-podlabel version=5.5 These statements were based on Assistanz.com.

…

Continue reading “What Are The Kubernetes Concepts “pod label,” “label selector,” and “pod selector”?”

How Do You Get the mysql Command to Work from an Ubuntu Linux Command Line?

0 Comments

Problem scenario
The mysql command does not work from Ubuntu. You try to run a “mysql” command but you get “command not found.” What do you do to install a mysql CLI utility?

Solution
Run one of the following:

sudo apt -y install mysql-client-core-5.7
sudo apt -y install mariadb-client-core-10.1

These commands may help you too:

apt-cache search mysql-client
apt-cache search mariadb-client
sudo apt -y install mycli
sudo mysql -u root

…

Continue reading “How Do You Get the mysql Command to Work from an Ubuntu Linux Command Line?”

What Do You Do when Cassandra Stalls on “Initializing IndexInfo”?

0 Comments

Problem scenario
When you start Cassandra you see a message such as this:

INFO [main] 2018-02-03 08:45:55,257 ColumnFamilyStore.java:389 – Initializing system.IndexInfo

What should you do?

Possible Solution #1
Try rebooting the server. This could help the problem.

Possible Solution #2
This next one is merely a workaround. It is not a best practice.

…

Continue reading “What Do You Do when Cassandra Stalls on “Initializing IndexInfo”?”

How Do You Troubleshoot Error Messages in a Bash Script?

0 Comments

Problem scenario
You run a shell or bash script but you receive an error message such as one of the following:

$’\r’: command not found
line:55 syntax error: unexpected end of file

Solution
Did you download the file from the internet directly to the Unix system? The root cause could be that there are invisible characters in the file.

…

Continue reading “How Do You Troubleshoot Error Messages in a Bash Script?”